Selina Concise Solutions for ICSE Class 8 Physics Chapter 8 Electricity

ELECTRICITY: “Is the rate of flow of electrons”. i = q/t
Electricity acts like water flowing through a pipe, where electrons are the tiny particles moving along the wire. This flow of charge allows us to power everything from small toys to large household appliances.
Teacher's Tip: Think of current (i) as the "speed" of the electricity river.
Exam Tip: Always write the formula i = q/t and define each symbol (q = charge, t = time) to score full marks.

To keep electrons move, potential difference is needed. This is done by a cell or battery.
Potential difference is the "push" that gets the electricity moving through the circuit. Without a battery or cell to provide this pressure, the electrons would simply stay still.
Teacher's Tip: A battery is like a "pump" for electrons.
Exam Tip: Remember that potential difference is always measured in Volts (V).

Potential difference: “is the amount of work done in moving a unit positive charge from one point to other.”
Potential difference V = {Work done } (W) / {charge moved } (Q)
Or W = QV but {charge} = it
Hence, W = VIt or {Electrical energy} = VIt
This describes the energy needed to move electricity from one spot to another in a wire. We calculate it by looking at how much work is being done on each little bit of electric charge.
Teacher's Tip: Use the "W-Q-V" triangle to remember the formula: W on top, Q and V on the bottom.
Exam Tip: When calculating energy (W), ensure your time (t) is converted into seconds for the standard formula.

Power: is “Rate of doing work”
P = W/t = VIt/t = VI
Power is measured in watt or J S^-1
1 { Watt} = 1 { Volt} × 1 { Ampere}
Power tells us how quickly an appliance uses up energy to do its job. A high-wattage bulb uses energy faster and shines brighter than a low-wattage bulb.
Teacher's Tip: Power is just "Energy per Second".
Exam Tip: Use the unit "Watt" (W) for power and "Joule" (J) for energy; don't mix them up.

S.I. unit of charge is coulomb (C).
S.I. unit of current is Ampere (A).
S.I. unit of P.D. is volt.
S.I. unit of electrical energy is Joule (J) and of power is watt (W)
1 { kWh} - 3600000 {J} = 3.6 × 10⁶ { J}
These units help scientists and engineers measure electricity exactly the same way all over the world. The Kilowatt-hour (kWh) is specifically used to measure the large amount of energy we use in our homes.
Teacher's Tip: "C-A-V-J-W" - learn these units like a secret code for electricity!
Exam Tip: For conversion questions, remember that 1 { kWh} is exactly 3.6 million Joules.

ELECTRIC power is generated at the GENERATING STATION at 11000 { volt}, or 11 { kV} as these stations are at very far off place from areas where it is to be used. The voltage (A.C.) is of 50 { HZ} frequency.
Electricity starts its journey at a very high voltage to make sure it can travel long distances without getting weak. The 50 { Hz} frequency means the current changes direction 50 times every single second.
Teacher's Tip: kV stands for Kilovolts (1000 { Volts}).
Exam Tip: Note the generation voltage (11 { kV}) as it is a common objective question.

AT GRID SUB-STATION this alternating current (A.C) voltage is stepped up from 11 { kV} to 132 { kV} to minise the loss of energy in transmission line wires.
Stepping up the voltage is like putting more pressure in a pipe so the water can reach a distant city faster. This high voltage helps prevent the electricity from turning into wasted heat during the long trip.
Teacher's Tip: "Step Up" means making the voltage higher for the long journey.
Exam Tip: Mention "minimizing energy loss" as the reason for stepping up voltage to get full marks.

At MAIN-SUB-STATION this voltage is stepped down from 132 { kV} to 33 { kV} and transmitted to city SUB-STATION.
As the electricity gets closer to your neighborhood, the voltage is lowered to make it safer to handle. This is the first of several "Step Down" stages in the power grid.
Teacher's Tip: Sub-stations act like "gateways" that control the flow of electricity.
Exam Tip: Remember the sequence: 11 { kV} → 132 { kV} → 33 { kV}.

At CITY SUB STATION, it is further stepped down from 33 { kV} to 220 { V} for supply to hourses for consumers.
The 220 { V} level is the standard "safe" voltage used for all the sockets and lights in our homes. This final step down makes the electricity ready for everyday use.
Teacher's Tip: 220 {V} is the magic number for home electricity in most places.
Exam Tip: Always specify that household supply is 220 { V}.

Colour coding: Live wire - Red or Brown
Neutral - Black or light blue
Earth wire - Green or yellow
Different colored plastic covers on wires help electricians know which wire carries the power and which one is for safety. Using the wrong wire can be very dangerous and cause accidents.
Teacher's Tip: "Red is for Danger" (Live), "Green is for the Earth" (Ground).
Exam Tip: Memorize both "Old" and "New" color codes as they are often compared in exams.

1 kWh = 1 unit: Power Rating on an appliance 100 { W} - 220 { V} means the appliance when worked on a 220 { V} will consume 100 { W} electricity power
This label tells you exactly how much energy a gadget will use when you plug it into a standard wall socket. If you use a 100 {W} bulb for 10 hours, it will use exactly 1 unit of electricity.
Teacher's Tip: Units are what the electric company uses to calculate your bill.
Exam Tip: Understand that "1 unit" specifically refers to 1 { kilowatt-hour}.

OVER LOADING: is the condition of Electric circuit, when it draws more current than it is designed for i. e. when a number of appliances are switched on at a time i.e. geyser, A.C. Electric motor etc. or a large number of plugs are put in the same socket.
Plugging too many things into one socket makes the wires carry more electricity than they can handle. This causes the wires to get very hot and can start an electrical fire.
Teacher's Tip: Don't let your sockets look like a "squid" with too many plugs!
Exam Tip: Define overloading as drawing "excess current" beyond the circuit's capacity.

EARTHING: is done in a house near the kWh meter. Earthing is a safety device which puts the appliance at zero potential.
Earthing provides a "safe path" for leaking electricity to go straight into the ground instead of through your body. It is a vital safety feature for any home wiring system.
Teacher's Tip: The Earth is like a giant sponge that soaks up extra electricity.
Exam Tip: Explain that earthing protects us from "electric shocks."

SHORT CIRCUITING: If the insulation on the wire of cable used f in the wiring (or used with an appliance) breaks. The LIVE WIRE COMES IN CONTACT WITH THE NEUTRAL WIRE, this result in SHORT CIRCUITING
When the two main wires touch directly without going through a bulb or fan, the electricity flows too fast and produces a huge spark. This usually happens when the plastic covering on old wires gets damaged or worn out.
Teacher's Tip: A short circuit is an "accidental shortcut" for electricity.
Exam Tip: State that a short circuit happens when the "Live wire touches the Neutral wire."

FUSE: “Is a device used to limit the current in an electric circuit”. The use of fuse protects the appliance in circuit from being damaged Fuse is always connected in live wire. A fuse wire should have
(i) High resistance
(ii) Low melting point.
These days miniature circuit breakers (MCB) are used. It is AUTOMATIC breaker, when current flowing excess.
A fuse is like a "safety guard" that melts and breaks the connection if the current gets too high. MCBs are more modern because they just "flip a switch" that you can reset later without replacing a wire.
Teacher's Tip: A fuse "gives its life" to save your expensive TV!
Exam Tip: Always list "Low Melting Point" and "High Resistance" as the two key properties of a fuse wire.

Appliances in a house are connected in parallel.
Parallel connection means that each light and fan has its own separate path to the power source. This way, if one bulb blows out, all the other lights in the house will keep working perfectly.
Teacher's Tip: Parallel means "Independent Paths".
Exam Tip: Mention that parallel circuits allow each appliance to receive the full 220 {V} voltage.

Test yourself

A. Objective Questions

1. Write true or false for each statement:

(a) A fuse wire has a high melting point.
Answer: False.
A fuse wire must have a low melting point so that it can melt quickly and break the circuit if the current becomes too high. If it had a high melting point, the dangerous current would keep flowing and could cause a fire.
Teacher's Tip: Think of a fuse as a "weak link" designed to break first for safety.
Exam Tip: When correcting this, always state that the melting point is *low*.

(b) Flow of protons constitutes electric current.
Answer: False.
Electric current is actually the flow of electrons, which are tiny negative particles. Protons stay locked inside the nucleus of the atom and do not move through the wire.
Teacher's Tip: Electrons "run", Protons "stay put".
Exam Tip: Define current specifically as the "rate of flow of electrons".

(c) Silver is an insulator of electricity.
Answer: False.
Silver is actually one of the best conductors of electricity in the world. However, it is too expensive to use for regular household wiring, so we use copper instead.
Teacher's Tip: Silver is the "Gold Medalist" of conductors.
Exam Tip: Distinguish clearly between conductors (allow flow) and insulators (block flow).

(d) S.I. unit and commercial unit of electrical energy are same.
Answer: False.
The S.I. unit of energy is the Joule (J), while the commercial unit we use for our bills is the Kilowatt-hour (kWh). One kWh is a much larger amount of energy than just one Joule.
Teacher's Tip: Joules are for "Science", kWh are for "Bills".
Exam Tip: Remember the conversion 1 { kWh} = 3.6 × 10⁶ { J}.

(e) Overloading of electric current in circuits can lead to short circuiting.
Answer: True.
When a circuit is overloaded, the wires get extremely hot, which can melt the plastic insulation around them. If the insulation melts away, the bare wires might touch each other and cause a short circuit.
Teacher's Tip: Heat from overloading is a wire's worst enemy.
Exam Tip: Identify the "melting of insulation" as the link between overloading and short circuits.

(f) Our body can pass electricity through it.
Answer: True.
The human body is a conductor because it contains a lot of water and salts. This is why it is extremely dangerous to touch live wires or electrical sockets.
Teacher's Tip: We are "Wet Conductors", so always be careful around electricity.
Exam Tip: Use the term "conductor" to describe the human body in electrical contexts.

(g) All metals are insulators of electricity.
Answer: False.
Almost all metals are excellent conductors of electricity because they have many free electrons. Insulators are usually non-metallic materials like rubber, plastic, or wood.
Teacher's Tip: Metals "carry", Insulators "stop".
Exam Tip: If asked to list conductors, metals like copper, iron, and silver are your best answers.

(h) The earth wire protects us from an electric shock.
Answer: True.
The earth wire provides a safe route for any stray electricity to travel into the ground. If a metal appliance becomes "live" due to a fault, the earth wire carries the current away so you don't get a shock.
Teacher's Tip: The Earth wire is like an "emergency exit" for electricity.
Exam Tip: Mention that the earth wire is connected to the "metal body" of the appliance.

(i) A switch should not be touched with wet hands.
Answer: True.
Water is a conductor, and wet skin has much less resistance than dry skin. If there is a tiny leak of electricity at the switch, wet hands could easily lead to a fatal electric shock.
Teacher's Tip: "Wet Hands + Electricity = Big Danger".
Exam Tip: Explain that water "increases conductivity" or "reduces resistance" for a more scientific answer.

(j) AH electrical appliances in a household circuit work at the same voltage.
Answer: True.
In a parallel circuit, every branch receives the same voltage from the mains. In our homes, this standard voltage is usually 220 { V}.
Teacher's Tip: Parallel circuits share the "Pressure" (V) equally.
Exam Tip: Specify that 220 { V} is the standard household voltage.

