CBSE Class 10 Physics Electricity Worksheet Set C

Question. If the current I through a resistor is increased by 100% (assume that temperature remains unchanged), the increase in power dissipated will be
(A) 100%
(B) 200%
(C) 300%
(D) 400% 

Answer : C

Question. When a 4 V battery is connected across an unknown resistor there is a current of 100 mA in the circuit. The value of the resistance of the resistor is:
(A) 4 Ω
(B) 40 Ω
(C) 400 Ω
(D) 0.4 Ω 

Answer : B

Question. Two bulbs of 100 W and 40 W are connected in series. The current through the 100 W bulb is 1 A. The current through the 40 W bulb will be:
(A) 0.4 A
(B) 0.6 A
(C) 0.8 A
(D) 1 A 

Answer : D

Question. Unit of electric power may also be expressed as:
(A) Volt-ampere
(B) Kilowatt-hour
(C) Watt-second
(D) Joule-second 

Answer : A

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) A/2
(B) 3A/2
(C) 2 A
(D) 3 A

Answer : C

Question. The resistivity does not change if :
(A) the material is changed.
(B) the temperature is changed.
(C) the shape of the resistor is changed.
(D) both material and temperature are changed. 

Answer : C

Question. A cell, a resistor, a key, and ammeter are arranged as shown in the circuit diagrams given below. The current recorded in the ammeter will be:

(A) Maximum in (i).
(B) Maximum in (ii).
(C) Maximum in (iii).
(D) The same in all the cases. 

Answer : D

Question. In an electrical circuit three incandescent bulbs A, B, and C of rating 40 W, 60 W, and 100 W, respectively are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness?
(A) Brightness of all the bulbs will be the same.
(B) Brightness of bulb A will be the maximum.
(C) Brightness of bulb B will be more than that of A.
(D) Brightness of bulb C will be less than that of B.

Answer : C

Question. The maximum resistance which can be made using four resistor each of resistance 1/2 Ω is
(A) 2 Ω
(B) 1 Ω
(C) 2.5 Ω
(D) 8 Ω

Answer : A

Question. An electric kettle consumes 1 kW of electric power when operated at 220 V. A fuse wire of what rating must be used for it?
(A) 1 A
(B) 2 A
(C) 4 A
(D) 5 A 

Answer : D

Question. What is the maximum resistance which can be made using five resistors each of 1/5 Ω?
(A) 1/5 Ω
(B) 10 Ω
(C) 5 Ω
(D) 1 Ω 

Answer : D

Question. Electrical resistivity of a given metallic wire depends upon 
(A) its length.
(B) its thickness.
(C) its shape.
(D) nature of the material.

Answer : D

Question. What is the minimum resistance which can be made using five resistors each of 1/5 Ω?
(A) 1/5 Ω
(B) 1/25 Ω
(C) 1/10 Ω
(D) 25 Ω 

Answer : B

Assertion and Reason Based MCQs :

Directions : In the following questions, A statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as.
(A) Both A and R are true and R is the correct explanation of A.
(B) Both A and R are true but R is NOT the correct explanation of A.
(C) A is true but R is false.
(D) A is false and R is true.

Question. Assertion (A): Two resistance having value R each. Their equivalent resistance is R/2 .
Reason (R): Resistances are connected in parallel.

Answer : A

Question. Assertion (A): Copper is used to make electric wires.
Reason (R): Copper has very low electrical resistance.

Answer : A

Question. Assertion (A): The resistivity of conductor increases with the increasing of temperature.
Reason (R): The resistivity is the reciprocal of the conductivity.

Answer : B

Question. Assertion (A): Electric appliances with metallic body have three connections, whereas an electric bulb has a two pin connection.
Reason (R): Three pin connections reduce heating of connecting wires.

Answer : C

Question. Assertion (A): Bending a wire does not affect electrical resistance.
Reason (R): Resistance of wire is proportional to resistivity of material.

Answer : A

Question. Assertion (A): Silver is not used to make electric wires.
Reason (R): Silver is a bad conductor of electricity.

Answer : C

Question. Assertion (A): Alloys are commonly used in electrical heating devices like electric iron and heater.
Reason (R): Resistivity of an alloy is generally higher than that of its constituent metals but the alloys have low melting points than their constituent metals.

Answer : C

Case-based MCQs :

Read the passage and answer the questions given below :

Three resistors of 5 Ω, 10 Ω and 15 Ω are connected in series and the combination is connected to the battery of 30 V. Ammeter and voltmeter are connected in the circuit.

Question. Two students perform experiments on two given resistors R₁ and R₂ and plot the following V-I graphs. If R₁> R₂, which of the diagrams correctly represent the situation on the plotted curves? 

