CBSE Class 10 Physics Electricity Worksheet Set D

Multiple Choice Questions

Question. A cylindrical conductor of length ‘l’. and uniform area of cross-section ‘A’ has resistance ‘R’. The area of cross-section of another conductor of same material and same resistance but of length ‘2l’ is
(a) \( \frac{A}{2} \)
(b) \( \frac{3A}{2} \)
(c) 2A
(d) 3A
Answer: (c)

Question. The maximum resistance which can be made using four resistors each of resistance \( \frac{1}{2} \Omega \) is :
(a) 2 Ω
(b) 1 Ω
(c) 2.5 Ω
(d) 8 Ω
Answer: (a)

Question. A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is \( R_2 \), then the ratio \( R/R_2 \) is :
(a) \( \frac{1}{25} \)
(b) \( \frac{1}{5} \)
(c) 5
(d) 25
Answer: (d)

Question. Which of the following terms does not represent electrical power in a circuit ?
(a) \( I^2R \)
(b) \( IR^2 \)
(c) VI
(d) \( V^2/R \)
Answer: (b)

Question. An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be :
(a) 100 W
(b) 75 W
(c) 50 W
(d) 25 W
Answer: (d)

Question. Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be :
(a) 1 : 2
(b) 2 : 1
(c) 1 : 4
(d) 4 : 1
Answer: (c)

Question. Which of the following obeys Ohm’s law ?
(a) Filament of a bulb
(b) LED
(c) Nichrome
(d) Transistor
Answer: (c)

Question. Electrical resistivity of an alloy of copper and nickel is ________ when compared with the electrical resistivity of an alloy of copper, manganese and nickel.
(a) Same
(b) Double
(c) More
(d) Less
Answer: (c)

Question. There is a dual of 8 ohm resistance on the aerial. Determine the aerial’s new resistance.
(a) 2 Ω
(b) 4 Ω
(c) 7 Ω
(d) 10 Ω
Answer: (a)

Question. Let us consider the current flowing through a metallic wire if the temperature of the entire system increases. What will happen from the following options ?
(a) Potential difference (V) increases
(b) Resistance (R) decreases
(c) Potential difference (V) decreases
(d) V and R remains the same
Answer: (c)

Match the following

Question. Match the following
Column I
(a) Series connection
(b) Parallel connection
(c) Device connection parallel to resistor
(d) Device connected in series to a resister.
Column II
(i) \( R_{eq} = \frac{R_1R_2}{R_1 + R_2} \)
(ii) Ammeter.
(iii) \( R_{eq} = R_1 + R_2 \)
(iv) Voltmeter
Answer: (a) (iii), (b) (i), (c) (iv), (d) (ii).

Fill in the blanks

Question. Fill in the blanks
(a) The rate at which electrical work is done, known as ............... .
(b) In parallel connection, of electrical appliances, overall resistance of household circuit is ................ .
(c) ............... is the best conductor of electricity.
Answer: (a) Electric power, (b) reduced, (c) Silver metal.

Very Short Answers Type Questions

Question. Why does the cord of an electric oven not glow while its heating element does ?
Answer: The resistance of heating element of an electric oven is very high. As the current flows through the heating element it becomes too hot and glows red. On the other hand chord of an electric oven low resistance hence, it does not become red during the flow of current.

Question. What would you suggest to a student if while performing an experiment he finds that the pointer/needle of the ammeter and voltmeter do not coincide with the zero marks on the scales when circuit is open ? No extra ammeter/voltmeter is available in the laboratory.
Answer: This is called the zero error of the scale of ammeter or voltmeter. If there is a zero error then this error is subtracted from the value that depicts when the circuit is closed otherwise accurate readings will not be recorded.

Question. Name and define the SI unit of current.
Answer: ‘Ampere‘ is the SI unit of current. 1 Ampere current can be defined as a unit charge flowing per second in the circuit. \( 1 \text{ Ampere} = \frac{1 \text{ Coulomb}}{1 \text{ Second}} \).

Question. Write the function of voltmeter in an electric circuit.
Answer: Voltmeter measures the potential difference across two points in a circuit. It is always connected in parallel in the circuit.

