Selina Concise Solutions for ICSE Class 7 Physics Chapter 7 Electricity and Magnetism

Points to Remember

• Some materials behave in a particular manner showing magnetic properties.
• A freely suspended bar magnet always point in North-South direction.
• Like poles repel each other while unlike poles attract each other.
• Magnet is neutral at its centre and has maximum magnetic effects at its ends called the poles.
• Poles always exist in pairs with opposite polarities and can never be isolated.
• Examples of magnetic substances are - iron, cobalt, nickel.
• Examples of non-magnetic substances are - wood, plastic, aluminium, copper.
• The poles are not exactly the ends of the magnet but they are slightly inside.
• For a given magnet, both the poles are of equal strength.
• Earth’s magnet has its south pole situated near the geographic north.
• Electromagnets are the temporary magnets which are made up of soft iron core with a winding of insulated copper wire.
• Freely suspended current carrying solenoid always rests in north- south direction.
• A direct current source has the fixed positive and negative terminals, e.g. a battery.
• Hans Christian Oersted discovered that if an electric current is passed through a conductor, a magnetic field is developed around it.
• The study of magnetic effects produced due to electric current is known as electromagnetism.
• The direction of magnetic field due to a straight current carrying conductor is obtained by any of the following rules:
  (a) Right Hand Thumb Rule.
  (b) Right Hand Cork Screw Rule.
• The property due to which a changing magnetic field within a closed conducting coil induces electric current in the coil is called electromagnetic induction.
• The current produced in a closed coil when magnetic lines of force rapidly change within it is called the induced current.
• The symbol for alternating current is sim.
• The strength of induced current can be increased by increasing the
  (a) the number of turns in the coil
  (b) strength of the magnet used
  (c) relative speed between the magnet and closed coil.
• We cannot think of modern life without electricity. We light our homes and other places of work with electricity.
• It is used to run electric fans, televisions, geyser, electric irons, room heaters, refrigerators, music system etc.
• Cell is a primary source of electricity. A combination of two or more cells is a battery.
• Some other sources of electricity are generator and solar cells.
• The path along which an electric current flows is called a circuit.
• Electricity has the following effects
  (a) Heating effect
  (b) Magnetic effect
  (c) Chemical effect
  (d) Mechanical effect
• When an electric path is complete is called closed circuit and the path with a break is called open circuit.
• The substances which allow the electricity to flow through them are called conductors, e.g. metals, human body etc.
• The substances which do not allow electricity to flow through them are called insulators, e.g. wood, paper, glass etc.
• The consumption of electricity is calculated from the meter in kWh.
• Electric fuse is a device which limits the current in an electric circuit.
• All electrical appliances are connected in parallel in household circuits.
• We should be cautious in using electricity. Certain precautions should be taken before working on an electrical gadget or circuit.

Activity 6

List five such electrical gadgets in your house in which electromagnet is used.
1. Computer
2. Electric motor
3. Fan, Toaster
4. Refrigerator
5. Television
6. Electric Bell
Answer: 1. Computer, 2. Electric motor, 3. Fan, Toaster, 4. Refrigerator, 5. Television, 6. Electric Bell.
Electromagnets are found in devices that use motors or require a temporary magnetic pull to function. They allow us to control magnetism simply by turning the electrical power on or off.
Teacher's Tip: If a device has a spinning motor inside, it almost certainly contains an electromagnet!
Exam Tip: Mention the "Electric Bell" as it is the most common example used for explaining how electromagnets work in exams.

Activity 9

Test material - State of the bulb - Conductor or insulator
Plastic - Does not glow - Insulator
Copper - Glows - Conductor
Eraser (Rubber) - Does not glow - Insulator
Matchstick (wood) - Does not glow - Insulator
Pencil lead (graphite) - Glows - Conductor
Answer: As per the table above, materials like copper and graphite allow current to pass, while plastic, rubber, and wood block it.
Conducting materials complete the circuit path, allowing energy to reach the bulb filament. Insulators create a gap in the electron flow, preventing the bulb from lighting up.
Teacher's Tip: Remember that "Graphite" is a rare non-metal that behaves like a metal conductor.
Exam Tip: Always label a material as a conductor if the bulb "glows" in a circuit test diagram.

Test Yourself

A. Objective Questions

1. Write true or false for each statement

(a) A current carrying coil when suspended freely can rest in any direction.
Answer: False.
A current-carrying coil creates its own magnetic field and behaves just like a bar magnet. Because of this, it will always align itself with the Earth's North-South magnetic axis.
Teacher's Tip: Think of a current coil as a "ghost magnet" that follows the same rules as a solid bar magnet.
Exam Tip: If a statement says "any direction" regarding magnets or solenoids, it is usually false because of Earth's magnetic field.

(b) A coil carrying current behaves like a magnet.
Answer: True.
When electricity flows through a wire, it generates a magnetic field around it, and coiling the wire concentrates this field. This is the core principle behind the creation of electromagnets used in heavy machinery.
Teacher's Tip: The magnetic effect only lasts as long as the electricity is flowing.
Exam Tip: Use the term "electromagnetism" to describe this specific behavior in long-answer questions.

(c) In an electromagnet, the core is made up of copper.
Answer: False.
Copper is used for the wire because it is a great conductor, but the core must be a magnetic material like soft iron. Soft iron is used because it gains and loses magnetism very quickly when the current is switched.
Teacher's Tip: Iron "concentrates" the magnetic lines of force, making the magnet stronger.
Exam Tip: Always specify "Soft Iron" as the core material to score full marks.