(k) In a cable, the green wire is the live wire.
Answer: False.
In modern color coding, the green (or green-yellow) wire is the Earth wire. The Live wire is usually Red or Brown.
Teacher's Tip: "Green is the Ground" is an easy way to remember.
Exam Tip: Know your color charts! Live = Red/Brown, Earth = Green/Yellow.

(l) A fuse is connected to the live wire.
Answer: True.
The fuse must be in the live wire so that if it melts, the entire appliance is disconnected from the power source. This makes the appliance safe to touch even if it has a fault.
Teacher's Tip: Putting a fuse in the "Live" wire cuts the power at the source.
Exam Tip: Always state that safety devices like fuses and switches are in the *Live* wire.

(m) A switch is connected to the neutral wire.
Answer: False.
A switch must always be connected to the live wire. If it were on the neutral wire, electricity would still reach the appliance even when the switch was turned off, which is dangerous.
Teacher's Tip: Switches go on the "Hot" (Live) wire to stay safe.
Exam Tip: Explain that a switch in the neutral wire doesn't "de-energize" the appliance.

2. Fill in the blanks

(a) The unit in which we pay the cost of electricity is kWh.
Answer: kWh.
The electric company counts how many "units" you use, where 1 unit equals 1 { kilowatt-hour} of energy. This is a practical way to measure large amounts of household energy use.
Teacher's Tip: kWh is the "unit of the bill".
Exam Tip: Don't confuse kW (power) with kWh (energy).

(b) The electrical energy consumed in a house is measured by kWh meter.
Answer: kWh meter.
This is the device (often called an electric meter) installed outside your house that records your energy consumption. It has dials or a digital screen that shows the total units used.
Teacher's Tip: The meter is like a "pedometer" for electricity.
Exam Tip: "Energy Meter" or "kWh Meter" are both acceptable terms.

(c) In a household electrical circuit, the appliance are connected in parallel with the mains.
Answer: parallel.
Parallel connections allow each appliance to work independently and receive the full supply voltage. This is much better than series, where if one light broke, all of them would go out.
Teacher's Tip: Parallel = "Each one on its own path".
Exam Tip: List "independent operation" and "constant voltage" as advantages of parallel circuits.

(d) A switch is connected to the live wire.
Answer: live.
Connecting the switch to the live wire ensures that when the circuit is "off", no electricity is flowing into the appliance at all. This prevents accidental shocks when changing a bulb or repairing a socket.
Teacher's Tip: Switches must control the "power wire" (Live).
Exam Tip: Mention "safety" as the reason for connecting switches to the live wire.

(e) The red colour insulated wire in a cable is the live wire.
Answer: live.
Red is the traditional color for the live wire in the old system (though brown is used in the new system). It acts as a warning because this wire carries the dangerous high voltage.
Teacher's Tip: Red = Stop/Danger = Live Wire.
Exam Tip: Be aware that modern wires might use brown instead of red for "Live".

(f) One kilowatt hour is equal to 3.6 × 10⁶ joule.
Answer: 3.6 × 10⁶.
This number comes from multiplying 1000 { watts} by 3600 { seconds} (which is one hour). It is the mathematical bridge between commercial units and scientific S.I. units.
Teacher's Tip: 1000 × 3600 = 3,600,000.
Exam Tip: Always use scientific notation (3.6 × 10⁶) in your answers for accuracy.

(g) A fuse wire should have low melting point.
Answer: melting point.
The metal in a fuse is chosen so it melts easily when it gets slightly too hot. This "breaking point" is what protects your whole house from dangerous electrical surges.
Teacher's Tip: A fuse is meant to "melt to save".
Exam Tip: The two properties are *Low Melting Point* and *High Resistance*.

3. Match the following
Column A                         Column B
(a) Electric power               (i) volt
(b) kWh                               (ii) joule
(c) Electric current              (iii) volt × ampere
(d) Electric energy              (iv) watt
(e) watt                                (v) ampere
(f) potential difference        (vi) electrical energy
Column A - Column B
(a) Electric power - (iv) watt
(b) kWh - (vi) electrical energy
(c) Electric current - (v) ampere
(d) Electric energy - (ii) joule
(e) watt - (iii) volt × ampere
(f) potential difference - (i) volt
Answer: (a)-(iv), (b)-(vi), (c)-(v), (d)-(ii), (e)-(iii), (f)-(i)
Matching physical quantities to their units is the first step in solving any physics problem. These relationships show how different parts of a circuit (like current and voltage) combine to create power and energy.
Teacher's Tip: Remember the formula P = VI to match Watt with Volt × Ampere.
Exam Tip: In matching questions, double-check that you haven't used the same unit for two different quantities.

4. Select the correct alternative

(a) All wires used in electric circuits should be covered with
1. colouring material
2. conducting material
3. an insulating material
4. none of the above
Answer: 3. an insulating material.
Insulation, like plastic or rubber, prevents electricity from leaking out or crossing into other wires. Without insulation, simply touching a wire would result in a dangerous shock.
Teacher's Tip: Insulation is like a "jacket" that keeps the electricity inside the wire.
Exam Tip: Rubber and plastic are the most common insulating materials.

(b) Electric work done per unit time is
1. electrical energy
2. electric current
3. electric voltage
4. electrical power
Answer: 4. electrical power.
Power is defined as the rate of doing work. In electricity, it describes how much energy is being transformed into light, heat, or movement every single second.
Teacher's Tip: "Rate" in physics almost always means "per unit time".
Exam Tip: The formula is P = W/t.

(c) One kilowatt is equal to
1. 100 { watt}
2. 1000 { watt}
3. 10 { watt}
4. none of these
Answer: 2. 1000 { watt}.
The prefix "kilo" always means one thousand. Just like 1 { kilometer} is 1000 { meters}, 1 { kilowatt} is exactly 1000 { watts}.
Teacher's Tip: "Kilo" = "Thousand".
Exam Tip: Always use 1000 as the multiplier for "kilo" conversions.

(d) Fuse wire is an alloy of
1. tin-lead
2. copper-lead
3. tin-copper
4. lead-silver
Answer: 1. tin-lead.
An alloy of tin (50%) and lead (50%) is used because it has the perfect combination of high resistance and a low melting point. Pure metals usually melt at too high a temperature to be good fuses.
Teacher's Tip: Tin and Lead are the "Power Couple" of fuse making.
Exam Tip: Specify that it is an "alloy" of tin and lead.

(e) A fuse wire should have
1. a low melting point
2. high melting point
3. very high melting point
4. none of the above
Answer: 1. a low melting point.
A low melting point (around 200°C) ensures the fuse wire breaks quickly if there's a problem. This speed is what saves your electronics from getting fried.
Teacher's Tip: Fuses are designed to be "weak" so they fail before your gadgets do.
Exam Tip: Do not mix up melting point (should be low) with resistance (should be high).

(f) When switch of an electric appliance is put off, it disconnects
1. the live wire
2. the neutral wire
3. the earth wire
4. the live and the neutral wire
Answer: 1. the live wire.
Turning off the switch breaks the path of the live wire, which is where the high voltage comes from. This makes the entire appliance safe because no energy can enter it.
Teacher's Tip: The switch is the "gatekeeper" of the Live wire.
Exam Tip: Mention that disconnecting the live wire is a key "safety requirement".

(g) The purpose of an electric meter in a house is
1. to give the cost of electricity directly
2. to give the consumption of electrical energy
3. to safeguard the circuit from short circuiting
4. to put on or off the mains.
Answer: 2. to give the consumption of electrical energy.
The meter tracks exactly how much electrical energy your family uses over time. The electric company then multiplies this consumption by a price rate to calculate your bill.
Teacher's Tip: The meter is like a "odometer" for energy.
Exam Tip: The unit shown on the meter is the kWh.

(h) If out of the two lighted bulbs in a room, one bulb suddenly fuses, then
1. other bulb will glow more
2. other bulb will glow less
3. other bulb will also fuse
4. other bulb will remain lighted unaffected.
Answer: 4. other bulb will remain lighted unaffected.
This is the major benefit of parallel circuits used in homes. Because each bulb has its own separate loop back to the power source, a failure in one branch doesn't affect the others.
Teacher's Tip: Parallel = Independence.
Exam Tip: Explain that in parallel circuits, every appliance has an "independent path".

B. Short/Long Answer Questions

Question 1: From where does the electricity come to our home ?
Answer: In our homes electricity comes from the CITY SUBSTATION.
Electricity is made at big power plants and then travels through heavy wires to substations in every city. These substations act as local distribution centers that send power through smaller lines to our street and into our homes.
Teacher's Tip: Think of electricity as a "delivery" that stops at the substation warehouse first.
Exam Tip: Name the "City Substation" as the direct source for your house wiring.

Question 2: What is an electric meter ? Where is it fixed in our house ?
Answer: ELECTRIC METER : Is ENERGY meter or kWh meter and measures the amount of electric energy consumed in kWh for which electricity bill is paid. It is connected through a cable after company fuse on the front or outside wall of the house.
This device is like a "silent bookkeeper" that records exactly how much energy flows into your house. It is placed on an outside wall so that meter readers can check the dials easily without entering your home.
Teacher's Tip: "Electric meter" is just another name for "Energy meter".
Exam Tip: State that it measures "Electrical Energy" in "kWh".

Question 3: State the purpose of kWh meter.
Answer: Purpose of kWh meter is to measure the electric energy consumed in kWh for which the electricity bill is to be paid. i.e. units of energy consumed.
The kWh meter provides an accurate record of your energy usage for both the consumer and the electricity company. Without it, there would be no fair way to calculate the cost of power used in a building.
Teacher's Tip: kWh meter = Energy Tracker.
Exam Tip: Always link the kWh meter to "calculating the electricity bill".

Question 4: For which unit do we pay our electricity bill ?
Answer: UNIT - is boad of trade unit i. e. 1 { kWh} = 1000 { W} used in 1 { hour}.
We pay per "unit" of energy, which is standard around the world. One unit is enough energy to run a 1000-watt heater for one full hour.
Teacher's Tip: "kWh" is the legal commercial unit of electricity.
Exam Tip: Use the full name "Kilowatt-hour" or the symbol "kWh".

Question 5: How can you check just by seeing the meter whether the electricity is in use or not ?
Answer: If the electricity is in use, the counter fixed on the armature of the meter rotates and reads the number of rotations (A red mark is seen rotating).
Old-style meters have a spinning metal disk inside that moves faster when more lights and fans are turned on. In modern digital meters, you will see a blinking light or numbers changing to show energy is being used.
Teacher's Tip: No spinning/blinking = No electricity being used.
Exam Tip: Mention the "rotating red mark" or "armature" to describe old meters.

Question 6: The diagram below in figure shows the reading on the dials of a meter. State what is its reading.
Answer: The reading 2789 is 2789.
Reading meter dials is like reading a clock; you look at where the pointer is on each circle. By combining the four numbers from left to right, you get the total units of energy recorded.
Teacher's Tip: Read the dials from left to right, like a sentence.
Exam Tip: If a pointer is between two numbers, always pick the smaller number.