Question. The following table gives the value of electrical resistivity of some materials :
1. Copper: \( 1.62 \times 10^{-8} \Omega\text{-m} \)
2. Silver: \( 1.6 \times 10^{-8} \Omega\text{-m} \)
3. Constantan: \( 49 \times 10^{-8} \Omega\text{-m} \)
Which one is the best conductor of electricity out of them ?
Answer: Silver, because its electrical resistivity is least out of the given materials.

Question. Which substance is used for making resistance coil of electric heater and why ?
Answer: Nichrome, due to its high resistivity.

Question. Why is an ammeter connected in series in an electric circuit ?
Answer: It is connected in series so that whole of electric current, which it has to measure, passes through it.

Question. Name the alloy which is used for making the filament of bulbs.
Answer: Tungsten is used for making the filament of bulbs.

Question. Why closed path is required for the flow of current ?
Answer: It makes possible to move the electrons in a particular direction, so closed path is necessary for the flow of current.

Question. State some properties of charge.
Answer: Properties of Charge : (a) Electric charge can neither be created nor be destroyed but it can transfer from one body to another i.e., total electric charge in an isolated system is conserved. (b) Total charge on a body is equal to the algebraic sum of all the charges located on that body.

Question. When two ends of a metallic wire are connected across the terminals of a cell, some potential difference is set up between its ends. In which direction, electrons are flowing through the conductors ?
Answer: From a lower potential end of a metallic conductor to its higher potential end.

Question. Electric current flows through a metallic conductor from its one end A to other end B. Which end of the conductor is at higher potential ? Why ?
Answer: Current always flow from a higher potential to a lower potential end of the conductor. So end ‘A’ of the conductor is at a higher potential.

Question. Define current.
Answer: Current is defined as the rate of flow of charge. If a charge ‘Q’ flows through the cross-section of a conductor in time ‘t’, then the current ‘I’ through it is given as : \( I = \frac{Q}{t} \).

Question. State Ohm’s law.
Answer: According to the Ohm’s law, the current flowing in a conductor is directly proportional to the potential difference applied across its ends, provided the temperature and other physical conditions of the conductor remain constant.

Short Answers Type Questions

Question. (a) Write Joule’s law of heating. (b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V.
Answer: (a) According to Joule’s law of heating, the heat produced in a wire is directly proportional to 1. square of current \( (I^2) \), 2. resistance of wire (R), 3. time (t) for which current is passed. Thus, \( H = I^2Rt \). (b) We know that, \( P = VI \Rightarrow I = \frac{P}{V} \). First lamp : \( I_1 = \frac{100}{220} = 0.45 \text{ A} \). Second lamp : \( I_2 = \frac{60}{220} = 0.27 \text{ A} \). Total current \( I = I_1 + I_2 = 0.45 + 0.27 = 0.72 \text{ A} \).

Question. A torch bulb when cold has a resistance of \( 2.5\ \Omega \). It draws a current \( 450\ \text{mA} \), when connected to a \( 6\ \text{V} \) battery and glows brightly. Calculate the resistance of the bulb when glowing and explain the reason for the difference in resistance.
Answer: While glowing, \( I = 450\ \text{mA} = 0.45\ \text{A} \), \( V = 6\ \text{volt} \)
Using Ohm’s law,
Resistance of bulb, \( R = \frac{V}{I} = \frac{6}{0.45} = 13.33\ \Omega \)
The reason for the difference in resistance of bulb when cold \( (R = 2.5\ \Omega) \) and while glowing \( (R = 13.33\ \Omega) \), is that the resistance of filament of bulb increases with the increase in temperature.