(d) An electric bell uses an electromagnet.
Answer: True.
The electromagnet in the bell pulls an iron strip (armature) to hit a gong and make a sound. This mechanical movement is controlled entirely by the magnetic pull created by the current.
Teacher's Tip: The bell rings because the electromagnet rapidly "grabs" and "releases" the metal hammer.
Exam Tip: Label the electromagnet in any diagram of an electric bell you are asked to draw.

(e) An electromagnet with soft iron core is a temporary magnet.
Answer: True.
A temporary magnet is one that only shows magnetic properties while an external force, like electricity, is applied. As soon as you turn off the switch, the soft iron core loses almost all of its magnetic pull.
Teacher's Tip: "Temporary" means it works only while the power is ON.
Exam Tip: Contrast temporary electromagnets with "Permanent magnets" which stay magnetic forever.

(f) We use cell as the source of electricity to run an electric immersion rod.
Answer: False.
An immersion rod requires a huge amount of electrical energy to heat up water, which a small cell cannot provide. Instead, these heavy appliances must be plugged into the high-voltage "mains" supply of the house.
Teacher's Tip: Cells are for small things like clocks; the Wall Socket (Mains) is for big heaters.
Exam Tip: Mention that high-power devices need "mains electricity" because of the high energy requirement.

(g) A torch bulb glows if the terminals of the bulb are connected to the terminals of a cell by the metallic wire.
Answer: True.
Completing this connection creates a closed circuit path for electrons to flow from the cell through the bulb's filament. The resistance in the filament then turns this electrical energy into light and heat.
Teacher's Tip: A circuit must be a "unbroken circle" for the bulb to light up.
Exam Tip: Ensure you specify that the wire must be a "conductor" for this to work.

(h) Wool is a conductor of electricity.
Answer: False. Wool is a insulator of electricity.
Wool does not have free electrons to carry an electric charge from one point to another. Because of this, electricity cannot flow through it, making it safe to use around low-voltage items.
Teacher's Tip: Most non-metals like wool, plastic, and rubber are insulators.
Exam Tip: If a material doesn't let a bulb glow in a circuit, it is an insulator.

(i) Silver is an insulator of electricity.
Answer: False. Silver is good conductor of electricity.
Silver is actually the best conductor of electricity among all metals because it allows electrons to move with very little resistance. However, copper is used more often because it is much cheaper than silver.
Teacher's Tip: Silver is the "King of Conductors"!
Exam Tip: Don't get confused by the price; silver is a better conductor than even copper.

(j) Our body is a conductor of electricity.
Answer: True.
The human body contains a lot of water and salts, which allow electric current to pass through it. This is why we can get an electric shock if we touch a live wire without protection.
Teacher's Tip: Your body is mostly water, and salty water is a great conductor.
Exam Tip: Use the conductivity of the human body to explain why we should never touch switches with wet hands.

(k) For a circuit to be complete, every part of it must be made up of conductors.
Answer: True.
Even one tiny piece of insulator in the main path will act like a wall, stopping the entire flow of electricity. A "complete" circuit means there is a continuous conducting path from the positive to the negative terminal.
Teacher's Tip: Think of a circuit like a train track; if one rail is missing, the train stops.
Exam Tip: Use the term "closed circuit" to describe a complete path made of conductors.

(l) All metals are conductors of electricity.
Answer: True.
The atomic structure of metals includes "free electrons" that can drift throughout the material when a voltage is applied. This common property is why wires are always made of some type of metal.
Teacher's Tip: Metals "share" their electrons easily, which is what makes current flow.
Exam Tip: If asked for a list of conductors, any metal you name will be a correct answer.

(m) The switch should not be touched with wet hands.
Answer: True.
Water, especially when it contains impurities, is a good conductor that can create a path for electricity to reach your skin. This significantly increases the risk of a dangerous or even fatal electric shock.
Teacher's Tip: Water + Electricity = Danger!
Exam Tip: This is a "Safety Precaution" question; always link it to the risk of electric shock.

(n) A switch is an on-off device in an electric circuit.
Answer: True.
The switch works by physically moving a conductor to either complete the circuit (ON) or create an air gap (OFF). This gives us a convenient way to control when we want an appliance to use energy.
Teacher's Tip: "ON" means the circuit is closed; "OFF" means the circuit is open.
Exam Tip: Draw the "key" symbol to represent a switch in circuit diagrams.

2. Fill in the blanks

(a) A magnet has ________ poles.
Answer: two.
Every magnet, no matter how small, has a North pole and a South pole. These poles are the regions where the magnetic force is at its strongest.
Teacher's Tip: You can't have a magnet with just one pole; they always come as a pair.
Exam Tip: If you break a magnet in half, you get two smaller magnets, each with TWO poles.

(b) Like poles ________ each other and unlike poles ________.
Answer: repel, attract.
This is the fundamental law of magnetism where same poles push away from each other and different poles pull together. This behavior is similar to how electric charges interact.
Teacher's Tip: Remember: "Likes don't like each other!"
Exam Tip: Use "Repulsion" and "Attraction" as the formal scientific terms.

