CBSE Class 12 Physics Current Electricity Worksheet Set A

Question. In the given circuit, as the sliding contact C is moved from A to B
(a) the readings of both the ammeter and the voltmeter remain constant
(b) the reading of both the ammeter and the voltmeter increase
(c) the reading of the ammeter remains constant but that of the voltmeter increases
(d) the reading of the ammeter remains constant but that of the voltmeter decreases

Answer: C

Question. The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Ω is
(a) 0.5 Ω
(b) 0.8 Ω
(c) 1.0 Ω
(d) 0.2 Ω

Answer: A

Question. A capacitor of 10m F has a pot. difference of 40 volts across it. If it is discharged in 0.2 second, the average current during discharge is
(a) 2 m A
(b) 4 m A
(c) 1 m A
(d) 0.5 m A

Answer: A

Question. A wire X is half the diameter and half the length of a wire Y of similar material. The ratio of resistance of X to that of Y is
(a) 8 : 1
(b) 4 : 1
(c) 2 : 1
(d) 1 : 1

Answer: C

Question. Potentiometer measures potential more accurately because
(a) it measures potential in open circuit
(b) it uses sensitive galvanometer for null deflection
(c) it uses high resistance potentiometer wire
(d) it measures potential in closed circuit

Answer: A

Question. Two identical fuses are rated at 10 A. If they are joined
(A) in parallel, the combination acts as a fuse of rating 20 A
(B) in parallel, the combination acts as a fuse of rating 5 A
(C) in series, the combination acts as a fuse of rating 10 A
(D) in series, the combination acts as a fuse of rating 20 A
Select the correct options.
(a) A, B
(b) A, C
(c) B, D
(d) B, C, D

Answer: B

Question. A current source drives a current in a coil of resistance R1 for a time t. The same source drives current in another coil of resistance R2 for same time. If heat generated is same, find internal resistance of source.
(a) R₁R₂/R₁ + R₂
(b) R₁ + R₂
(c) zero
(d) √R₁R²

Answer: D

Question. In which of the following the power dissipation is proportional to the square of the current ?
(a) Peltier effect
(b) Joule's effect
(c) Thomson effect
(d) None of the above

Answer: B

Question. When current is passed through a junction of two dissimilar metals, heat is evolved or absorbed at the junction. This process is called
(a) Seebeck effect
(b) Joule effect
(c) Petlier effect
(d) Thomson effect

Answer: C

Question. You are given a resistance coil and a battery. In which of the following cases is largest amount of heat generated ?
(a) When the coil is connected to the battery directly
(b) When the coil is divided into two equal parts and both the parts are connected to the battery in parallel
(c) When the coil is divided into four equal parts and all the four parts are connected to the battery in parallel
(d) When only half the coil is connected to the battery

Answer: C

Question. The electric resistance of a certain wire of iron is R. If its length and radius are both doubled, then
(a) the resistance and the specific resistance, will both remain unchanged
(b) the resistance will be doubled and the specific resistance will be halved
(c) the resistance will be halved and the specific resistance will remain unchanged
(d) the resistance will be halved and the specific resistance will be doubled

Answer: C

Question. A given resistor has the following colour scheme of the various strips on it : Brown, black, green and silver. Its value in ohm is
(a) 1.0´104 ±10%
(b) 1.0´105 ±10%
(c) 1.0´106 ±10%
(d) 1.0´107 ±10%

Answer: C

Question. A 12 cm wire is given a shape of a right angled triangle ABC having sides 3 cm, 4 cm and 5 cm as shown in the figure.
The resistance between two ends (AB, BC, CA) of the respective sides are measured one by one by a multi-meter. The resistances will be in the ratio of
(a) 3 : 4 : 5
(b) 9 : 16 : 25
(c) 27 : 32 : 35
(d) 21 : 24 : 25

Answer: C

Question. An electric lamp is marked 60 W, 220 V. The cost of kilo watt hour of electricity is Rs. 1.25. The cost of using this lamp on 220 V for 8 hours is
(a) Re 0.25
(b) Re 0.60
(c) Re 1.20
(d) Re 4.00

Answer: B

Question. A potentiometer consists of a wire of length 4m and resistance 10Ω. It is connected to a cell of e.m.f. 3V. The potential gradient of wire is
(a) 5V/m
(b) 2V/m
(c) 5V/m
(d) 10V/m

Answer: A

Question. If R₁ and R₂ are respectively the filament resistances of a 200 watt bulb and a 100 watt bulb designed to operate on the same voltage
(a) R₁ is two times R₂
(b) R₂ is two times R₁
(c) R₂ is four times R₁
(d) R₁ is four times R₂