Question 7: One day the meter reading is found to be 7643 units while next day, it was 7657 units. What is the consumption of electricity in a day ?
Answer: Final reading 7657 units; Initial reading 7643 units; Consumption of electricity in a day = Final reading - initial reading = 7657 - 7643 = 14 { units}.
To find out how much power you used, you just subtract the old number from the new one. This calculation tells you exactly how many "units" passed through the meter in that 24-hour period.
Teacher's Tip: Consumption = "New Reading - Old Reading".
Exam Tip: Always show your subtraction work to earn full marks.

Question 8: A source of potential difference V volt sends current I ampere in a circuit for time t second. Write expressions for (a) electrical energy supplied by the source, and (b) electrical power spent by the source.
Answer: Potential difference V is the work done in moving a unit charge.
therefore Work done in moving a charge Q through pot. diff. V = QV i.e. W = QV but Q / t = I Or Q = It therefore W = VIt. Work done = Electrical energy.
(a) therefore Electrical energy = VIt is the expression.
(b) Power is the rate of doing W. P = W/t = VIt/t = VI. P = VI is the expression.
These formulas are the heart of electricity physics. They link the "push" of the battery (V), the "flow" of electrons (I), and the "time" (t) to tell us exactly how much energy is being moved.
Teacher's Tip: Memorize "VIP" (V × I = P) - it's very important!
Exam Tip: Derive the power formula starting from W = QV to show your depth of understanding.

Question 9: Name the unit in which you pay the cost of your electricity bill. How is it related to joule ?
Answer: UNIT in which the electricity bill is charged is board of TRADE UNIT = kWh. 1 { Unit} = 1 { kWh} = 3600000 { J} = 3.6 × 10⁶ { J}. 1 { kWh} = 3.6 × 10⁶ { J}.
The kWh is the commercial "mega-unit" because the Joule is too small for home use (it's like measuring a marathon in millimeters!). One kWh is the same as 3.6 million Joules of energy.
Teacher's Tip: Bill units are called "kWh".
Exam Tip: Know the conversion: 1 { kWh} = 3.6 { Megajoules}.

Question 10: If an appliance of power P watt is used for time t hour. How much electrical energy is consumed in kWh.
Answer: Power P = {Electrical energy} / t.
therefore Electrical energy = P × t.
Energy is simply how much power you use and how long you use it for. By multiplying the wattage by the hours, you get the total energy consumption in watt-hours, which can be converted to kWh.
Teacher's Tip: Energy = Power × Time.
Exam Tip: If power is in watts, divide by 1000 to get kWh.

Question 11: What is an electric fuse ? State its purpose in the household electrical circuit.
Answer: FUSE: “Is a safety device which is used to limit the current in an electric circuit. PURPOSE OF FUSE IN HOUSE HOLD CIRCUIT : It safe guards the circuit and the appliances connected in the circuit from being damaged if the current in the circuit exceeds the specified value due to voltage fluctuation or short circuiting.
A fuse is like a "suicide guard" for your gadgets; it breaks itself to stop too much electricity from entering. This prevents wires from catching fire if there's a surge or if too many things are plugged in.
Teacher's Tip: The fuse is the most important "weak point" in a circuit.
Exam Tip: Mention "protecting appliances" and "preventing fire" as the two main purposes.

Question 12: State one property of the material of a fuse wire.
Answer: Two CHARACTERISTICS OF FUSE WIRE are: (i) Has LOW MELTING POINT. (ii) Has HIGH RESISTANCE.
A fuse wire needs to be "stubborn" (high resistance) so it gets hot easily, but also "soft" (low melting point) so it snaps quickly once it gets hot. These two features work together to break the circuit in less than a second if things get dangerous.
Teacher's Tip: "Hot and Meltable" - the fuse motto!
Exam Tip: List both properties even if asked for one to secure full marks.

Question 13: Name the material of a fuse wire.
Answer: MATERIAL used is an ALLOY of LEAD (50%) and TIN (50%) having low M.P. of 200°C.
While regular wires are made of copper to keep things cool, fuse wires are made of this special mix to ensure they melt exactly when they should. This alloy has a much lower melting point than most household metals.
Teacher's Tip: Lead + Tin = Safe Fuse.
Exam Tip: Remember the percentages (50/50) and the melting temperature (200°C).

Question 14: Can we use copper wire as a fuse wire ? Give reason.
Answer: Copper wire cannot be used as a fuse wire since meting point of Cu is higher and resistance is very low and current can flow through it without melting it and without breaking the circuit.
Copper is designed to stay solid and carry current easily, which is the exact opposite of what a fuse needs to do. If you used copper as a fuse, it wouldn't melt in time to stop a fire if too much power flowed through.
Teacher's Tip: Copper is "too strong" to be a fuse.
Exam Tip: Mention "high melting point" and "low resistance" of copper as the reasons it fails as a fuse.

Question 15: How does a fuse protect the electric wiring (or an appliance) from being damaged ?
Answer: Due to voltage fluctuations or insulation on the wire of cable gets worn and tom (breaks), the live wire comes in contact with neutral wire and results in SHORT CIRCUIT. To prevent this damage, a fuse is used in the LIVE WIRE. The fuse wire gets heated up to the extent that it melts, a gap is produced in the live wire and the circuit becomes incomplete, no current flows and the appliance is saved.
As soon as the electricity starts flowing too fast, the fuse gets so hot that it literally turns into a liquid and drips away. This creates a gap in the wire (like a broken bridge) that the electricity cannot cross, stopping the power before it can do any harm.
Teacher's Tip: A melted fuse = an incomplete circuit.
Exam Tip: Explain the step-by-step process: heating → melting → gap → circuit break.

Question 16: Which fuse wire is thick : 5 { A} or 15 { A} ?
Answer: therefore R propto l/a. More the area, lesser is the resistance and more is the current flowing. therefore 15 { A} fuse wire is thick.
The 15 { A} wire is used for big appliances like geysers and A.Cs, so it needs to be thicker to carry more electricity without melting too early. The 5 { A} wire is for small things like lights, so it is much thinner.
Teacher's Tip: More Amps = Thicker Wire.
Exam Tip: Relate thickness (area) to the current-carrying capacity.

Question 17: Write the full form of M.C.B.
Answer: Miniature Circuit Breaker.
MCBs are the modern "switches" you see in the gray box in your home's hallway. Unlike old fuses, they don't break; they just flip down to "Off" and can be flipped back "On" once the problem is fixed.
Teacher's Tip: MCB is like a "renewable fuse".
Exam Tip: Spelling counts - make sure to get "Miniature" correct.

Question 18: How is M.C.B. superior to the fuse wire ?
Answer: M.C.B. automatically fall down and switch off the circuit in very short time, when excessive flow of electric current in a circuit. It is raised up after the fault is rectified.
MCBs are faster at reacting to danger than old fuses, and you don't need to replace any wires when they "trip". They are much more convenient for homeowners because they work automatically and are easy to reset.
Teacher's Tip: Fuses are "one-time use", MCBs are "re-usable".
Exam Tip: Emphasize that MCBs are "automatic" and "fast-acting".

Question 19: With which wire: live or neutral is the fuse wire connected?
Answer: Fuse is connected with LIVE WIRE.
Connecting the fuse to the live wire is a safety rule. If the fuse was in the neutral wire and it melted, the appliance would still be connected to the "hot" power wire, which could still give you a dangerous shock.
Teacher's Tip: Live wire is where the "fire" is, so the fuse goes there.
Exam Tip: Fuses and switches always go in the *Live* wire.

Question 20: What do you mean by short circuiting of a circuit ?
Answer: SHORTCIRCUIT: If the insulation on the wire of cable used in the wiring (or used with an appliance) breaks, THE LIVE WIRE COMES IN CONTACT WITH THE NEUTRAL WIRE, This results in a SHORT CIRCUIT.
A short circuit happens when electricity finds an "easy path" to follow instead of going through the appliance. Because there is no resistance, a huge amount of electricity flows instantly, causing heat and sparks.
Teacher's Tip: Short circuit = Live touches Neutral.
Exam Tip: Mention "damaged insulation" as the main cause of short circuits.

Question 21: Figure shows two ways of connecting the three bulbs A, B and C to a battery. Name the two arrangements. Which of them do you prefer to use in a household circuit ? Give a reason to support your answer.
Answer: (a) is SERIES arrangement. (b) is parallel arrangement. A PARALLEL arrangement of bulbs is preferred as if one of the bulbs gets fused, the other two will keep glowing.
In series, all bulbs share one path, so if one fails, the whole line goes dark (like old Christmas lights). In parallel, each bulb has its own path, which is much more reliable for our homes.
Teacher's Tip: Parallel is like a "ladder" with many rungs.
Exam Tip: State that in parallel, each appliance gets "full mains voltage".

Question 22: How are the electrical appliances connected in a house circuit: in series or in parallel ? Give reason.
Answer: ELECTRICAL appliances in a house are connected in PARALLEL as :
(i) Each appliance gets full voltage as resistance in parallel becomes low.
(ii) If fuse of one appliance is fails it does not effect the working of other appliances.
(iii) We can light one bulb without lighting the other bulbs.
Parallel connection is the gold standard for home wiring because it offers independence. It means you can turn off the bathroom light without accidentally turning off your computer!
Teacher's Tip: Parallel = Independence & Full Voltage.
Exam Tip: List at least two reasons (full voltage and independent switching) for full marks.

Question 23: In the household electric circuit, if one bulb is fused in a room, the other bulbs keep glowing. Explain the reason.
Answer: In the house hold electric circuit the appliances are connected in parallel and each appliance has an independent path for current and work at the same voltage. Hence, if one bulb in a room is fused, the other bulbs keep glowing.
Since electricity has multiple paths to travel in a parallel circuit, a break in one path (the fused bulb) doesn't stop the flow in the other paths. The "river" simply flows through the remaining open channels.
Teacher's Tip: Each bulb has its "own private road" to the battery.
Exam Tip: Use the keyword "independent path" to explain the parallel circuit behavior.

Question 24: State the voltage at which electricity is supplied to our houses.
Answer: Electricity voltage is supplied to our houses at 220 { volt}.
This is the standard pressure of electricity coming from your wall sockets. While power plants make much higher voltages, this is what is safely stepped down for our gadgets and appliances to use.
Teacher's Tip: Just remember "Double-Two-Zero" (220).
Exam Tip: Always include the unit "Volt" or "V" in your answer.

Question 25: Draw a labelled diagram with the necessary switches to connect a bulb, a fan and a plug socket in a room with the mains. In what arrangement will you connect them to the mains ?
Answer: [Textbook provides a diagram showing the Mains connected to a Switch, Bulb, Socket Outlet, Regulator, and Fan in a parallel arrangement].
All three - the bulb, fan, and socket - must be in parallel so they can each have their own switch. This way, you can plug in your charger without having to keep the fan or the light turned on at the same time.
Teacher's Tip: Every device gets its "own switch" in a parallel home circuit.
Exam Tip: When drawing, make sure the switch is always on the "Live" wire side.

Question 26: State the colour coding of the three wires in a cable used for
Answer: COLOUR CODING OF THREE WIRES :
Live wire: Old - Red; New - Brown
Neutral wire: Old - Black; New - Light blue
Earth wire: Old - Green or yellow; New - Green or yellow
Colors are used like labels to prevent dangerous mistakes during repairs. Knowing both the old and new colors is important because older houses might still have red and black wires, while newer ones will have brown and blue.
Teacher's Tip: Live is Brown (like the ground, but it's the "hot" one!), Neutral is Blue.
Exam Tip: Draw a table to show the comparison between old and new color codes.