(c) An electromagnet is used to separate large mass of ________ scrap.
Answer: iron.
Because iron is a magnetic material, giant electromagnets on cranes can easily pick it up while leaving non-magnetic materials like wood or plastic behind. This is a very efficient way to sort waste in junkyards.
Teacher's Tip: Electromagnets are great because you can drop the scrap just by turning the power off.
Exam Tip: "Iron" and "Steel" are both acceptable magnetic materials for this answer.

(d) The strength of magnetic field of an electromagnet is increased by inserting a core of soft ________.
Answer: iron.
Iron atoms align with the magnetic field of the coil, effectively adding their own magnetic strength to the overall magnet. Soft iron is preferred specifically because it doesn't stay magnetic once the current is removed.
Teacher's Tip: The core is like an "amplifier" for the magnetism.
Exam Tip: Always include the word "Soft" before iron for technical accuracy.

(e) In a torch we use ________ cell as the source of electricity.
Answer: dry.
Dry cells contain chemicals in a paste form, which makes them leak-proof and portable for devices like flashlights. They convert stored chemical energy into the electrical energy needed to light the bulb.
Teacher's Tip: "Dry" just means the chemicals aren't a sloshing liquid like in a car battery.
Exam Tip: The standard AA or D-sized batteries we use are all examples of dry cells.

(f) To light a table lamp and to run a refrigerator, we use ________ as the source of electricity.
Answer: mains.
Mains electricity is the high-power supply provided by power plants to our homes through wall sockets. It provides a steady flow of high-voltage energy that small batteries simply cannot match.
Teacher's Tip: "Mains" is the "big power" from the wall.
Exam Tip: Contrast mains electricity with "Cell" power for high-energy versus low-energy devices.

(g) A group of two or more cells is called a ________.
Answer: battery.
Connecting cells together allows us to combine their voltages to power more demanding electronics. Most gadgets actually use a battery (multiple cells) rather than just a single cell.
Teacher's Tip: One unit = Cell; Many units = Battery.
Exam Tip: Draw multiple cell symbols connected in a line to represent a battery.

(h) ________ pass electricity through them.
Answer: Conductors.
Conductors are materials like metals that allow the flow of electric charges with very little difficulty. They are the essential "roads" that carry electricity from the source to our lights and fans.
Teacher's Tip: Think of "C" for Conductors that Carry current.
Exam Tip: Provide an example like "Copper" if the question asks for a definition of conductors.

(i) ________ do not pass electricity through them.
Answer: Insulators.
Insulators are materials that hold onto their electrons tightly, preventing any current from moving through. We use insulators like plastic coating on wires to handle them safely without getting shocked.
Teacher's Tip: Think of "I" for Insulators that Interruption the flow.
Exam Tip: Name "Plastic" or "Rubber" as common household insulators.

3. Match the following
Column A
(a) Human body
(b) Silk thread
(c) Charge in motion
(d) Soft iron
(e) Electromagnet
Column B
(i) electric bell
(ii) current
(iii) conductor
(iv) electromagnet
(v) insulator
Answer:
Column A - Column B
(a) Human body - (iii) conductor
(b) Silk thread - (v) insulator
(c) Charge in motion - (ii) current
(d) Soft iron - (iv) electromagnet
(e) Electromagnet - (i) electric bell
(a)-(iii), (b)-(v), (c)-(ii), (d)-(iv), (e)-(i).
This exercise connects physical materials and concepts to their specific roles in science. For example, silk is an insulator that blocks electricity, while the movement of charges is what we technically call an electric current.
Teacher's Tip: To match "Soft iron" correctly, remember it is the heart of an electromagnet.
Exam Tip: When matching, draw straight lines and check that no two items from Column A go to the same item in Column B.

4. Select the correct alternative

(a) A freely suspended magnet rests in
1. east-west direction
2. north-south direction
3. north-east direction
4. north-west direction.
Answer: 2. north-south direction.
The Earth acts as a giant magnet, and its magnetic poles pull on the suspended magnet until it aligns with them. This consistent behavior is what makes a magnetic compass such a reliable tool for navigation.
Teacher's Tip: Every compass works because a magnet always wants to point North.
Exam Tip: Mention the "Earth's magnetic field" as the reason for this alignment.

(b) Electromagnets are made up of
1. steel
2. copper
3. brass
4. soft iron.
Answer: 4. soft iron.
Soft iron is chosen because it magnetizes and demagnetizes instantly when current starts or stops. Steel would become a permanent magnet after a while, which would ruin the "on-off" function of an electromagnet.
Teacher's Tip: "Soft" in science doesn't mean squishy; it means it loses magnetism easily.
Exam Tip: Don't pick copper; copper is the wire *around* the core, not the core itself.

(c) An electromagnet is used in
1. electric oven
2. ammeter
3. electric bell
4. radio set.
Answer: 3. electric bell.
The electric bell relies on the mechanical pull of an electromagnet to move the hammer that strikes the bell. Without the magnetic pull, the bell would remain silent despite the electricity flowing.
Teacher's Tip: The bell is the most "famous" school example of an electromagnet in use.
Exam Tip: You can also use "crane" or "relay" as other common answers for where electromagnets are used.

(d) The purpose of armature in an electric bell is
1. to make and break the circuit
2. to produce sound
3. to produce magnetic field
4. to provide spring action.
Answer: 1. to make and break the circuit.
As the armature is pulled toward the magnet, it moves away from a contact screw, which opens (breaks) the circuit. When the magnet turns off, the armature springs back, re-connecting (making) the circuit again.
Teacher's Tip: The armature is the "moving switch" inside the bell.
Exam Tip: Use the phrase "automatic switching" to describe the armature's role.