Answer : C

Question. Which of the following is connected in series in circuit?
(A) Ammeter
(B) Voltmeter
(C) Both of these
(D) None of these 

Answer : A

Question. Which of the following is the correct circuit diagram to connect all the devices in proper correct order.

Answer : D

Question. How much is the total resistance in the above circuit diagram?
(A) 30 Ω
(B) 20 Ω
(C) 11/30 Ω
(D) 30/11 Ω

Answer : A

Study the given table and answer the questions given below :

Question. Element used to make filament of incandescent bulb is:
(A) Copper
(B) Silver
(C) Nichrome
(D) Tungsten 

Answer : D

Question. What happens to resistance of a conductor when its area of cross section is increased?
(A) Resistance increases
(B) Resistance decreases
(C) No change
(C) Resistance doubles 

Answer : B

Question. Which is a better conductor ?
(A) Chromium
(B) Nickel
(C) Mercury
(D) Iron 

Answer : B

Question. Element used to make heating element of electric geyser is :
(A) Iron
(B) Silver
(C) Nichrome
(D) Tungsten 

Answer : C

IV. Electrical resistivities of some substances, at 20°C are given below in the table. Study the table and answer the given questions.

Question. Series arrangement is not used for domestic circuits because:
(A) Current drawn is less
(B) Current drawn is more
(C) Neither of the above
(D) Both of the above 

Answer : A

Question. Which element will be used for electrical transmission lines ?
(A) Iron
(B) Copper
(C) Tungsten
(D) mercury 

Answer : B

Question. Which is a better conductor of electric current ?
(A) Silver
(B) Copper
(C) Tungsten
(D) Mercury 

Answer : A

Question. Nichrome is used in the heating elements of electric heating device because:
(A) It has high resistivity
(B) It does not oxidise readily at high temperature
(C) Both of the above
(D) None of the above 

Answer : C

Based on the given diagram, answer the questions given below :


In the given circuit, connect a nichrome wire of length ‘L’ between points X and Y and note the ammeter reading.

Question. In a circuit two resistors of 5 Ω and 10 Ω are connected in series. Compare the current passing through the two resistors.
(A) 1 : 2
(B) 1 : 3
(C) 2 : 1
(D) 1 : 1 

Answer : D

Question. When this experiment is repeated by inserting another nichrome wire of the same thickness but twice the length (2L), what changes are observed in the ammeter reading ?
(A) Ammeter reading will increase.
(B) Ammeter reading will decrease.
(C) Will show double the increase.
(D) No change in ammeter reading. 

Answer : B

Question. State the changes that are observed in the ammeter reading if we double the area of crosssection without changing the length in the above experiment.
(A) Ammeter reading will increase
(B) Ammeter reading will decrease
(C) Will decrease to half
(D) No change in ammeter reading 

Answer : A

Question. When nichrome and copper wire of same length and same radius are connected in series and current I is passed through them. Which wire gets heated up more?
(A) Nichrome wire
(B) Copper wire
(C) Both will heat up at the same temperature
(D) None of the wire will get heated up. 

Answer : A

In the given circuit, three identical bulbs B₁, B₂ and B₃ are connected in parallel with a battery of 4.5 V. Study the diagram and answer the questions given below :

Question. What will happen to the other two bulbs if the bulb B₃ gets fused ?
(A) They will also stop glowing.
(B) Other bulbs will glow with same brightness.
(C) They will glow with low brightness.
(D) They glow with more brightness. 

Answer : B

Question. How many resistors of 88 W are connected in parallel to carry 10 A current on a 220 V line ?
(A) 2 resistors
(B) 1 resistors
(C) 3 resistors
(D) 4 resistors 

Answer : D

Question. If the wattage of each bulb is 1.5 W, how much readings will the ammeter A show when all the three bulbs glow simultaneously?
(A) 1.0 A
(B) 2 A
(C) 1.5 A
(D) None of the above 

Answer : A

Question. Find the total resistance of the circuit.
(A) 1.0 Ω
(B) 4.5 Ω
(C) 1.5 Ω
(D) 2.0 Ω 

Answer : B

Study the given passage and answer the questions given below:

Two conductors A and B of resistances 5 Ω and 10 Ω respectively are first joined in parallel and then in series. In each case the voltage applied is 20 V.

Question. In which arrangement will the current through A and B be the same ?
(A) Series arrangement
(B) Parallel arrangement
(C) Both of the above
(D) None of the above 

Answer : A

Question. Equivalent resistance in parallel combination is:
(A) 15 Ω
(B) 3.33 Ω
(C) 0.3 Ω
(D) None of the above

Answer : B

Question. Which of these circuit diagram shows the correct connection when A and B are joined in parallel?