Question 27: Why is the metal covering of an electrical appliance earthed?
Answer: EARTHING OF THE APPLIANCE : To protect from the electric shock electric appliance is earthed. Sometimes due to break of insulation of wires, live wire comes in contact with the body of appliance and we get a fatal shock when the appliance is touched. If the appliance is earthed, the current will pass to the earth and we remain protected from the electric shock.
If a wire inside your washing machine touches the metal frame, the whole machine becomes dangerous to touch. The earth wire "traps" that electricity and sends it safely into the ground, often blowing the fuse to tell you there's a problem.
Teacher's Tip: Earthing "drains away" the danger.
Exam Tip: Mention that earthing is especially needed for appliances with "metal bodies".

C. Numericals

Question 1: An electrical appliance is rated as 60 { W} - 150 { V}.
(a) What do you understand by this statement ?
(b) How much current will flow through the appliance when in use ?
Answer: (a) 60 { W} - 150 { V} power rating of appliance means, “If appliance is put in circuit on 150 { volt}, it will consume 60 { w} electrical power i.e. electric energy consumed by it in 1 { sec. is } 60 { J}.
(b) P = VI therefore Current will through the appliance I =P/V = 60w/150 v = 0.4 { A}.
The rating tells you two things: what power source it needs and how much energy it will use. By dividing the wattage by the voltage, you can calculate exactly how much "flow" (current) the appliance needs.
Teacher's Tip: I = P/V is the formula to use here.
Exam Tip: Always include the units (W, V, A) in your final calculation steps.

Question 2: An electric iron of power 1.5 { kW} is used for 30 { minute} to press the clothes. Calculate the electrical energy consumed in (a) kilowatt hour (b) joule.
Answer: P = W/t therefore Electrical energy W = P × t. P = 1.5 { kW}; t = 30 { minute} = 1/2 { hr}. 1.5 × 1/2 = 0.75 { kWh}.
(b) 1 { kWh} = 3.6 × 10⁶ { J}.
therefore 0.75 { kWh} = 0.75 × 3.6 × 10⁶ = 2.700 × 10^6 = 2.7 × 10⁶ { J}.
To find energy in kWh, you must have your time in hours (30 { min} = 0.5 { hours}). Once you have the kWh, you multiply by 3.6 million to convert it into the standard scientific Joule unit.
Teacher's Tip: Don't forget to convert minutes to hours first!
Exam Tip: Show the multiplication steps for the conversion to Joules clearly.

Question 3: Assuming the electric consumption per day to be 12 { kWh} and the rate of electricity to be ₹ 6.25 per unit, find how much money is to be paid in a month of 30 { days} ?
Answer: Electric energy consumed per day = 12 { kWh} = 12 { units}. Electric energy consumed in 30 { days} = 12 × 30 = 360 { units}. Cost to be paid in 1 { month} = 360 × 6.25 = ₹ 2250.
First, find the total "units" used for the whole month by multiplying the daily use by 30. Then, just like buying apples, multiply the total units by the price per unit to get the final bill amount.
Teacher's Tip: One unit = 1 { kWh}.
Exam Tip: Always mention the currency (₹) in your final money answer.

Question 4: In a premise 5 { bulbs} each of 100 { W}, 2 { fans} each of 60 { W}, 2 { A.Cs} each of 1.5 { kW} are used for 5 { h} per day. Find : (a) total power consumed per day, (b) total power consumed in 30 { days}, (c) total electrical energy consumed in 30 { days}, (d) the cost of electricity at the rate of ₹ 6.25 per unit.
Answer: Power consumed by:
5 { bulbs} = 5 × 100 = 500 { W}
2 { fans} = 2 × 60 = 120 { W}
2 { A.C} = 2 × 1.5 × 1000 = 3000 { W}
(a) Total power consumed per day = 500 + 120 + 3000 = 3620 { W}.
(b) Total power consumed in 30 { days} =3620/1000 × 30 = 108.6 { kW}. (Note: This is total power rating over 30 days period).
(c) Electric energy is used for 5 { h} per day. Total electrical energy consumed in 30 { days} = 108.6 × 5 = 543 { kWh}.
(d) Cost of electricity = P × t = 543 × 6.25 = ₹ 3393.75.
This multi-step problem mimics a real house electricity bill. You sum up all the appliance wattages, multiply by the daily usage hours, then multiply by the days in a month and finally the electricity rate.
Teacher's Tip: Add all the "Watts" first, then convert the final sum to "kW" by dividing by 1000.
Exam Tip: Be careful with the A.C. power; 1.5 { kW} is 1500 { W}! Ensure all units are in Watts before adding.

Exercise 8 B

STATIC ELECTRICITY: “The substances like glass, plastic, ebonite, amber, nylon etc. when rubbed with wool, fur or silk produces electric charge or static charge called static electricity.”
Static electricity is charge that "stays put" on the surface of an object instead of flowing like current. You often notice this when you get a tiny spark from a doorknob or when your hair stands up after pulling off a sweater.
Teacher's Tip: "Static" means "standing still".
Exam Tip: Rubbing is the key method for creating static electricity.

Glass rod when rubbed with silk, glass is charge positively and silk is negatively charged.
Ebonite rubbed with fur, ebonite is charged negatively and fur is charged positively.
Plastic comb rubber with dryhair is -vely charged. Rubber balloon rubbed with woollen cloth is negatively charged.
These materials "trade" electrons during the rubbing process. Some materials are more "greedy" for electrons than others, which is why they get a specific type of charge (+ or -).
Teacher's Tip: Glass is (+), Silk is (-). Ebonite is (-), Fur is (+).
Exam Tip: Memorize these pairs as they are very common in multiple-choice questions.

Charged bodies (+ve or -ve) attract small pieces of paper, glass dust etc.
Like charged REPEL each other and unlike charges ATTRACT each other i.e. +ve and negative attract and +ve repels +ve.
Two rubber balloons rubbed with woollen cloth (each -vely charged) REPEL each other. A balloon charged -vely moves towards wall (uncharged body) i.e. a charged body attracts uncharged body.
The basic rule of electricity is that opposites like each other, while similar charges want to stay far apart. An uncharged body will always be attracted to a charged one because the charges inside it shift around.
Teacher's Tip: "Likes Repel, Opposites Attract".
Exam Tip: Always mention "force of attraction" or "force of repulsion" when discussing two charged bodies.

CONDUCTORS : “Substances which allow electricity to flow through them are conductors, e.g. silver, copper, iron, aluminium - all metals human body, impure water, wet cloth, wet wood.
Conductors are materials where electrons can easily "slide" from one atom to another. This is why all the wires in your house are made of metal and why you shouldn't touch them with your bare hands.
Teacher's Tip: Metals are the best "highways" for electricity.
Exam Tip: Use "Silver" as the example for the best conductor and "Copper" for the most commonly used one.

INSULATORS or BAD CONDUCTORS or poor conductors : “Substances which do not allow the electricity to flow through them.” e.g. Rubber, glass, mica, dry cloth or dry wood, polythene, wax, wool, pure water etc.
Insulators have electrons that are "glued" tightly to their atoms and refuse to move. This makes them perfect for safety covers on tools, plugs, and wire cables.
Teacher's Tip: Insulators are the "bouncers" that stop electricity from passing.
Exam Tip: Pure water is an insulator, but tap water (impure) is a conductor - don't get confused!

Conductors can be charged by (i) Conduction (b) Induction
These are two ways to give an object an electrical charge using a body that is already charged. One involves physical touching, while the other works just by bringing them close together.
Teacher's Tip: Conduction = Contact; Induction = Influencing from a distance.
Exam Tip: Be ready to explain the difference between these two methods in a short answer.

CONDUCTION: A charged body when touches (or in contact with) uncharged body. Charge of the same kind is produced on uncharged body i.e. charge is shared.
In conduction, the electricity literally "overflows" from the charged object into the empty one. It's like pouring water from one bucket into another until they both have the same level.
Teacher's Tip: Conduction starts with "C" for "Contact".
Exam Tip: State that conduction results in the *same* kind of charge on both bodies.

INDUCTION : When a charged body is brought near uncharged body the uncharged body is charged and charge remains on body so long as the charged body remains near the uncharged body. Nearer end gets oppositely charged called bound charge and farther end has similar charge called free charge.
Induction is like "scaring" the charges; a positive rod pulls all the electrons to one side of an object without even touching it. Once you take the rod away, the charges usually go back to normal unless you ground the object.
Teacher's Tip: Induction is like "magnetic-style" charging - no touching required.
Exam Tip: Mention "Bound Charge" and "Free Charge" to show advanced knowledge.

ELECTROSCOPE: is a device which is used to detect the presence and nature (kind) of charge on a body, (i) pith ball pendulum and (ii) Gold leaf electroscope (G.L.E.S.) are two devices.
These tools are like "charge detectors" that show us invisible electricity. They use lightweight parts like gold leaves or pith balls that move to show if an object is bringing electricity near them.
Teacher's Tip: Electroscopes make the "invisible" visible.
Exam Tip: "Gold Leaf Electroscope" is the most sensitive type.

During thunder storm when a charged cloud passes over earth or other cloud, due to induction opposite charge is induced and a spark may occur between two oppositely charge clouds (as two nacked electric wires are brought near each other. As they come closer, a spark is produced with crackling sounds). This spark is called LIGHTNING
Lightning is just a giant static spark, exactly like the small one you might feel on a rug, but on a massive scale. The clouds act as giant batteries that suddenly discharge their energy through the air.
Teacher's Tip: Lightning is "Space Static".
Exam Tip: Mention that lightning is caused by "Electric Discharge" between clouds or cloud and earth.

LIGHTNING CONDUCTOR: is a device to save the high buildings from LIGHTNING
This is a pointed metal rod on top of skyscrapers that "invites" the lightning to hit it instead of the building. It then safely carries that massive energy through a thick wire straight into the ground.
Teacher's Tip: It's like a "security guard" that catches lightning.
Exam Tip: State that a lightning conductor is always made of a good conductor like "Copper".

Test yourself

A. Short Answerwer Questions

1. Write true or false for each statement:

(a) The number of electrons and protons in an atom are same.
Answer: True.
In a normal, neutral atom, the positive protons in the center and the negative electrons around the outside perfectly balance each other out. This is why most things we touch don't give us a shock!
Teacher's Tip: Perfect Balance = Zero Net Charge.
Exam Tip: An atom with unequal numbers is called an "ion".

(b) If the charge is not in motion, we call it static electricity.
Answer: True.
Static electricity refers to the buildup of electric charge on the surface of an object. Unlike the electricity in our walls, it stays in one place until it has a chance to jump to another object.
Teacher's Tip: Static = Stationary.
Exam Tip: Contrast static electricity with "current electricity" which involves moving charges.

(c) Human body is a conductor of electricity.
Answer: True.
Our bodies are mostly made of water and minerals that conduct electricity very well. This is why we must always follow safety rules when using electrical gadgets.
Teacher's Tip: We are "walking conductors".
Exam Tip: State that "impure water in cells" makes the human body a conductor.