(e) In a torch, the source of electricity is
1. the bulb
2. the switch
3. the cell
4. the mains.
Answer: 3. the cell.
The cell is the "energy container" that provides the power for the torch to operate. The bulb uses the power, and the switch controls it, but the cell is the actual source.
Teacher's Tip: A source is where the "push" (voltage) starts.
Exam Tip: Distinguish between the "source" (cell) and the "load" (bulb).

(f) Electricity can flow through
1. wood
2. rubber
3. plastic
4. copper wire.
Answer: 4. copper wire.
Copper wire is a metal conductor, meaning it has the free electrons required for electric current to travel. Wood, rubber, and plastic are all insulators that block current from moving.
Teacher's Tip: Copper is used for almost all the wiring in your house because it's so good at this.
Exam Tip: Always pick the metal option in a "flow through" question.

(g) Electricity does not flow through
1. human body
2. animals body
3. rubber
4. silver.
Answer: 3. rubber.
Rubber molecules hold onto their electrons so tightly that they cannot drift and form a current. This is why electricians wear rubber gloves for safety—to stop electricity from passing through them.
Teacher's Tip: Rubber is the ultimate "safety shield" against electricity.
Exam Tip: If the question asks what "does not" flow, look for the best insulator on the list.

(h) We should not touch the switch with wet hands otherwise
1. electricity may pass through our body
2. electricity may not pass through the appliance
3. circuit may break
4. the switch may get off.
Answer: 1. electricity may pass through our body.
Wet skin has much lower resistance to electricity, meaning current can easily enter and travel through your internal organs. This flow through the body causes painful and dangerous electric shocks.
Teacher's Tip: Pure water is a poor conductor, but the water on your hands is always "dirty" enough to conduct well.
Exam Tip: Connect "wet hands" to "shock risk" in your safety explanations.

B. Short/Long Answer Questions

Question 1: State two properties of a bar magnet.
Answer:
Properties of a bar magnet
1. Attractive property : A magnet attracts small pieces of iron, cobalt or nickel.
2. Directive property : A magnet when suspended freely, always point towards North and South direction.
3. Like poles i.e. North and North or South and South poles repel each other.
4. Unlike poles i.e. North and South attract each other.
5. Poles always exist in pairs, i.e. poles of a magnet cannot be separated.
Magnets are unique because they have concentrated areas of force at their ends called poles. These properties allow us to use magnets for everything from holding notes on a fridge to navigating ships at sea.
Teacher's Tip: Use "North-South" for direction and "Opposites Attract" for poles.
Exam Tip: List the "Directive Property" as it's the foundation for the magnetic compass.

Question 2: How will you test whether a given rod is a magnet or not ?
Answer:
Aim - To test whether a given rod is a magnet or not.
Apparatus - 1. rod to be tested, 2. a bar magnet, 3. a stand, 4. a thread.
Procedure -
1. Suspend the rod to be tested with a thread on the stand.
2. Bring the bar magnet near the rod with its north pole towards the rod’s end.
3. Observe.
Inference - In every case, the magnet comes to rest in a north- south direction which shows its directive property.
Observation and Inference -
- If the rod is attracted towards the bar magnet, the rod may be magnet or not.
- But if the rod remains in the same direction of rest as in the start of the experiment, it show it is not a magnet.
A simple attraction test isn't enough because a magnet will attract any iron rod, even if the rod itself isn't magnetic. The true test of a magnet is its ability to point North-South or to repel another magnet's same pole.
Teacher's Tip: Repulsion is the "sure test" of magnetism.
Exam Tip: Describe the suspension of the rod as the key step for testing the directive property.

Question 3: How will you test whether a given rod is made of iron or not?
Answer: Bring a magnet near the rod if the rod is attracted by the magnet then it will be made of iron else not.
Iron is a ferromagnetic material, meaning it is strongly pulled toward any magnetic field. If the rod doesn't move toward the magnet at all, it's likely made of a non-magnetic material like wood or plastic.
Teacher's Tip: This test identifies "magnetic substances," not necessarily magnets themselves.
Exam Tip: Note that metals like copper and aluminum will *not* be attracted, so they are not iron.

Question 4: You are given two similar bars. One is a magnet and the other is of soft iron. How will you distinguish and identify them ?
Answer: Take first bar and suspend it in a stand with the help of a thread. So that it is free to rotate in horizontal plane. Note the direction in which it sets itself. If the direction is North and South it may be magnet. Again rotate it, if this time again it sets itself in north and south direction, it is a magnet, otherwise it is iron. Now repeat above experiment with second bar and in the same way find it if it sets always in north and south direction then it will be a magnet.
The bar that always aligns with the Earth's poles is the magnet because it has its own permanent magnetic field. The iron bar will simply rest in whatever direction you leave it because it lacks that internal directive force.
Teacher's Tip: Only a magnet has a "favorite" direction to point in.
Exam Tip: Use the word "suspension" to describe hanging the bar so it can spin freely.