Question. Two lamps, one rated \( 100\ \text{W} \) at \( 220\ \text{V} \), and the other \( 60\ \text{W} \) at \( 220\ \text{V} \), are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is \( 220\ \text{V} \) ?
Answer: Given : Power of one lamp, \( P_1 = 100\ \text{W} \)
Power of second lamp, \( P_2 = 60\ \text{W} \)
Since, both the lamps are connected in parallel, thus, potential difference will be equal.
Thus, potential difference \( = 220\ \text{V} \)
We know that,
Power \( (P) = VI \)
Thus, the total current through the circuit
\( I = \frac{P_1}{V} + \frac{P_2}{V} \)
\( I = \frac{100}{220} + \frac{60}{220} \)
\( = \frac{100 + 60}{220} \)
\( = \frac{160}{220} = 0.727\ \text{A} \)

Question. What is (a) the highest, (b) the lowest total resistance that can be secured by combination of four resistors of \( 1\ \Omega, 10\ \Omega, 100\ \Omega \) and \( 1000\ \Omega \) ?
Answer: (a) To obtain the highest resistance, the resistors must be connected in series.
\(\therefore\) Highest resistance, \( R_s = (1 + 10 + 100 + 1000)\ \Omega = 1111\ \Omega \)
(b) To obtain the lowest resistance, the resistors must be connected in parallel.
The lowest resistance is given by
\( \frac{1}{R_p} = \frac{1}{1} + \frac{1}{10} + \frac{1}{100} + \frac{1}{1000} \)
\( = \frac{1000 + 100 + 10 + 1}{1000} \)
\( = \frac{1111}{1000} \)
\(\therefore\) Lowest resistance, \( R_p = \frac{1000}{1111}\ \Omega \approx 0.9\ \Omega \).

Question. Why is a series arrangement not used for domestic circuits ?
Answer: Series arrangement is not used for domestic circuits for the following reasons :
(a) The voltage of the source gets divided in all the appliances connected in series, in the ratio of their resistances, so each appliance does not operate at its rated voltage.
(b) The resistance of the circuit increases and it reduces the current in the circuit, so each appliance gets less power.
(c) If any one appliance in series arrangement is switched off (or gets spoilt), no other appliance connected with it in series will then operate.

Question. State the energy conversion taking place in the following electric appliances : (a) Electric heater, (b) Electric motor, (c) Loud-speaker, (d) Electrolysis.
Answer: (a) Electrical energy gets converted into heat energy in an electric heater.
(b) Electrical energy changes into mechanical energy in an electric motor.
(c) Electrical energy gets converted into sound energy in a loudspeaker.
(d) Electrical energy changes into chemical energy during electrolysis.

Question. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series ?
Answer: Advantages of connecting electrical appliances in parallel instead of connecting in series :
(a) Voltage remains same in all the appliances.
(b) The total effective resistance is less.
(c) Switching ON/OFF of one device doesn’t affect others.

Question. (a) List the factors on which the resistance of a conductor in the shape of wire depends.
(b) Why are metals good conductors of electricity whereas glass is a bad conductor of electricity ? Give reason.
(c) Why are alloys commonly used in electrical heating devices ? Give reason.
Answer: (a) Resistance of a conductor depends directly on its length and is inversely proportional to the area of cross-section.
(b) Metals have free electrons and they move and conduct electricity, whereas glass does not allow electrons and charges to flow freely as it is an insulator.
(c) The resistivity of an alloy is generally higher than that of its constituent metals. Alloys do not oxidise (burn) readily at higher temperatures. Therefore, conductor of electric heating devices, such as toasters and electron irons are made of an alloy rather than pure metal.

Assertion and Reasoning Based Questions

Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false but reason is true.

Question. Assertion : Alloys are used in making electric irons, toasters etc.
Reason : Because the resistivity of alloys is lower than its constituent metals.
(a) A
(b) B
(c) C
(d) D
Answer: (c)
Answer: For using the alloys in making toasters, electric iron is based on only one reason for resistivity. If the resistivity of the material is high which is being used to make these items, then heat dissipation will be more. And these items are used for heating only. So, the reason is wrong. So, assertion is true, but the reason is false.

Question. Assertion : In a circuit which is having 3 series resistors of \( R \) ohm each, the total resistance of the circuit will be \( 3R \).
Reason : As in parallel circuit the resultant resistance will be \( \frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} \)
(a) A
(b) B
(c) C
(d) D
Answer: (b)
Answer: Resultant resistance is the addition of individual present in the series circuit. So, according to the above statement, Resultant resistance \( (R) = R_1 + R_2 + R_3 \). So total resistance will be \( 3R \). In parallel combination, resultant resistance will be \( \frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} \). Here, both assertion and reason are true and reason is the correct explanation of assertion.