(d) When an ebonite rod is rubbed with fur, the electrons move from ebonite to fur.
Answer: False.
Correct: When an ebonite rod is rubbed with fur, the electrons move from fur to ebonite. Ebonite is "stickier" for electrons, so it pulls them away from the fur during rubbing.
Teacher's Tip: Ebonite is an "electron thief"!
Exam Tip: Remember that Ebonite always becomes *Negative* after rubbing with fur.

(e) When, glass rod is rubbed with dry silk cloth, the electrons move from glass to silk.
Answer: True.
Silk has a stronger pull on electrons than glass does. During rubbing, the silk steals electrons, making the glass positively charged and the silk negatively charged.
Teacher's Tip: Glass loses, so it's "Positive" (+).
Exam Tip: Glass rod + Silk = Positive rod.

(f) The cap of gold leaf electroscope is made of copper.
Answer: False.
Correct: The cap of gold leaf electroscope is of brass. Brass is a great conductor and is sturdy enough to hold the metal disc and rod together.
Teacher's Tip: Gold leaf inside, Brass cap on top.
Exam Tip: Name "Brass" specifically as the material for the cap.

(g) If a glass rod rubbed with silk is brought near the cap of a negatively charged electroscope, the divergence of leaves will decrease.
Answer: True.
The positive glass rod pulls some of the negative electrons away from the gold leaves up toward the cap. With fewer negative charges in the leaves, they repel each other less and the gap between them narrows.
Teacher's Tip: Opposites attract, so the rod "calls" the charges up.
Exam Tip: Use "attractive force" to explain why divergence decreases.

(h) In induction, a positively charged body can make an uncharged body positively charged.
Answer: False.
Correct: In induction, a positively charged body can make an uncharged body negatively charged. Induction always creates an *opposite* charge at the end closest to the charging body.
Teacher's Tip: Induction = Opposite Charge at the near end.
Exam Tip: Induction *always* produces opposite charge at the closer side.

(i) A lightning conductor saves the building from lighting.
Answer: True.
By providing a direct, low-resistance path to the ground, the conductor ensures the massive energy of a lightning strike bypasses the fragile parts of the building.
Teacher's Tip: It "conducts" the danger away.
Exam Tip: Mention "Earthing" as the process used by a lightning conductor.

(j) When a comb is rubbed with dry hair both comb and paper get similarly charged.
Answer: False.
Correct: A comb rubbed with hair and brought near pieces of paper attracts them, because both have dissimilar charges. The comb gets a negative charge and induces a positive charge on the paper.
Teacher's Tip: If they were similar, the paper would fly *away* from the comb!
Exam Tip: Attraction means the charges *must* be opposite or one is neutral.

(k) A glass rod rubbed with silk repels an ebonite rod rubbed with fur.
Answer: False.
Correct: A glass rod rubbed with silk attract an ebonite rod rubbed with fur. Since the glass is positive and the ebonite is negative, they are drawn toward each other.
Teacher's Tip: Glass is (+), Ebonite is (-). They are a perfect match!
Exam Tip: Always check the signs (+ or -) before deciding between attraction and repulsion.

(l) When a ebonite rod is rubbed with fur, the protons move from the ebonite rod to the fur.
Answer: False.
Correct: When a ebonite rod is rubbed with fur, the free electrons move from the fur to the ebonite rod. Protons are heavy and stuck in the nucleus; they never move during rubbing.
Teacher's Tip: Only Electrons move, Protons stay home.
Exam Tip: Use "transfer of electrons" to explain all types of static charging.

(m) A conductor has a large number of free electrons.
Answer: True.
Free electrons are like "loose change" that can be easily moved from one atom to another. This is exactly what allows electricity to flow through metals so easily.
Teacher's Tip: Free electrons = Ability to flow.
Exam Tip: Name "free electrons" as the reason metals conduct electricity.

(n) An ebonite rod can be charged by touching it with a charged copper rod.
Answer: False.
Correct: An ebonite rod can be charged by not touching it with a charged copper rod, will be charged by induction method. Ebonite is an insulator, so conduction (touching) doesn't work well for charging it.
Teacher's Tip: Insulators are hard to charge by just touching.
Exam Tip: Use "Induction" or "Rubbing" for charging insulators like ebonite.

(o) To find whether a body is charged or not, an uncharged electroscope is used.
Answer: True.
Bringing a charged object near an uncharged electroscope will make its parts (pith ball or gold leaves) move. If they don't move at all, the body you are testing is uncharged.
Teacher's Tip: Movement = Charge present.
Exam Tip: Detection of charge is the main use of a simple electroscope.

(p) To find whether the charge on a body is positive or negative, an uncharged electroscope is used.
Answer: False.
Correct : To find whether the charge on a body is positive or negative, an charged electroscope is used. You need a "known" charge on the electroscope to compare and see if the new body's charge makes the leaves open more or close up.
Teacher's Tip: You need a "charged" base to see the difference between + and -.
Exam Tip: "Divergence increase" means similar charge; "Divergence decrease" means opposite charge.

(q) If a negatively charged rod is brought near a negatively charged pith ball electroscope, the pith ball will be stuck with the rod.
Answer: False.
Correct: If a negatively charged rod is brought near a positively charged pith ball electroscope, the pith ball will be stuck with the rod. Like charges (negative and negative) will always push away from each other.
Teacher's Tip: Same charge = Big "Go Away" (Repulsion).
Exam Tip: Repulsion is the only *sure* test of similar charges.

2. Fill in the blanks

(a) Like charges repel while unlike charges attract.
Answer: repel.
This is the fundamental law of electrostatics. It's why two positive rods will fight to stay apart, while a positive and a negative one will snap together.
Teacher's Tip: Similar = Repel; Different = Attract.
Exam Tip: This is the most important "rule" in this whole chapter!

(b) Mercury is a conductor of electricity while pure water is insulator of electricity.
Answer: conductor; insulator.
Mercury is a metal (even though it's liquid), so it has free electrons. Pure water has no ions or minerals to carry electricity, so it blocks the flow completely.
Teacher's Tip: Metals (even liquid ones) are conductors.
Exam Tip: Note that "Pure" or "Distilled" water is an insulator, but normal tap water conducts.

(c) An ebonite rod when rubbed with fur acquires the negative charge.
Answer: negative.
Fur lets go of its electrons easily, and the ebonite rod is happy to take them. This transfer of negative electrons gives the rod its negative charge.
Teacher's Tip: Ebonite rod + Fur = Negative.
Exam Tip: Always state the rod's charge as "negative" when rubbed with fur.

(d) When an uncharged conductor is brought in contact with the disc of a gold leaf electroscope, its leaves will remain unchanged.
Answer: unchanged.
If the body has no charge, it has no electrons to give or take from the electroscope. Therefore, there is no electrical force to move the gold leaves.
Teacher's Tip: No charge = No action.
Exam Tip: If leaves "diverge", the body *must* be charged.

(e) Charge is shared in charging a conductor by the method of conduction.
Answer: conduction.
Conduction is like splitting a pile of coins between two people. By touching, the two objects "share" the total amount of extra charge until they are balanced.
Teacher's Tip: Conduction = Sharing by Touching.
Exam Tip: The final charge is the *same kind* in conduction.

3. Match the following

Column A                                                        Column B
(a) Two like charges                                      (i) negative charge
(b) Two unlike charges                                  (ii) repel
(c) Silver is a                                                 (iii) insulator
(d) Silk is an                                                  (iv) attract
(e) Ebonite rod rubbed with fur acquires       (v) conductor
Answer:
Column A - Column B
(a) Two like charges - (ii) repel
(b) Two unlike charges - (iv) attract
(c) Silver is a - (v) conductor
(d) Silk is an - (iii) insulator
(e) Ebonite rod rubbed with fur acquires - (i) negative charge
These pairs cover the core facts of static electricity. Matching them correctly proves you understand how materials react to heat and friction to produce electrical effects.
Teacher's Tip: Remember "Silver-Conductor" and "Silk-Insulator" as standard pairs.
Exam Tip: Read both columns carefully before drawing lines or writing numbers.

4. Select the correct alternative

(a) When a glass rod is rubbed with dry silk cloth, the charge acquired by the silk cloth is
1. positive
2. negative
3. both positive and negative
4. none of the above
Answer: 2. negative.
As the glass rod is rubbed, it loses electrons to the silk cloth. Since the silk gains extra electrons, it takes on a negative charge.
Teacher's Tip: Glass is (+) so Silk must be (-).
Exam Tip: If the rod becomes positive, the cloth *always* becomes negative because of conservation of charge.

(b) When an ebonite rod is rubbed with fur, the rod acquires
1. positive charge
2. negative charge
3. no charge
4. none of the above
Answer: 2. negative charge.
The friction between ebonite and fur causes electrons to jump from the fur onto the rod. This buildup of negative particles gives the rod its negative charge.
Teacher's Tip: Ebonite = Negative.
Exam Tip: Use this rod to test unkown charges in problems.

(c) When a negatively charged body is brought closer to another negatively charged body, then they will show
1. attraction
2. no effect
3. repulsion
4. none of the above
Answer: 3. repulsion.
Like charges have an invisible electrical force that pushes them away from each other. The closer they get, the stronger this pushing force becomes.
Teacher's Tip: Negative hates Negative.
Exam Tip: "Repulsion" is the word used for objects pushing each other away.

(d) Charging a conductor by bringing another charged conductor close to it without touching is called
1. induction
2. conduction
3. convection
4. radiation
Answer: 1. induction.
Induction uses the force of attraction or repulsion to shift the charges inside a neutral body. No physical contact is needed for this to happen.
Teacher's Tip: Induction = "In-distance" (from a distance).
Exam Tip: "Without touching" is the clue for choosing Induction.

(e) The factor responsible for charging a conductor is
1. transfer of protons
2. transfer of neutrons
3. transfer of electrons
4. transfer of both protons and electrons
Answer: 3. transfer of electrons.
Only electrons can move from one atom to another because they are on the very outside of the atom. Charging something is just the process of gaining or losing these tiny negative particles.
Teacher's Tip: Electrons are the "movable parts" of an atom.
Exam Tip: Never say protons move; only electrons are responsible for charging.

(f) Two objects when rubbed together get charged. The charges on them are
1. equal and opposite
2. equal and similar
3. unequal and similar
4. unequal and opposite
Answer: 1. equal and opposite.
For every electron one object loses, the other object must gain it. This means they will have the exact same amount of charge, but one will be positive and the other negative.
Teacher's Tip: It's a "fair trade" of charges.
Exam Tip: This is called the "Law of Conservation of Charge".

(g) When a glass rod is rubbed with silk, the glass rod and the silk get charged because electrons are transferred from the silk to the glass rod
1. electrons are transferred from the glass rod to the silk
2. protons are transferred from the silk to the glass rod
3. protons are transferred from the glass rod to the silk
Answer: 1. electrons are transferred from the glass rod to the silk.
The silk "pulls" harder on electrons than the glass does. Rubbing provides the energy needed to rip the electrons off the glass atoms and move them to the silk.
Teacher's Tip: The rod loses electrons, so it becomes (+) positive.
Exam Tip: Always link the movement of electrons to the resulting charges (+ for losing, - for gaining).