Question 5: You are given a magnet. How will you use it to find north- south direction at a place ?
Answer: The earth is a huge magnet in itself with its North and South poles. The North and South of the place can easily be detected with the help of a bar magnet. A freely suspended bar magnet always rest in the geographic N-S direction. Since the South pole of the earth’s magnet is closer to the geographic North, the North pole of the suspended magnet will always rest in the geographic North, and the South pole of the freely suspended magnet will point towards geographic South.
By hanging the magnet by a thread, you allow it to act as a compass needle that interacts with the planet's magnetic field. This is how sailors found their way across oceans before modern GPS existed.
Teacher's Tip: The magnet's "North pole" is actually attracted to the Earth's "Magnetic South" (which is near the geographic North).
Exam Tip: State that the magnet must be "freely suspended" for this method to work.

Question 6: Describe a simple experiment to illustrate that like poles of two magnets repel each other while the unlike poles attract.
Answer: Like poles repel and unlike poles attract. Two like poles (both North poles or both South poles) repel each other. Two unlike poles (one North pole and the other South pole) attract each other. This can be demonstrated by the following simple experiment.
Take two bar magnets A and B. Suspend one magnet A with a silk thread from a support so that it is free to swing. The magnet A will come to rest in the North-South direction. The North pole of the magnet A is in the North direction and its South pole is in the South direction. Now holding the other magnet B in your hand if you bring its North pole near the North pole of the suspended magnet A as shown in figure you will observe that the two poles repel each other. Care is taken that the two magnets do not touch each other. Now if you bring the South pole of the magnet B near the north pole of the suspended magnet A as shown in figure without touching it, you will observe that the two poles attract each other.
The experiment shows that magnets exert a force on each other through space without needing to touch. This push or pull depends entirely on which ends are facing each other.
Teacher's Tip: Use two same-colored ends to test repulsion and different-colored ends to test attraction.
Exam Tip: Draw two diagrams: one showing N-N (arrows pointing away) and one showing N-S (arrows pointing together).

Question 7: “Poles exist in pair”. Comment on this statement.
Answer: The magnetic poles always exist in pairs. It is not possible to separate the two poles of a magnet.
If a bar magnet is broken at the middle in two parts each part is found to be a magnet. Each part has the property to attract the small iron pieces. Each part rests in the North South direction when suspended such as to swing freely. This shows that the new poles are formed at the broken ends.
If these pieces are broken again and again, each part will still found to be a complete magnet. Each part contains both the poles (N-pole and S-pole). Thus, the two poles of a magnet exist simultaneously.
Magnetism is an atomic property, so you can never cut a magnet small enough to have just a "North" piece. Even at the microscopic level, every tiny fragment will still have two opposite ends.
Teacher's Tip: Magnet poles are like "heads and tails" on a coin; you can't have a coin with only one side!
Exam Tip: Use the term "magnetic dipole" to describe the permanent pairing of North and South.

Question 8: What is a magnetic compass ? State its use.
Answer: Magnetic compass is a device which is used to locate the direction of a place. It always rests in a North-South direction. It is used in the navigators in - ships, submarines, aeroplanes etc.
It consists of a tiny, lightweight needle magnet balanced on a pivot inside a protective case. The needle spins freely until its North pole points toward the Earth's magnetic North.
Teacher's Tip: The "N" on the compass stands for North, which helps you find all other directions.
Exam Tip: Identify "navigation" as the primary real-world use for a magnetic compass.

Question 9: Explain the meaning of the term magnetic field.
Answer: The space around the magnet where its influence can be experienced is known as magnetic field. This field is formed by the magnetic lines of force which run from the North pole to the South pole. These lines can be found to be maximum crowded at the two ends of the magnet which are the poles i.e. the North pole and the South pole.
Imagine an invisible zone of power surrounding the magnet that can pull on nearby iron objects. The closer you are to the magnet's ends, the stronger this invisible "grip" or field becomes.
Teacher's Tip: Sprinkle iron filings around a magnet to see the field "lines" appear before your eyes!
Exam Tip: Mention that the field is "strongest at the poles" for full marks.

Question 10: What is an electromagnet ?
Answer: An electromagnet - An electromagnet is a temporary magnet which behaves as a magnet when electric current is passed through the insulated copper wire and loses its magnetism when current is stopped. It has a soft iron piece called the core with an insulated copper wire wound on it.
It is essentially a "controllable magnet" that we can turn on or off with a switch. This makes it incredibly useful for picking up cars in scrap yards or making bells ring.
Teacher's Tip: Electromagnet = Electricity + Magnet.
Exam Tip: Emphasize that it is a "temporary" magnet in your definition.

Question 11: Name the material of an electromagnet.
Answer: Iron bar, insulated copper wire, battery.
These three components work together: the battery provides power, the wire carries it in loops, and the iron bar concentrates the magnetic force. Insulation on the wire is key so the current flows through the loops and doesn't just short-circuit through the core.
Teacher's Tip: "Insulated" wire is important so the electricity stays in the "lane" of the coils.
Exam Tip: List all three materials if asked for what an electromagnet is "made of."