Answer: B

Question. Two wires A and B of the same material, having radii in the ratio 1 : 2 and carry currents in the ratio 4 : 1. The ratio of drift speed of electrons in A and B is
(a) 16 : 1
(b) 1 : 16
(c) 1 : 4
(d) 4 : 1

Answer: A

Question. Two wires of same metal have the same length but their cross-sections are in the ratio 3 : 1. They are joined in series.
The resistance of the thicker wire is 10 W. The total resistance of the combination is
(a) 5/2 Ω
(b) 40/3 Ω
(c) 40 Ω
(d) 100 Ω

Answer: C

Question. Two electric bulbs whose resistance are in the ratio 1 : 2 are arranged 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. A flow of 107 electrons per second in a conducting wire constitutes a current of
(a) 1.6 x 10^-26A
(b) 1.6 x 10²⁶A
(c) 1.6 x 10^-12A
(d) 1.6 x 10¹²A

Answer: C

Q.1 The sequence of bands marked on a carbon resistor is red, red. Red silver. What is the value of resistance?

Ans:‐ 22×10²±10%

Q.2 . A wire is cut into half. What is the effect on its specific resistance?

Ans :‐ No effect.

Q.3 :‐ Why do we prefer a potentiometer with a longer bridge wire?

Ans:‐ When the bridge wire is longer the potential gradient is smaller. Smaller the potential gradient more is the sensitivity of potentiometer wire.

Q.4 What are the factors affecting internal resistance of a cell

Ans-Nature of electrolyte Separation between the electrode

Question. A torch bulb rated as 4.5 W, 1.5 V is connected as shown in fig. The e.m.f. of the cell, needed to make the bulb glow at full intensity is 

(a) 4.5 V
(b) 1.5 V
(c) 2.67 V
(d) 13.5 V

Answer: D

Question. A 100-W bulb and a 25-W bulb are designed for the same voltage. They have filaments of the same length and material. The ratio of the diameter of the 100-W bulb to that of the 25-W bulb is
(a) 4 : 1
(b) 2 : 1
(c) √2 :1
(d) 1 : 2

Answer: B

Question. In a metre bridge, the balancing length from the left end (standard resistance of one ohm is in the right gap) is found to be 20 cm. The value of the unknown resistance is
(a) 0.8 Ω
(b) 0.5 Ω
(c) 0.4 Ω
(d) 0.25 Ω

Answer: D

Question. An electric fan and a heater are marked as 100 W, 220 V and 1000 W, 220 V respectively. The resistance of heater is
(a) equal to that of fan
(b) lesser than that of fan
(c) greater than that of fan
(d) zero

Answer: B

Question. In an electroplating experiment, m g of silver is deposited when 4 A of current flows for 2 minutes. The amount in g of silver deposited by 6 A of current for 40 seconds will be
(a) 4 m
(b) 2 m
(c) m/2
(d) m/4

Answer: C

Question. In the circuit shown below, if the resistance of voltmeter is 4 kW, then the error in the reading of voltmeter will be 

(a) 50%
(b) 68%
(c) 17%
(d) 33.3%

Answer: D

Question. A steady current of 5 A is maintained for 45 minutes. During this time it deposits 4.572 g of zinc at the cathode of voltameter.
E.C.E. of zinc is
(a) 3.387 × 10^–4 g/C
(b) 3.387 × 10^–4 kg/C
(c) 3.384 × 10^–4 kg/C
(d) 3.384 × 10^–3 kg/C

Answer: A

Question. In a neon gas discharge tube Ne⁺ ions moving through a cross-section of the tube each second to the right is 2.9 × 10¹⁸, while 1.2 × 10¹⁸ electrons move towards left in the same time; the electronic charge being 1.6 × 10^–19 C, the net electric current is
(a) 0.27 A to the right
(b) 0.66 A to the right
(c) 0.66 A to the left
(d) zero

Answer: B

Question. Three copper wires of lengths and cross sectional areas are (l, A), (2 l, A/2) and (l/2, 2A). Resistance is minimum in
(a) wire of cross-sectional area A/2
(b) wire of cross-sectional area A
(c) wire of cross-sectional area 2A
(d) same in all the three cases

Answer: C

Question. A 4 ohm resistance wire is bent through 180º at its mid point and the two halves are twisted together. Then the resistance is
(a) 1 Ω
(b) 2 Ω
(c) 5 Ω
(d) 8 Ω

Answer: A

Question. When a current I is set up in a wire of radius r, the drift velocity is vd. If the same current is set up through a wire of radius 2 r, the drift velocity will be
(a) 4 v_d
(b) 2 v_d
(c) v_d/2
(d) v_d/4

Answer: D

Question. If nealy 10⁵ coulomb are liberated by 1gm equivalent of aluminium, then amount of aluminium (equivalent weight 9) deposited through electrolysis in 20 minutes by a current of 50 ampere will be :
(a) 0.6 gm.
(b) 0.09 gm
(c) 5.4 gm
(d) 10.8 gm