(h) The conductor of electricity is
1. wood
2. glass
3. ebonite
4. human body
Answer: 4. human body.
While wood, glass, and ebonite are excellent insulators, the human body can carry electricity. This is due to the salty fluids inside our tissues and skin.
Teacher's Tip: Most biological things (like people and trees) conduct because they are "wet".
Exam Tip: List "human body" as a primary biological conductor.

(i) A gold leaf electroscope is to be charged positively by conduction. For this
1. a positively charged rod is held close to near the disc of electroscope
2. a positively charged rod is placed in contact with the disc of electroscope
3. a negatively charged rod is held near the disc of electroscope
Answer: 2. a positively charged rod is placed in contact with the disc of electroscope.
Conduction *requires* physical contact. By touching the positive rod to the disc, positive charges (actually a loss of electrons) spread onto the electroscope.
Teacher's Tip: Contact = Conduction.
Exam Tip: If you want the same charge (+), use conduction (touching).

4. a negatively charged rod is touched with the disc of electroscope

(j) A glass rod rubbed with silk is touched with the disc of a negatively charged gold leaf electroscope. The divergence of leaves will
1. decrease
2. increase
3. remain unchanged
4. first decrease and then increase.
Answer: 1. decrease.
The positive glass rod will neutralize some of the negative charges already on the leaves. Since there is less negative charge, the force pushing the leaves apart gets weaker.
Teacher's Tip: Opposites "cancel out", reducing the push.
Exam Tip: Opposite charges *always* decrease divergence in an electroscope.

(k) The rod in a gold leaf electroscope is made up of
1. wood
2. brass
3. glass
4. ebonite
Answer: 2. brass.
Brass is a metallic conductor that can easily transfer the electrical charges from the top disc down to the delicate gold leaves. It is also strong enough to stay straight inside the glass jar.
Teacher's Tip: Conductors like brass are essential for the rod to work.
Exam Tip: Brass is the most common material for the electroscope rod.

(l) Lightning conductor is made up of:
1. copper
2. glass
3. ebonite
4. wood
Answer: 1. copper.
Copper is used because it is one of the best and most reliable conductors of electricity. It can carry the huge energy of a lightning bolt safely into the ground without melting or catching fire.
Teacher's Tip: Copper is the "super-highway" for lightning.
Exam Tip: Always name "Copper" as the material for lightning rods and grounding wires.

B. Short/Long Answer Questions

Question 1: What do you understand by electricity at rest ?
Answer: When the charges are not allowed to flow are termed as static electricity, i.e., the electricity at rest.
This happens when electrons pile up on the surface of an insulator and stay there because they have no path to travel. It is the "still" version of electricity, unlike the current that flows through your phone charger.
Teacher's Tip: Static = Resting.
Exam Tip: Use the term "Static Electricity" to describe charges at rest.

Question 2: Why does a plastic comb rubbed with dry hair attract bits of paper ?
Answer: Plastic comb rubber with dry hair gets charged and attracts the bits of paper.
The rubbing pulls electrons from your hair onto the plastic comb, making it negatively charged. This charged comb then creates a force that pulls on the neutral paper bits, making them jump up to touch it.
Teacher's Tip: Friction "activates" the comb's charge.
Exam Tip: Mention that the comb becomes "electrically charged" due to rubbing.

Question 3: Who discovered the way of producing electricity by friction?
Answer: Philospher Thales discovered it but it was satisfactorily explained by Dr Gilbert.
Ancient Greeks like Thales noticed that rubbing amber would attract small objects over 2000 years ago. However, it wasn't until hundreds of years later that Dr. Gilbert did the science to explain how it really worked.
Teacher's Tip: Thales found it, Gilbert explained it.
Exam Tip: Mention both names for a more complete historical answer.

Question 4: Name two substances which can be charged by friction.
Answer: (i) Glass. (ii) Ebonite.
These are common materials that hold onto a static charge very well. When you rub glass with silk or ebonite with fur, they become clearly positive or negative.
Teacher's Tip: Plastic and Rubber are also great examples.
Exam Tip: Use "Glass" and "Ebonite" as your standard examples in exams.

Question 5: What are the two kinds of charges ?
Answer: (i) Negative charge. (ii) Positive charge.
Everything in the universe is balanced between these two opposites. Charges can cancel each other out if there are equal amounts of both, making the object "neutral".
Teacher's Tip: Think of them as "Electrical Plus and Minus".
Exam Tip: Use the symbols (+) and (-) alongside the names.

Question 6: A glass rod is rubbed with silk. State the kind of charge acquired by each.
Answer: When a glass rod is rubbed with silk, the glass rod loses electrons to the silk piece. The glass rod has free electrons which are less tightly bound so get transferred to the silk cloth. The glass rod has defeciency of electrons and acquired apositive charge while the silk cloth acquires a negative charge.
The glass rod becomes positive because it gave away some of its negative particles. The silk is like a container that caught those particles, making it negative overall.
Teacher's Tip: Losing (-) makes you (+).
Exam Tip: State both charges: Glass (+) and Silk (-).

Question 7: An ebonite rod is rubbed with fur. State the kind of charge acquired by each.
Answer: EXPERIMENT : TO DEMONSTRATE CHARGES ARE OF TWO KINDS: Take two glass rods A and B and charge each by rubbing them with silk. Take two Ebonite rods C and D and charge each by rubbing with Fur or (flanel) suspend charged rod A by a thread in stand. Bring charged rod B near A. A gets deflected (moves away) This show that A is repelled by B. Now suspend charged rod C in a stand and bring charged rod D ‘ near C. Again repulsion is seen. Now bring charged rod C near the suspended charged rod A. This time attraction is there between the two rods. This prove that charges are of two kinds A and B have same kind of r charge called +ve charge and similar charge repels eachother where as rods C and D also have similar charge (-ve charge) and repel each other. Rod A attracts rod C prove that opposite charges attract each other.
This famous experiment shows that there aren't just "active" and "inactive" rods, but two different types of activity. If everything were the same, all charged rods would repel each other, but the attraction between glass and ebonite proves they are opposites.
Teacher's Tip: Experimenting with multiple rods proves the "Attract/Repel" rules.
Exam Tip: Always conclude that "like charges repel and unlike charges attract".

Question 8: Describe an experiment to demonstrate that there are two kinds of charges.
Answer: Aim - To show that there are two kinds of charges. Apparatus - gold leaf electroscope, glass rod rubbed with silk cloth. any two non-identical bodies say A and B. Procedure -
(i) Charge the gold leaf electroscope positively by touching it with glass rod rubbed with silk cloth.
(ii) The gold leaf electroscope shows its charging by showing its leaves diverging.
(iii) Touch the brass cap of this electroscope with body A-Note the divergence of the gold leaves.
(iv) Now touch the brass cap with body Band note the divergence. Observation - In case of body A - Leaves further diverge. In case of body B - leaves converge. Inference - Body A (positively charged). Body B (negatively charged). So there are two types of charges.
By using an electroscope that is already charged, you can see how new objects affect it. If the leaves spread more, the new object has the same charge; if they move together, it has the opposite charge.
Teacher's Tip: The electroscope acts like a "comparison scale" for charge.
Exam Tip: Use the terms "diverge" (spread) and "converge" (come together) to describe the leaves.

Question 9: How will you show that like charges repel and unlike charges attract each other ?
Answer: Experiment: Take a glass rod rubbed with silk piece (+vely charged) Suspend it in a stand with the help of a thread. Bring a-vely charged Ebonite rod (rubbed with fur) near the glass rod. Attraction is seen between the two rods. Now inter change them i.e. suspend B and bring A near it, again attraction is there. This show that unlike charges attract each other. Now take two glass rods (+vely charged) and bring them near each other, repulsion takes place. Similarly, if we take two -vely charged ebonite rods and suspend one of them and bring second rod near it again the suspended rod moves away showing repulsion between like charges.
This experiment uses simple hanging rods to see which way they swing when a partner is brought close. Seeing them pull together or push apart is the ultimate proof of the fundamental laws of electricity.
Teacher's Tip: Use a thread so the rods can move freely.
Exam Tip: Mention "Unlike charges attract" and "Like charges repel" in your final conclusion.

Question 10: A glass rod rubbed with silk is suspended near an ebonite rod rubbed with fur. What will be your observation ? Give a reason to your answer.
Answer: A glass rod rubbed with silk i.e. +vely charged is brought near ebonite rod rubbed with fur i.e. negatively charged ATTRACTION is seen as they have opposite charge.
Since the glass rod has lost electrons (+) and the ebonite rod has gained them (-), they exert an invisible electrical force on each other. This force pulls them together because they are electrical opposites.
Teacher's Tip: Glass and Ebonite are like a "Plus and Minus" pair.
Exam Tip: Always name the specific charges (+ and -) before stating "Attraction".

Question 11: An ebonite rod rubbed with fur is suspended near another ebonite rod rubbed with fur. State your observation and give a reason to support your answer.
Answer: Both ebonite rods are rubbed fur with have similar charge (-ve charge). We know like charges repel each other.
therefore Rods repel each other. Reason: Like charges REPEL each other.
Since both rods went through the same process with the same material, they both ended up with a buildup of negative electrons. When two negative objects come close, they try to get as far away from each other as possible.
Teacher's Tip: Same method = Same charge = Repulsion.
Exam Tip: "Repulsion" is the definitive test for similar charges.

Question 12: What do you mean by conservation of charges ?
Answer: According to the Law of conservation of charge “When two different bodies are rubbed together, both bodies get charged equally but with charges of opposite kind.” Thus, the total charge of two bodies before and after rubbing remains the same. Example : When an ebonite rod is rubbed with fur, the electrons from the fur are transferred to the ebonite rod and therefore the ebonite rod becomes negatively charged (due to gain of eletrons), while the fur becomes equally positively charged (due to deficit of same number of electrons). As the same no. of electrons are exchanged by the ebonite rod and fur, the magnitude of charges main same but with opposite sign.
Electricity can't be created out of nothing; it is just "moved" from one place to another. If one object gets five extra electrons, the other object must be missing exactly five electrons.
Teacher's Tip: It's like a game of tag - the total number of players never changes, just who is "it".
Exam Tip: State that "Total charge remains constant" for full marks on conservation.

Question 13: An ebonite rod is rubbed with fur. Compare the charges acquired by them.
Answer: An ebonite rod is rubbed with fur the electrons are transferred from fur to ebonite rod. Ebonite has excess of electrons is negatively charged and fur due to deficit of same number of electrons gets positive charge.
The two objects will have exactly equal amounts of charge, just with different signs (+ and -). If you put them back together, they would neutralize each other and become zero again.
Teacher's Tip: Gained electrons = Negative; Lost electrons = Positive.
Exam Tip: Emphasize that the "magnitude" (amount) of charge is identical on both.

Question 14: Name three constituents of an atom and state the kind of charge on each of them.
Answer: The three constituents of an atom are: (i) Protons - These carry positive charge. (ii) Electrons - These carry negative charge. (iii) Neutrons - They have no charge or are electrically neutral.
Atoms are like tiny solar systems where the heavy protons and neutral neutrons are in the center, and the light electrons zip around them. It is the balance of these three that determines if an atom has a charge or not.
Teacher's Tip: Protons are "Positive", Neutrons are "Neutral", and Electrons are "Negative".
Exam Tip: Draw a simple atom diagram with labels to score high marks.