Question. Assertion : An ammeter is always connected in parallel with the circuit for which current has to be measured.
Reason : As the current in a parallel circuit is not same.
(a) A
(b) B
(c) C
(d) D
Answer: (d)
Answer: In a series circuit always the current measured will be same, this is the reason why ammeter is always connected in series with the circuit for which the measurement has to be done. Thus, assertion is false but reason is true.

Question. Assertion : When more current flows to an electrical equipment it shows more heating of the same.
Reason : Heat flow is directly proportional to the square of current only.
(a) A
(b) B
(c) C
(d) D
Answer: (c)
Answer: Assertion is true but the reason is false. As heat flow is dependent on three factors : (i) Current flowing through it (ii) Time period of flow of current (iii) Resistance of the conductor. So, the reason is false that heat flow only depends on square of current. As it is dependent on several other factors too.

Question. Assertion : Bulbs are filled with inactive nitrogen and argon gases.
Reason : As there is a requirement of thermal isolation of the filament.
(a) A
(b) B
(c) C
(d) D
Answer: (a)
Answer: Most of the part of consumed power of bulb is dissipated as heat but very less part gets converted into light. So, there is a need for thermal isolation in order to reduce heat losses. This is the reason why bulbs are filled with inactive nitrogen and argon. So, both assertion and reason is true and reason is the correct explanation of assertion.

Creating Based Questions

Question. Brisilia designed a prototype in which she used a very sensitive electrical device. But she does not know how to protect the sensitive electrical device from high current. Suggest her with one idea to protect the sensitive device from high current.
Answer: The suggestion to protect the sensitive electrical device from high current by using a parallel low resistor known as shunt resistor. The resistance value of shunt resistor is very low. It is made up of the material having low temperature coefficient of resistance. It measures the electric current, alternating current or direct current.

Question. Rita designed a circuit in which is resistor are connected in series. Yet she is not satisfied with the series resistors because if there is a fault in some component of the circuit, then whole circuit stop working. What would be your suggestion in alternative to the resistance in series ?
Answer: To overcome the problem faced by Rita, I would suggest to connect the resistor in parallel because if the resistors are connected parallel, the whole circuit does not stop working. If the fault is with one component of the circuit, the current continues to flow through the other components of the circuit which makes the device work further.

Question. What would be your explanation for your friend who thinks that electrons are consumed in an electric circuit ?
Answer: The electrons are not consumed in an electric circuit. The energy provided by the electricity company is used to move electrons through electric gadgets like an electric bulb, fan and engines. We pay to electricity board for providing the energy.

Question. Ashwini suggested an idea that Tungsten can be used for electricity transmission. How can you explain to her that it is not the best proposal and what would be your suggestion for electricity transmission ?
Answer: Tungsten is used for making filaments since it has very high melting point. It is very bad power transmission since most of the energy is lost in the form of heat and light. The best suggestion for electricity transmission is the usage of copper and aluminium wires which are good conductors of electricity and it has high electron mobility.

Question. Using the following information form a pathway to explain the flow of charges inside wire. And also include information that is not mentioned below to complete it. Electrons, solid conductor, solid crystal, drift speed, steady current
Answer: In solid the atoms are very tightly packed → with little space which makes the electrons to travel → smoothly in the solid crystal similar to → a vacuum. The electrons motion in a solid conductor is → different from the empty space charges. The electrons move with average drift speed → when the steady current flows through the conductor.

Paragraph/Table and Case Study Based Questions

In series circuits the energy from the supply is shared between the devices in the circuit. The more are devices added in series, the lower is the potential difference across each one. Hence the less energy is received by each one.