Question 12: Draw a labelled diagram to make a soft iron bar as an electromagnet. Describe in steps the procedure.
Answer:
Usually, the electromagnets are made in two shapes : (1) bar or I shaped magnet and (2) horse shoe or U shaped magnet.
1. To make a bar or I shaped electromagnet: Take a soft iron bar PQ and wind a thin insulated copper wire around the bar. Connect a cell or a battery B, and a key K in series between the ends of the coil. The circuit diagram is shown in figure. When key K is closed, current passes through the winding of the coil and the bar becomes a magnet. As the key K is opened, the current stops flowing in the coil and the bar loses its magnetism. Thus, the bar behaves like an electromagnet.
2. To make a horse shoe or U shaped electromagnet: Take a U shaped soft iron piece. Wind a thin insulated copper wire on its arms such that the winding in the two arms is in opposite direction. In figure winding in the arm A starts from the front and is in clockwise direction (when seen from the bottom). On reaching the upper end of the arm A, winding starts from the back at the top of the arm B and is in anticlockwise direction. Connect a battery B and a key K between the two ends of the wire.
Creating loops of wire around the iron increases the magnetic field significantly. The battery provides the necessary "push" for the electrons to move through those loops and generate the force.
Teacher's Tip: The more loops you wind, the stronger your magnet will be!
Exam Tip: Label the "Core," "Coils," and "Battery" clearly in your diagram.

Question 13: You are given a U shaped soft iron piece, insulated copper wire and a battery. Draw a circuit diagram to make a horse shoe electromagnet.
Answer: End A becomes S-pole and B becomes N-pole.
In a horseshoe electromagnet, the wire is wound so that one end of the 'U' becomes a North pole and the other becomes a South pole. This concentrates the magnetic force between the two nearby ends, making it very powerful.
Teacher's Tip: The "U" shape brings both poles to the same side, making it much easier to pick up flat objects.
Exam Tip: Draw the wire coils wrapping around both sides of the "U" for a correct diagram.

Question 14: Name two factors on which the strength of magnetic field of an electromagnet depends.
Answer: The magnetic field of an electromagnet (I or U-shaped) can be increased by the following two ways :
1. By increasing the number of turns of winding in the solenoid.
2. By increasing the current through the solenoid.
More loops of wire mean more magnetic "power" added together, and a stronger battery means more electrons are flowing to create that power. Adjusting these two things allows engineers to build electromagnets of any strength.
Teacher's Tip: Think of it like this: More wire = More power; More battery = More power.
Exam Tip: Use the term "number of turns" specifically when referring to the wire coils.

Question 15: State two ways by which the strength of magnetic field of an electromagnet can be increased.
Answer: The magnetic field of the electromagnet can be increase in the following two ways :
1. By inserting a rod of soft iron or steel inside the cylindrical tube. This rod is called the core.
2. By increasing the total number of turns of the coil.
Adding an iron core is like putting a megaphone on a quiet voice; it helps project the magnetism much further and stronger. Increasing the number of turns simply adds more layers of magnetic force together.
Teacher's Tip: Core + Coils = Super Magnet!
Exam Tip: Mention "Soft Iron" specifically as the core for increasing strength temporary magnets.

Question 16: State two common uses of electromagnets.
Answer: Uses of electromagnet -
1. In electrical appliances such as electric bell, fan etc.
2. In lifting heavy loads of iron scrap.
3. To remove tiny particles of iron from the wound.
4. In loading furnaces with iron.
5. In separation of magnetic substances from the non-magnetic substances.
Electromagnets are vital in industry for heavy lifting and sorting metals. In medicine, specialized electromagnets help doctors safely remove metal splinters from a patient's body or eyes.
Teacher's Tip: Think of the big magnets on cranes in cartoons—those are electromagnets!
Exam Tip: List "Electric Bell" and "Lifting iron scrap" as your primary examples.

Question 17: Name a domestic device in which an electromagnet is used.
Answer: Electromagnet is used in ELECTRICAL APPLIANCES like ELECTRIC BELL, RADIO, T.V., FAN and MOTORS etc.
Inside your home, the electric fan uses electromagnets to push against permanent magnets and create the spinning motion. The electric bell uses them to vibrate the hammer and create the ringing sound you hear.
Teacher's Tip: If it has a speaker (like a TV or Radio), it definitely has an electromagnet!
Exam Tip: "Electric Bell" is the safest answer to give for a domestic device question.

Question 18: Draw a neat and labelled diagram of an electric bell and describe its working.
Answer: Working of the bell - Principle of working of electromagnetism When the switch is pushed on, the circuit gets completed and current stalls flowing through the U-shaped electromagnet which creates magnetic field in the core. This attracts the iron armature. Now when the armature moves towards the electro-magnet, the hammer strikes the gong and the bell rings. But as the armature moves towards the electromagnet, the contact with the adjustment screw breaks which breaks the closed circuit and stops the current. Now when there is no current there is no electromagnetism and the armature returns to the original position. This making and breaking of the circuit of the electromagnet continues as long as the button remains pressed.
The bell is a perfect example of a "self-interrupting" circuit that creates rapid movement. This cycle happens many times every second, causing the hammer to hit the gong so fast it sounds like a continuous ring.
Teacher's Tip: The switch in the bell is like a person constantly turning a light on and off very fast.
Exam Tip: Describe the "make and break" of the circuit clearly to explain the ringing action.

Question 19: The incomplete diagram of an electric bell is given in fig. Complete the diagram and label its different parts.
Answer: (As per the completed diagram in the textbook showing: Hammer, Gong, Adjusting screw, Armature, Electromagnet, Battery, Switch).
The diagram must show a battery connected through a switch to the electromagnet coils. One end of the circuit must go through the screw and armature so that the movement of the armature can break the connection.
Teacher's Tip: Make sure the wire from the battery passes through the contact screw to the hammer.
Exam Tip: Label the "Gong" and "Hammer" specifically, as they are the parts that produce the sound.