Question 15: What is the net charge on an atom ?
Answer: Net charge on atom is zero i.e. atom is neutral.
Because a normal atom has the exact same number of positive protons as negative electrons, they perfectly cancel each other out. This is why a piece of iron or a glass of water doesn't shock you when you touch it.
Teacher's Tip: Plus five and Minus five equals Zero.
Exam Tip: Use the word "Neutral" to describe an atom with no net charge.

Question 16: Briefly describe the structure of an atom.
Answer: STRUCTURE OF ATOM: Atom has equal number of +ve charge (protons) and -ve charge electrons and hence atom has no charge. Neutrons (having no charge) and protons are present in nucleus. Electrons keep revolving around the nucleus in different shells.
The nucleus is the heavy "heart" of the atom where the protons and neutrons live. The electrons are the "busy bees" that fly around the nucleus in specific paths called orbits or shells.
Teacher's Tip: It's like a sun (nucleus) with planets (electrons).
Exam Tip: Always mention that the nucleus is in the "center" and electrons "revolve" around it.

Question 17: What are free electrons ?
Answer: FREE ELECTRONS. Electrons of the outermost orbit of a solid, which can easily leave the atom and become free to move inside the solid are called FREE ELECTRONS.
In metals, some electrons are not "locked" to their atoms and can wander around between them. These wandering electrons are what carry electric current from one end of a wire to the other.
Teacher's Tip: Free electrons are "unattached" and ready to move.
Exam Tip: Define them as electrons in the "outermost orbit" that can "easily leave" the atom.

Question 18: What causes the charging of two objects when they are rubbed together ?
Answer: CAUSE OF CHARGING OF TWO OBJECTS WHEN RUBBED: Both objects before rubbing are neutral. On Rubbing transfer of electrons from one object to other object takes place. The body from which electrons are transferred gets DEFICIENT in ELECTRONS and becomes POSITIVELY charged. The body to which electrons are transferred has EXCESS ELECTRONS and becomes NEGATIVELY charged.
Charging is essentially just an "electron trade" caused by friction. Friction provides the energy needed to kick electrons off one material and onto another, breaking their original balance.
Teacher's Tip: Rubbing = Electron Transfer.
Exam Tip: Always mention "transfer of electrons" to explain charging.

Question 19: In each of the following cases, state which body loses electrons: (a) A glass rod when rubbed with silk. (b) An ebonite rod when rubbed with fur.
Answer: (a) A glass rod is rubbed with silk. Glass rod loses electrons and becomes positively charged. Silk gains electrons and becomes negatively charged. (b) An Ebonite rod is rubbed with fur. Fur loses electrons and acquires positive charge.
The material that becomes positive is always the "loser" in the electron trade. In these two examples, the glass rod and the fur both give away their electrons, leaving them with a positive charge.
Teacher's Tip: Positive = Loser (of electrons).
Exam Tip: Identify the rod's charge first, then you'll know who lost the electrons.

Question 20: A glass rod is rubbed with silk. Explain the charging of the glass rod and the silk on the basis of electron movement.
Answer: A glass rod is rubbed with silk. Glass rod loses electrons and becomes positively charged. Silk gains electrons and becomes negatively charged. Explanation: Suppose glass rod in neutral form has 10 protons and 10 electrons i.e. 10 units of positive charge and 10 units of negative charge. While silk has (in neutral state) 7 electrons and 7 protons (suppose) i.e. 7 units of negative charge and 7 units of positive charge. Suppose on rubbing together glass rod loses 2 electrons and silk gains 2 electrons. Now glass rod has 8 electrons and 10 protons on it. i.e. 8 units of negative charge and 10 units of positive charge i.e. glass rod has net 2 units of positive charge. Thus, glass rod has acquired positive charge. Silk has now 9 units of negative charge and 7 units of positive charge i.e. silk has net 2 units of negative charge. Thus, silk has acquired negative charge.
This "math" explanation shows how the charge is perfectly conserved. No protons are moved; we only change the "negative" count, which automatically creates a net charge on both objects.
Teacher's Tip: Use a "Number Line" to see how losing negatives makes you more positive.
Exam Tip: Use a numerical example (like 10 protons/10 electrons) to make your explanation clearer.

Question 21: An ebonite rod is rubbed with fur. Explain the charging of the ebonite rod and the fur on the basis of electron movement.
Answer: An Ebonite rod is rubbed with fur. Ebonite rod gains electrons and acquires negative charge while fur loses electrons and acquires positive charge. Explanation. Same as in the above question.
Just like with glass and silk, rubbing ebonite and fur causes electrons to jump from one to the other. In this specific case, the ebonite rod is the "winner" that gains extra electrons, leaving the fur positive.
Teacher's Tip: Ebonite rod always ends up negative (-).
Exam Tip: State clearly that "electrons move from fur to ebonite rod".

Question 22: Distinguish between conductors and insulators of electricity.
Answer: DISTINCTIONS BETWEEN CONDUCTORS AND INSULATORS OF ELECTRICITY:
CONDUCTORS:
(i) They allow the current electricity to flow through them.
(ii) They have large number of free electrons.
(iii) All metals like Ag, Cu, iron, gold, wet wood etc.
(iv) Conductors cannot be charged by rubbing.
INSULATORS:
(i) Do not allow the current electricity to flow through them.
(ii) They have small number of free electrons.
(iii) Cotton, dry wood, rubber, glass distilled water etc.
(iv) Can be charged by rubbing.
Conductors are like open hallways where electrons can run freely, while insulators are like brick walls that block them. This difference is why we make wires from metal and cover them in rubber or plastic.
Teacher's Tip: "Conductors Carry, Insulators Inhibit".
Exam Tip: Mention "free electrons" as the key scientific difference between the two.

Question 23: Give one example each of a conductor and an insulator of electricity.
Answer: EXAMPLE of CONDUCTOR: Hydrochloric acid INSULATOR: Mica.
Even liquids can be conductors if they have acids or salts in them. Mica is a natural mineral that is such a good insulator that it's often used in high-voltage industrial machines.
Teacher's Tip: Metals are common conductors, but acids work too!
Exam Tip: "Copper" and "Rubber" are the most common textbook examples.

Question 24: State two ways of charging a conductor.
Answer: The two methods of charging a conductor are: (a) Conduction - The process of charging an uncharged conductor by touching with a charged conductor, the uncharged conductor shares the charge of the charged conductor. (b) Induction - The process of charging an uncharged conductor with a charged conductor, without actually touching it is called induction. Here the nearer end of the uncharged conductor acquires a charge of Opposite nature as compared to the charge on a charged conductor.
Conduction is like transferring a flame by touching one candle to another. Induction is more like a magnet pulling paperclips; you influence the other object's charges just by being near it.
Teacher's Tip: Conduction = Contact; Induction = Influence.
Exam Tip: Highlight "Touching" vs "Without Touching" to distinguish between them.

Question 25: Name the way of charging a conductor in which the charge is shared.
Answer: By conduction.
Because the two objects are physically touching, the extra electrons can flow across the contact point. This flow continues until both objects have a similar density of charge.
Teacher's Tip: Conduction = Sharing.
Exam Tip: Conduction is the *only* method where the two objects end up with the same type of charge.

Question 26: Describe the method of charging a conductor by conduction.
Answer: Conduction - The process of charging an uncharged conductor with a charged conductor by touching the uncharged one. Here the uncharged conductor shares the charge of the charged conductor. Method of charging - Mount the uncharged conductor on an insulating stand take the charged conductor with an insulating handle to the uncharged conductor. If the charged conductor is positively charged then the uncharged will be charged positive and if the charged is negatively charged then the uncharged will be negatively charged.
To charge by conduction, you must hold the charged rod by its handle and literally "paint" the charge onto the neutral metal object. Once you pull the rod away, the metal object keeps some of that charge for itself.
Teacher's Tip: Use an "Insulating Stand" so the charge doesn't leak into the ground.
Exam Tip: Mention that the final charge is of the "Same Kind" as the charging body.

Question 27: A metal rod A is to be charged positively by using another charged rod B. What should be the kind of charge on the rod B if charging is to be done by conduction ?
Answer: Rod A is uncharged and Rod B is charged body. A is to be charged positively by touching i.e. by conduction. So rod / B should have similar charge as is required by A i. e. +vely. So rod B should be positively charged, therefore By conduction same kind of charge is produced and shared by uncharged body.
Conduction is a "copy-paste" method for electricity. If you want the new object to be positive, your "charging tool" must also be positive because they are going to share the same resource.
Teacher's Tip: "Like follows Like" in conduction.
Exam Tip: Always state that conduction results in "similar charge".

Question 28: Explain the charging by conduction in terms of movement of electrons.
Answer: CHARGING A CONDUCTOR BY CONDUCTION: Place rod A on an insulating stand and bring a +vely charged conductor B near A and touch it. Charge from B is transferred on A till charge on both of them is same. Remove conductor B. A gets charged positively. Explaination on the bases of electrons : Suppose body A (neutral rod) has 10 protons and 10 electrons. Body B is positively charged is deficient in electrons has 20 electrons and 30 protons. On touching B with A, 5 electrons are transferred from A to B. Now B is +vely charged as B has 25 protons and 25 electrons. A is also +vely charged as A has 15 protons and 10 electrons. therefore A and B each has, 5 protons in excess and have +5 charge. (Note: Textbook text says "protons are transferred", but correctly it should be electrons as per the numerical explanation below).
In conduction with a positive rod, the rod actually "sucks" electrons out of the neutral body. This leaves the neutral body with fewer electrons than protons, making it positively charged too.
Teacher's Tip: Electrons move *toward* the positive rod to balance it.
Exam Tip: Correct the theory if needed: *Only electrons move* during the process, even if the result is positive.

Question 29: Describe the method of charging a conductor by induction.
Answer: INDUCTION: “Charging an uncharged conductor by bringing a charged conductor near it without touching is called INDUCTION. Place uncharged conductor B near +vely charged conductor A nearer end of B has -vely charged electrons attracted towards +vely protons remain on farther end of B. Hence, nearer end of B is charged oppositely i.e. negative. We can test it by pith ball electroscope. On removing charged body A away from B, The body B becomes neutral due to protons and electron in B are equal and have opposite charge.
Induction is a temporary "charge separation". It's like the positive rod acts as a magnet that pulls all the negative electrons to the front of the object, leaving the back end positive. If you move the rod away, everything just mixes back together and the object becomes neutral again.
Teacher's Tip: Induction = Temporary separation without contact.
Exam Tip: The "near end" is always charged *oppositely* to the charging rod.

Question 30: Explain the charging by induction in terms of movement of electrons.
Answer: Let uncharged conductor B mounted on insulated stand is placed near +vely charged conductor A mounted on insulated stand without touching. Electrons which are equal in number of protons in uncharged B, are attracted towards +vely charged A. Hence end E is charged negatively called BOUND CHARGE and protons remain at end F of B and is positively charged called FREE charge: This induced charge remains on B so long as body A remains near B.
When the positive rod comes close, the free electrons in the metal body are "invited" to gather at the front end. They are called "bound" because they are held there by the rod's attraction. The positive charges left at the back are "free" because they aren't directly being pulled by the rod.
Teacher's Tip: Bound charges are "stuck", free charges are "loose".
Exam Tip: Define "Bound Charge" (closer end) and "Free Charge" (farther end) clearly.