Question. Three resistors each of \( 2\Omega \) are connected together in a triangular shape. The resistance between any two vertices will be:
(a) \( 4/3\Omega \)
(b) \( 3/4\Omega \)
(c) \( 3\Omega \)
(d) \( 6\Omega \)
Answer: (a)

Question. Which arrangement of four identical resistances should be used to draw maximum energy from a cell of voltage \( V \).
(a) Image A (Series)
(b) Image B (Parallel)
(c) Image C (Mixed)
(d) Image D (Mixed)
Answer: (b)

Question. One kilowatt hour is equal to:
(a) \( 36 \times 10^5 \) joules
(b) \( 36 \times 10^3 \) joules
(c) \( 10^3 \) joules
(d) \( 10^5 \) joules
Answer: (a)

Question. Two electric bulbs whose resistances are in the ratio of 1:2 are connected in parallel to a constant voltage source. The powers dissipated in them have the ratio.
(a) 1:2
(b) 1:1
(c) 2:1
(d) 1:4
Answer: (c)

Question. Two heater wires of equal length are first connected in series and then in parallel. The ratio of heat produced in the two cases is:
(a) 2:1
(b) 1:2
(c) 4:1
(d) 1:4
Answer: (d)

The following apparatus is available in a laboratory which in summarised in tabular form :

• S.No 1. Battery adjustable from of to 4.5 V. Resistors: \( 3\Omega \) and \( 6\Omega \)
• S.No 2. Ammeters: \( A_1 \) of range 0 to 3 A (least count 0.1 A); \( A_2 \) of range 0 to 1 A (least count 0.05 A).
• S.No 3. Voltmeters: \( V_1 \) of range 0 to 10 V (least count 0.5 V); \( V_2 \) of range 0 to 5 V (least count 0.1 V).

Question. For what purpose an ammeter is used ?
Answer: To measure current in the circuit.

Question. If we require the maximum resistance from a number of given resistors we connect :
(i) all in series
(ii) all in parallel
(iii) less resisters in series and lens in parallel
Answer: (i)

Question. The best combination of voltmeter and ammeter for finding the equivalent resistance of the resistors in series would be :
(i) ammeter \( A_1 \) and voltmeter \( V_1 \)
(ii) ammeter \( A_1 \) and voltmeter \( V_2 \)
(iii) ammeter \( A_2 \) and voltmeter \( V_1 \)
(iv) ammeter \( A_2 \) and voltmeter \( V_2 \)
Answer: (iv)

Question. For the experiment to find the equivalent resistance of the parallel combination of the two given reasistors, the best choice would be :
(i) ammeter \( A_1 \) and voltmeter \( V_1 \)
(ii) ammeter \( A_1 \) and voltmeter \( V_2 \)
(iii) ammeter \( A_2 \) and voltmeter \( V_1 \)
(iv) ammeter \( A_2 \) and voltmeter \( V_2 \)
Answer: (iii)

Archives

Question. Explain the use of an electric fuse. What type of material is used for fuse wire and why ?
Answer: An electric fuse is used as a safety device in electrical circuits to prevent damage due to excessive current. It consists of a piece of wire made of a material having a low melting point (e.g., an alloy of lead and tin). When current exceeds a safe limit, the wire melts and breaks the circuit.

Question. You have three resistors of \( R\ \Omega \) each and a battery of \( E \) volts. How would you connect these resistors with the battery to obtain maximum current ? Draw a circuit diagram to illustrate your answer and also calculate the current drawn from the battery.
Answer: To obtain maximum current, the resistors must be connected in parallel so that the total resistance is minimum. The effective resistance \( R_p \) for three identical resistors in parallel is \( R/3 \). The current drawn from the battery is \( I = E / (R/3) = 3E/R \).

Question. (a) Write two points of difference between electric energy and electric power.
(b) Out of 60 W and 40 W lamps, which one has a higher electrical resistance when in use.
(c) What is commercial unit of electric energy ? Convert it into Joules
Answer: (a) Electric energy is the total work done by electric current in a given time, while electric power is the rate at which electrical energy is consumed. Unit of energy is Joule (J), unit of power is Watt (W).
(b) Resistance \( R = V^2/P \). Since voltage is constant, resistance is inversely proportional to power. Therefore, the 40 W lamp has a higher electrical resistance.
(c) The commercial unit of electric energy is the kilowatt-hour (kWh). \( 1\ \text{kWh} = 1000\ \text{W} \times 3600\ \text{s} = 3.6 \times 10^6\ \text{J} \).