Question 20: What is declination ? Draw a diagram to show the angle between the declination and true direction of geographic north.
Answer: Magnetic declination is the angle of the horizontal plane between the magnetic North and the geographic North (or true North). This angle is shown in figure by symbol theta. The angle of declination is different at different places on the earth surface and it also changes at a place with time. The declination is taken positive if the magnetic North is towards the east of the true North as in figure and is negative if the magnetic north if towards the west of the true North.
Because the Earth's magnetic core isn't perfectly lined up with its axis of rotation, a compass doesn't point to the exact "top" of the world. Navigators use maps of declination to adjust their compasses so they don't get lost.
Teacher's Tip: Declination is just the "error" or gap between the real North and the magnetic North.
Exam Tip: Draw two arrows starting from one point, one labeled "Geographic North" and one "Magnetic North," with the angle theta between them.

Question 21: Define the term current.
Answer: An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. The S.I. unit of electric current is the ampere.
Think of current like water flowing through a pipe; the more "water" (charge) that passes a point each second, the higher the current. The Ampere (A) is the standard measurement for how much electricity is zipping through a wire.
Teacher's Tip: Current is "charge in motion."
Exam Tip: Always mention the S.I. unit "Ampere" when defining current for full marks.

Question 22: Name four appliances which work using electricity.
Answer: 1. an electric iron, 2. an electric heater, 3. an electric kettle, 4. an immersion rod.
These appliances all convert electrical energy into thermal energy to perform tasks like ironing clothes or boiling water. They demonstrate the "heating effect" of electric current in our everyday lives.
Teacher's Tip: Almost anything with the word "Electric" in its name works this way!
Exam Tip: Providing household examples like a "Toaster" or "Fan" is also correct.

Question 23: Name two sources of electricity.
Answer: 1. dry cell and battery, 2. generator and solar cell.
Chemical sources like dry cells are great for portable power, while mechanical sources like generators provide energy for entire cities. Solar cells are becoming more popular because they turn sunlight directly into electricity.
Teacher's Tip: A source is any device that provides the "push" needed for current to flow.
Exam Tip: List "Solar cell" as a modern source to show updated knowledge.

Question 24: What is a battery ?
Answer: If we use a group of two or more cells, it is called a battery. A battery is used where we require more electricity.
Connecting cells in a row (series) adds their power together to run bigger devices like remote-controlled cars or powerful torches. One single cell is often not strong enough to do the work alone.
Teacher's Tip: 1 cell + 1 cell = 1 Battery.
Exam Tip: Define a battery as a "combination of cells" for a precise scientific answer.

Question 25: What is an electric circuit ?
Answer: For a smooth flow of electric current, a complete circuit is needed. This is known as electric circuit.
A circuit is the entire "loop" that starts at the power source, goes through the appliance, and returns to the source. It must be made of conducting materials and have no gaps for the electricity to flow properly.
Teacher's Tip: No Loop = No Flow. It's a circle of power!
Exam Tip: Mention that a circuit must be "closed" for current to flow.

Question 26: Describe an experiment to show that electricity flows only if the circuit is complete and it does not flow if the circuit is incomplete.
Answer: Take two torch bulbs A and B. Connect them to a cell through a switch as shown in fig. The bulbs are said to be in series. Close the switch (i.e., the circuit it completed), you will see that both the bulbs glow. Now take out the connection of the bulb B as shown in fig. Now close the switch, you will observe that the bulb A does not glow, because the circuit is now incomplete. Now replace the bulb B by a fused bulb fig. and close the switch. Again you will see that the bulb A does not glow. This is because the circuit being in series, is still incomplete.
This experiment proves that electricity requires a continuous "bridge" to travel from one side of the battery to the other. If you remove a bulb or use a broken one, you create a gap that the electrons cannot cross.
Teacher's Tip: This is why if one bulb in a series of Christmas lights breaks, they all go dark!
Exam Tip: Use the terms "Closed Circuit" for complete and "Open Circuit" for incomplete paths.

Question 27: You are provided with a torch bulb, a cell and two plastic coated metal wires. Draw a diagram to show a complete circuit to light the bulb.
Answer: (As per the diagram showing bulbs connected in parallel with switches). Take two bulbs A and B. Connect them through switches S₁ and S₂ in parallel as shown in fig. Close both the switches. You will see that both the bulbs glow.
By connecting the bulb to both terminals of the cell, you create a one-way street for electricity to travel through the light. The plastic coating on the wires ensures the electricity stays inside the wire and doesn't leak out.
Teacher's Tip: Make sure your drawing shows wires touching both the "tip" and the "side" of the bulb base.
Exam Tip: Clearly label the "+" and "-" terminals of the cell in your circuit diagram.

Question 28: In which of the following case the bulb will glow :
1. Only one terminal of a cell is joined with a metal wire to one terminal of the bulb.
2. Both terminals of the bulb are joined with two metal wires to one terminal of the cell.
3. One terminal of the cell is joined to one terminal of the bulb and other terminal of the cell to the other terminal of the bulb.
Answer: The bulb will glow in (3) case.
Only case 3 provides a full loop where current can leave the positive terminal, pass through the bulb, and return to the negative terminal. The other cases leave the circuit "open" or "shorted," so no power reaches the light.
Teacher's Tip: Electricity is like a "return trip" — it always needs to get back to where it started.
Exam Tip: Identify that case 3 represents a "Closed Circuit" while the others do not.