Question 31: Figure below shows a metal rod AB placed on an insulating stand. In figure (a) a negatively charged ebonite rod C is touched with the metal rod AB, while in figure (b), the negatively charged ebonite rod C is held near the rod AB. State the kind of charges at the ends A and B of the rod, in each case.
Answer: In figure (a) conduction takes place. There is negative charge at both ends A and B. In figure (b) Induction takes place. End A has oppositely positive charge called Bound charge and End B is similarly charged i.e. negative free charge.
Touching makes the whole rod one big negative object (conduction). Holding the rod nearby just pushes the negative charges to the far end, leaving the near end positive (induction).
Teacher's Tip: (a) = Same everywhere; (b) = Opposites at ends.
Exam Tip: Induction always results in two different charges at the two ends of the conductor.

Question 32: Can you charge an insulator by the method of conduction ?
Answer: No, we cannot charge an insulator by method of conduction.
Because insulators don't have free electrons that can easily move around, touching them with a charged rod won't spread the electricity across their whole surface. The charge would just stay stuck at the tiny point where they touched.
Teacher's Tip: Conduction needs "flow", which insulators don't have.
Exam Tip: Mention "lack of free electrons" as the reason insulators can't be charged by conduction.

Question 33: What is an electroscope ? Name the two types of electroscopes.
Answer: An electroscope is a device with the help of which we detect whether the body is charged or uncharged and in the charged body detects the type of charge it carries. i.e. whether positive or negative. The electroscope are of two types. (i) Pith ball electroscope. (ii) Gold leaf electroscope.
An electroscope is like a "sixth sense" for electricity. It uses physical movement (like a swinging ball or opening leaves) to tell us if there is invisible static electricity nearby.
Teacher's Tip: It's a "Charge Detector".
Exam Tip: Name both "Pith ball" and "Gold leaf" types to get full marks.

Question 34: Describe a pith ball electroscope. how can you use it to test whether a body is charged or uncharged ?
Answer: PITH BALL ELECTROSCOPE It consists of a smail pith ball suspended by a dry silk thread from an insutating stand. TO TEST A BODY IS CHARGED OR NOT: Bring the body to be tested near the pith ball (without touching it). If the pith ball moves towards the body, the body is charged. But if the body does not move, the body is uncharged.
The pith ball is so light that even a tiny amount of static electricity can pull it toward another object. This movement is a simple "Yes/No" signal for the presence of an electrical charge.
Teacher's Tip: Pith is a very light, sponge-like material.
Exam Tip: Specify that you should not touch the ball to test for just the *presence* of charge.

Question 35: How will you use a pith ball electroscope to find out whether the charge on a charged body is positive or negative ?
Answer: Take a positively charged pith ball electroscope. Bring the charged body near the pith ball (without touching it). If the pith ball moves away, the body has similar charge (positive charge) and if the pith ball moves towards the body, the body has negative charge.
To find the "kind" of charge, you first have to give the pith ball a known charge (like +). Then, if a new object pushes the ball away, it must also be (+), but if it pulls it in, it must be the opposite (-).
Teacher's Tip: "Repel = Same; Attract = Different".
Exam Tip: You *must* use a pre-charged pith ball to test for the type of charge (+ or -).

Question 36: Draw a labelled diagram of a gold leaf electroscope and describe its construction.
Answer: Construction: (i) Brass rod which passes through an insulator stopper in a glass case.
(ii) Brass disc is at the top end of brass rod.
(iii) Gold leaves Lower end carries two gold (or aluminium) leave held parallel when uncharged.
(iv) Glass case protects the gold leaves from the outside air current.
(v) Metal foil present at the lower part of the glass case. This is connected to the earth when the electroscope is used.
The gold leaf electroscope is very delicate; it uses incredibly thin sheets of gold that are so light they can feel the push of even a single electron. The glass jar is there to keep out wind and dust that might accidentally move the leaves.
Teacher's Tip: Gold is used because it can be hammered into very, very thin leaves.
Exam Tip: Label the "Brass Disc", "Insulator", and "Gold Leaves" in your diagram.

Question 37: A positively charged glass rod is touched with the disc of an uncharged gold leaf electroscope. What will be your observation?
Answer: Leaves will DIVERGE as both leaves have positive charge due to conduction and diverge as like charges REPEL EACH other.
When you touch the disc, the positive charge spreads down the brass rod and into both gold leaves. Since both leaves now have the same positive charge, they try to get away from each other and pop open like a "V".
Teacher's Tip: Touching = Diverging.
Exam Tip: "Divergence" is the correct term for the leaves spreading apart.

Question 38: How will you use a gold leaf electroscope to find out whether a body is charged or uncharged ?
Answer: TO TEST IF THE BODY is CHARGED OR UNCHARGED with GOLD LEAF ELECTROSCOPE: The body to be tested for charged or not is brought near the disc of G.L.E. and touched with disc. If the leaves diverge, the body is charged and if leaves are not diverged, it is uncharged.
If an object has no charge, nothing happens to the leaves because there is no electrical force. Any amount of charge, whether positive or negative, will always cause the neutral leaves to open up at least a little bit.
Teacher's Tip: No movement = Neutral object.
Exam Tip: "Touching the disc" is the standard test for simple detection.

Question 39: How will you use a gold leaf electroscope to find out whether the charge on a charged body is positive or negative ?
Answer: (a) Charge negatively the gold leaf electroscope by conduction i.e. To detect the kind of charge by a positively charged gold leaf electroscope touching the disc of G.L.E. with -vely charged ebonite rod. The leaves diverge (because of repulsion) Note the divergence as show in figure (a).
(b) Bring a charged body to be tested in contact with disc. If divergence in leaves increase, it has similar charge i.e. negative as shown in figure (b).
(c) If divergence decrease, the body has opposite charge i.e. positive charge as shown in figure (c).
Just like with the pith ball, you need to "pre-load" the electroscope with a charge you already know. Then, you watch if the new object makes the "V" shape bigger (similar charge) or smaller (opposite charge).
Teacher's Tip: "Increase = Same; Decrease = Opposite".
Exam Tip: Mention that you start with a "known charged electroscope" to find the type of charge.

Question 40: A negatively charged ebonite rod is touched with the disc of a negatively charged gold leaf electroscope. What will be your observation ?
Answer: Divergence of leaves will increase because similar charge will increase.
By touching it with another negative rod, you are adding even more negative electrons to the leaves. More charge means a stronger repulsive force, so the leaves push each other open even wider.
Teacher's Tip: More of the same = More push.
Exam Tip: State that "divergence increases" for same charges.

Question 41: When a charged rod is touched with the disc of a positively charged gold leaf electroscope, it is observed that the divergence of leaves decreases. What is the kind of charge on the rod ?
Answer: As on touching the disc with charged rod, divergence in the leaves decreases, this means the rod has opposite kind of charge than leaves i.e. rod has negative charge.
The negative charges from the rod cancel out some of the positive charges on the leaves. With less total charge on the leaves, they don't repel each other as hard, and they start to fall back together.
Teacher's Tip: Decrease = Opposite charge.
Exam Tip: "Reduction in divergence" is the definitive test for an opposite charge.

Question 42: Describe Franklin’s experiment. What did he conclude from his experiment ?
Answer: FRANKLIN’S EXPERIMENT: Franklin flew a kite made of silk in a thunder-storm. At the top comer of the kite, he fixed a metal wire about 30 { cm} long. The other end of the wire was joined to the string. At the lower end of the string he tied a metal key. When the string got wet, he obtained a number of sparks between his Knuckle and the key. He concluded from his experiment that in a thunder storm, the clouds acquire an electric charge due to friction.
This was a very dangerous but famous experiment that proved lightning wasn't magic, but actual electricity. The wet string allowed the static electricity from the clouds to flow down to the key, creating sparks that Benjamin Franklin could see.
Teacher's Tip: Don't try this at home - Ben was lucky he didn't get a fatal shock!
Exam Tip: Mention "friction between clouds" as Franklin's key conclusion.

Question 43: What causes lightning ?
Answer: Due to friction from winds, clouds rub each other and get electrically charged during thunder storm (bundles of small water droplets and ice particles form thunder storm). The upper part of cloud is usually positive while the lower part of cloud gets usually negatively charged. Sudden movement in cloud causes this electrical charge to discharge in the form of LIGHTNING (DAZZLING LIGHT).
Inside a storm cloud, ice and water bits are constantly bumping and rubbing together, which builds up a massive amount of static electricity. When the difference between the (+) top and (-) bottom gets too big, a huge spark jumps across the sky - that's lightning!
Teacher's Tip: A cloud is like a giant, floating battery.
Exam Tip: Use the term "Electric Discharge" to describe the final spark.

Question 44: What are the effects of lightning ?
Answer: EFFECTS OF LIGHTINING: Lightning can kill the men, animals and shatter the buildings.
Lightning is incredibly powerful and carries a huge amount of heat and electrical energy. It can blow apart stone walls, set trees on fire, and stop a person's heart instantly if it hits them.
Teacher's Tip: Lightning is faster and hotter than the surface of the sun!
Exam Tip: List at least two destructive effects like "death of living beings" and "damage to property".

Question 45: What is a lightning conductor ? How does it work ?
Answer: The conductor which is fixed on the top of the building to protect the buildings from the damage by lightning. The conductor consists of several sharp metal spikes connected to a thick copper strip. The other end of the copper strip is fixed to a metal plate buried inside the ground. The process is called earthing. The conductor works on the principle of induction. Whenever a charged cloud pass by the building, the conductor gets charge opposite to that of the cloud through the process of induction. Now this acquired charge moves to the earth through the earthing system.
The sharp spikes on top "leak" charges into the air to try and neutralize the cloud before it can strike. If the cloud does strike, the thick copper wire acts like a designated highway for the electricity to go straight into the ground without touching the building.
Teacher's Tip: It's an "Early Warning" and a "Safety Path" all in one.
Exam Tip: Mention "induction" and "earthing" as the two key scientific processes.

Question 46: How is a tall building protected from damage due to lightning?
Answer: We can protect a tall building from lightning by the use of LIGHTNING CONDUCTOR.
By installing a copper rod higher than the rest of the roof, we ensure that lightning hits the rod instead of the building. The rod then guides the power safely into the dirt through a heavy cable.
Teacher's Tip: Tall buildings are the biggest targets for lightning.
Exam Tip: "Lightning Conductor" is the specific tool name you must use.

Question 47: State three safety measures that you will observe in thunder storm.
Answer: THREE SAFETY MEASURES DURING THUNDER STORM:
(i) Do not lie on the ground, but squat low on the ground with your hands on you knees and head in between.
(ii) Take out the plugs of the T.V. sets, computers, etc. Do not use the wired phone.
(iii) Do not take bath during the thunder storms and avoid contact with running water or metallic tap.
(iv) Do not carry an umbrella over your head particularly if walking in an open ground. If there are tree around, take shelter under a shorter tree.
Staying safe in a storm means staying away from anything that "conducts" or "attracts" electricity. Metal pipes, wires, and tall trees are all dangerous, and the safest place to be is inside a house or a car.
Teacher's Tip: "When Thunder Roars, Go Indoors!"
Exam Tip: Memorize three distinct points (like unplugging electronics, avoiding water, and not using umbrellas) to be safe.