Answer: C

Question. The amount of charge Q passed in time t through a crosssection of a wire is Q = 5 t² + 3 t + 1.
The value of current at time t = 5 s is
(a) 9 A
(b) 49 A
(c) 53 A
(d) None of these

Answer: C

Question. Two identical cells connected in series send 1.0A current through a 5 Ω resistor. When they are connected in parallel, they send 0.8 A current through the same resistor. What is the internal resistance of the cell?
(a) 0.5 Ω
(b) 1.0 Ω
(c) 1.5 Ω
(d) 2.5 Ω

Answer: D

Question. If the resistance of a conductor is 5Ω at 50º C & 7Ω at 100º C, then mean temperature coefficient of resistance (of material) is
(a) 0.013/ ºC
(b) 0.004/ ºC
(c) 0.006/ ºC
(d) 0.008/ ºC

Answer: A

Question. If negligibly small current is passed though a wire of length 15 m & resistance of 5Ω, having uniform cross section of 6 × 10^–7 m², then coefficient of resistivity of material is
(a) 1×10^–7Ω–m
(b) 2×10^–7Ω–m
(c) 3×10^–7Ω–m
(d) 4×10^–7Ω–m

Answer: B

Question. The resistance of a wire at room temperature 30°C is found to be 10 W. Now to increase the resistance by 10%, the temperature of the wire must be [ The temperature coefficient of resistance of the material of the wire is 0.002 per °C]
(a) 36°C
(b) 83°C
(c) 63°C
(d) 33°C

Answer: B

Question. The resistance of the four arms P, Q, R and S in a Wheatstone’s bridge are 10 ohm, 30 ohm, 30 ohm and 90 ohm, respectively. The e.m.f. and internal resistance of the cell are 7 volt and 5 ohm respectively. If the galvanometer resistance is 50 ohm, the current drawn from the cell will be
(a) 0.2 A
(b) 0.1 A 
(c) 2. 0 A
(d) 1. 0 A

Answer: A

Question. The four wires from a larger circuit intersect at junction A as shown. What is the magnitude and direction of the current between points A and B ?
(a) 2 A from A to B
(b) 2A from B to A
(c) 3A from A to B
(d) 2A from B to A

Answer: C

Question. The resistance of the coil of an ammeter is R. The shunt required to increase its range n-fold should have a resistance
(a) R/n
(b) R/n-1
(c) R/n+1
(d) nR

Answer: B

Question. A cell of internal resistance r is connected across an external resistance nr. Then the ratio of the terminal voltage to the emf of the cell is
(a) 1/n
(b) 1/n+1
(c) n/n+1
(d) n-1/n

Answer: C

Question. A battery of e.m.f. 10 V and internal resistance 0.5 W is connected across a variable resistance R. The value of R for which the power delivered in it is maximum is given by
(a) 0.5 Ω
(b) 1.0 Ω
(c) 2.0 Ω
(d) 0.25 Ω

Answer: A

Question. The deflection in a galvanometer decreases from 25 divisions to 5 divisions when a resistor of 20Ω is connected in series.
Find resistance of galvanometer.
(a) 4 Ω
(b) 5 Ω
(c) 6 Ω
(d) 7 Ω

Answer: B

Question. A galvanometer of 50 ohm resistance has 25 divisions. A current of 4 × 10–4 ampere gives a deflection of one division. To convert this galvanometer into a voltmeter having a range of 25 volts, it should be connected with a resistance of
(a) 2450 Ω in series.
(b) 2500 Ω in series.
(c) 245 Ω in series.
(d) 2550 Ω in series.

Answer: A

Question. In the equation AB = C, A is the current density, C is the electric field, Then B is
(a) resistivity
(b) conductivity
(c) potential difference
(d) resistance

Answer: A

1 The resistance of the platinum wire of a platinum resistance thermometer at the ice point is 5Ωand at steam point is 5.23Ωwhen the thermometer is inserted in a hot bath, the resistance of the platinum wire is 5.795Ω. Calculate the temperature of the bath.

2 Find the effective resistance when resistances are connected in series 

3 Find the effective resistance when resistances are connected in parallel. 

4 Explain why a transformer is required to lower the voltage to a value suitable for use at a station? 

5 Derive the expression to find the power dissipated when current I is allowed to flow through a conductor? 

6 What is an emf of a cell? Derive an expression to find the current flowing in a circuit in which a resistor R is connected across a cell of emf ε. 

7 Derive an expression to find the effective emf of cells in series

8 Derive an expression to find the effective emf of cells in parallel 

9 State Kirchhoff’s rules. 

10 What is a Wheatstone Bridge? What is the advantage of it?