Question 29: Distinguish between conductors and insulators of electricity. Give two examples of each.
Answer:
Conductors
1. Conductors are those substances which allow electricity to flow through them.
2. e.g. all metals, human body.
Insulators
Insulators are those which do not allow electricity to pass through them.
e.g. wood, paper, glass.
Conductors are materials that let energy pass easily, like a door that is wide open. Insulators are like a locked wall that keeps electricity trapped, which is why we use them for safety on handles and wire coatings.
Teacher's Tip: Use "Conductor" for "Current" and "Insulator" for "Inhibition."
Exam Tip: Name specific metals like "Copper" and specific insulators like "Rubber" as your examples.

Question 30: Select conductors and insulators from the following : Glass, silver, copper, wood, paper, pure water, impure water, aluminium, iron, leather, plastic, steel, human body and ebonite.
Answer:
Conductors - Silver, copper, impure water, aluminium, iron, steel, human body.
Insulators - Glass, wood, paper, pure water, leather, plastic and ebonite.
Metals and water with salts (impure) are great at carrying charges. Materials like plastic, glass, and very pure water don't have the free charges needed to allow current to move.
Teacher's Tip: Pure water is an insulator, but tap water is always a conductor because it's "impure"!
Exam Tip: Group your answer into two distinct columns for clarity.

Question 31: The following diagram shows four circuits A, B, C and D. Each circuit has a cell and a torch bulb. Name the circuits in which the bulb will glow ? Give reason to your answer.
Answer: The bulb will glow in circuit (D). This is because copper is the best conductor of electricity as compared to aluminium. Silk is a non-conductor of electricity.
In circuit D, both wires are made of copper, which is a highly efficient conductor. If one wire is made of silk (circuit C) or if the path is broken, the electricity cannot finish its loop and the bulb stays dark.
Teacher's Tip: Silk is a type of cloth, and cloth is always an insulator.
Exam Tip: In "Which circuit will glow" questions, look for the one with no gaps and only metal wires.

Question 32: The diagram given below shows a bulb connected with a cell having terminals A and B. Mark the direction of current in the bulb.
Answer: Current always flows from +ve terminal to the -ve terminal of a cell.
On a diagram, you draw arrows starting from the longer vertical line (positive) of the cell symbol. The arrows should follow the wire through the bulb and point back to the shorter, thicker line (negative) of the cell.
Teacher's Tip: Just remember: High (+) to Low (-).
Exam Tip: Use a ruler to draw neat arrows on the circuit lines to show the flow.

Question 33: State the function of each of the following in an electric circuit and draw its symbolic representation: (1) Switch and (2) Cell.
Answer:
1. Switch – A switch or key is used to put the circuit on and off. fig. shows the symbol of a switch or key when it is open (to put the circuit off) and when it is closed (to put the circuit on). (Symbols show two circles with a line up for open and down for closed).
2. Cell – A cell or a group of cells is generally used as a source of electricity. A positive (+) and a negative (-). It is represented by the two vertical lines of unequal lengths. The long vertical line represents the positive terminal and the short line represents the negative terminal as shown in fig.
The cell provides the electrical energy source, and the switch acts as the controller. Symbols allow scientists to draw complicated circuits quickly using simple, universal shapes.
Teacher's Tip: The long line of the cell is always the "Plus" side.
Exam Tip: Practice drawing the symbols accurately; a cell must have one long and one short line.

Question 34: Draw a circuit diagram for a bulb connected to a cell with a switch. Mark arrow in the diagram to indicate the direction of flow of current.
Answer: (As per the diagram showing a cell connected to a bulb through wires and a switch labeled "Wire," "Bulb," and "Switch").
This diagram shows the complete journey of electricity. Current starts at the positive terminal of the cell, travels through the wire to the bulb, passes through the closed switch, and returns to the negative terminal.
Teacher's Tip: Every circuit diagram needs three things: a Source, a Path, and a Load.
Exam Tip: Don't forget to include the arrows for current direction; many students lose marks for omitting them.

Question 35: In which arrangement are the appliances connected in the electric circuit of our homes, Series or Parallel ? Give one reason for your answer.
Answer: Parallel circuit: When the circuit is in parallel, the appliances work independently. This is the reason that in our household wiring system, all the circuits are in parallel. Every appliance when put on, works on its own without the interruption of the other appliance.
In a parallel circuit, each light or fan has its own direct path to the power source. This means you can turn off your bedroom light without the television in the living room turning off too.
Teacher's Tip: Parallel = Privacy for each appliance's power.
Exam Tip: Mention that in parallel circuits, if one device "fuses" or breaks, the rest stay working.

Question 36: State two precautions that you must take when switching on an electric circuit.
Answer: Precautions to be taken before the circuit is switched on. Before the circuit is switched on, following precautions must be taken :
1. See that all the components of the circuit are properly connected.
2. See that the connection wire is tightly connected to each appliance or component.
3. Do not touch the switch or any component with wet hands.
Proper connections prevent "short circuits" which can cause sparks or fires. Keeping your hands dry ensures that you don't become part of the circuit yourself, which would result in a dangerous shock.
Teacher's Tip: Always "Double-Check before you Flip the Switch"!
Exam Tip: Mention "wet hands" as it is the most critical safety rule for home electricity.