(D) None of these 

Answer : A

Question. In which combination will the voltage across the conductors A and B be the same ?
(A) Series arrangement
(B) Parallel arrangement
(C) Both of the above
(D) None of the above 

Answer : B

Study the given circuit diagram and answer the questions given below :

Question. Effective resistance of two 8 Ω resistors in the combination.
(A) 4 Ω
(B) 16 Ω
(C) 8 Ω
(D) 1 Ω 

Answer : A

Question. Potential difference across 4 Ω resistor is :
(A) 1V
(B) 2 V
(C) 4 V
(D) 8 V 

Answer : C

Question. Power dissipated in 4 Ω resistor is :
(A) 4 W
(B) 2 W
(C) 1 W
(D) 8 W 

Answer : A

Question. Current flowing through 4 Ω resistor is :
(A) 1 A
(B) 2 A
(C) 8 A
(D) 4 A 

Answer : A

Very Short Answer Type Questions :

Question. What does the cord of an electric oven not glow while its heating element does ?
Answer : Cord is made up of copper wire whereas heating element is made up of alloy.

Question. Write SI unit of resistivity.
Answer : Ohm metre (ohm m).

Question. What is meant by the statement. “The resistance of a conductor is one ohm” ?
Answer : The resistance of a conductor is said to be 1 ohm if a current of 1 ampere flows through it when the potential difference across it is 1 volt.

Question. Should the resistance of a voltmeter be low or high?
Give reason.
Answer : High. In parallel connection, less current passes through high resistance. 

Question. Write the mathematical expression for Joule’s law of heating. 
Answer : Mathematical expression of Joule’s law of heating is
: H = I²Rt
Where, H = Produced Heat
I = Current flowing through the device
t = Time of current flow
R = Resistance of the appliance

Question. Why are the heating elements of electric toasters and electric irons made of an alloy rather than a pure metal ?
Answer : Due to high resistivity of alloys rather than its constituting metals. 

Question. Two unequal resistances are connected in parallel. If you are not provided with any other parameters (eg. numerical values of I and R), what can be said about the voltage drop across the two resistors?
Answer : Voltage-drop is same across both.

Short Answer Type Questions :

Question. The current flowing through a resistor connected in a circuit and the potential difference developed across its ends are as shown in the diagram by milliammeter and voltmeter readings respectively.
(a) What are the least counts of these meters ?
(b) What is the resistance of the resistor ?

Answer : (a) least count of ammeter = 10 mA 
least count of voltmeter = 0.1 V 
(b) 2.4/0.25 = 9.6 ohm (250 mA = 0.25 A)

Question. A student has two resistors- 2 Ω and 3 Ω. She has to put one of them in place of R2 as shown in the circuit. The current that she needs in the entire circuit is exactly 9A. Show by calculation which of the two resistors she should choose 
Q.5 p.136
Answer : The overall current needed = 9A
The voltage is 12V
Hence by Ohm’s Law V=IR
The resistance for the entire circuit = 12/9 = 4/3 Ω = R
R₁ and R₂ are in parallel. Hence, R=(R₁ R₂)/(R₁ + R₂) or, 4R₂/(4+R₂) = 4/3
∴      R₂ = 2Ω 2

Question. While studying the dependence of potential difference (V) across a resistor on the current (I) passing through it, in order to determine the resistance of the resistor, a student took 5 readings for different values of current and plotted a graph between V and I. He got a straight line graph passing through the origin. What does the straight line signify? Write the method of determining resistance of the resistor using this graph.
Answer : The graph between V and I is a straight line and passes the origin, this verifies the Ohm’s law.

Or R = Value of potential differnce at a point/Value of current at the same point

Question. Define electric power. Write an expression relating electric power, potential difference and resistance.
Answer : Electric power : It is the amount of electric energy consumed in a circuit per unit time.
Expression : P = V₂/R   
Where, P = Electric Power, V = Potential difference, R = Resistance

Question. How many 132 Ω resistors in parallel are required to carry 5 A on a 220 V line ?
Answer : Given      V = 220 V, I = 5 A
                     V = IR
Or                 R = V/I
In parallel combination, let the no. of resistors = x
                            132/x = 220/5
or,                        132/x = 44
or,                               x = 132/44
∴                                x = 3
The number of resistors = 3 

Question. Compute the heat generated while transferring 96,000 coulomb of charge in two hours through a potential difference of 40 V. A
Answer : Given, Charge (Q)= 96000 C, Time (t) = 2 h, Potential difference (V) = 40 V
Heat generated, H = VIt                  (where I = Q/t)
                        H = d
                        H = V × Q
                        H = 40 ×96000
                        H = 384000 J