# MCQ Questions for Class 12 Physics Chapter 3 Current Electricity with Answers

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## Current Electricity Class 12 MCQs Questions with Answers

Solve this Current Electricity Multiple Choice Questions of Class 12 Physics Chapter 3 MCQ, so as not to miss out on any concept from being clear about what they mean!

Multiple-Choice Questions

Question 1.
Which of the following characteristics of electrons determines the current in a conductor?
(a) Drift velocity alone.
(b) Thermal velocity alone.
(c) Both drift velocity and thermal velocity.
(d) Neither drift nor thermal velocity.

Question 2.
Kirchhoff’s junction rule is a reflection of
(a) conservation of current density vector.
(b) conservation of charge.
(c) the fact that the momentum with which a charged particle approaches a junction is unchanged (as a vector) as the charged particle leaves the junction.
(d) the fact that there is accumulation of charges at a junction.

Question 3.
In a metre bridge the point D is a neutralb point as shown in the figure. (a) The metre bridge will have at least two neutral points for this set of resistances.
(b) When the jockey contacts a point on metre wire left of D, current flows to B from the wire.
(c) When the jockey contacts a point on the metre wire to the right of D, current flows from B to the wire through galvanometer.
(d) When R is increased, the neutral point shifts to left.

Answer: (c) When the jockey contacts a point on the metre wire to the right of D, current flows from B to the wire through galvanometer.

Question 4.
Two cells of emfs approximately 5 V and 10 V are to be accurately compared using a potentiometer of length 400 cm.
(a) The battery that runs the potentiometer should have voltage of 8 V.
(b) The battery of potentiometer can have a voltage of 15 V and R adjusted so that the potential drop across the wire slightly exceeds 10 V.
(c) The first portion of 50 cm of wire itself should have a potential drop of 10 V.
(d) Potentiometer is usually used for comparing resistances and not voltages.

Answer: (b) The battery of potentiometer can have a voltage of 15 V and R adjusted so that the potential drop across the wire slightly exceeds 10 V.

Question 5.
A resistance R is to be measured using a meter bridge. A student chooses the standard resistance S to be 100 Ω. He finds the null point at l1 = 2.9 cm. He is told to attempt to improve the accuracy. Which of the following is a useful way?
(a) He should measure l1 more accurately.
(b) He should change S to 1000 Ω and repeat the experiment.
(c) He should change S to 3 Ω and repeat the experiment.
(d) He should give up hope of a more accurate measurement with a meter bridge.

Answer: (c) He should change S to 3 Ω and repeat the experiment.

Question 6.
The temperature co-efficient of resistance of a wire is 0.00125 °C-1. At 300 K its resistance is 1 Ω. The resistance of the wire will be 2 Ω at
(a) 1154 K
(b) 1127 K
(c) 600 K
(d) 1400 K

Question 7.
Masses of three wires are in the ratio 1 : 3 : 5 and their lengths are in the ratio 5 : 3 : 1. The ratio of their electrical resistance is
(a) 1 : 3 : 5
(b) 5 : 3 : 1
(c) 1 : 15 : 125
(d) 125 : 15 : 1

Answer: (d) 125 : 15 : 1

Question 8.
A battery of internal resistance 4 Ω is connected to the network of resistances as shown. In order to give the maximum power to the network, the value of R (in Ω) should be (a) 4/9
(b) 8/9
(c) 2
(d) 18

Question 9.
Two batteries A and B each of emf 2 volt are connected in series to external resistance R = 1 Ω. Internal resistance of A is 1.9 Ω and that of B is 0.9 Ω. What is the potential difference between the terminals of battery A? (a) 2 V
(b) 3.8 V
(c) 0
(d) None of these

Question 10.
A potentiometer wire is 100 cm long and a constant potential difference is maintained across it. Two cells are connected in series first to support one another and then in opposite direction. The balance points are obtained at 50 cm and 10 cm from the positive end of the wire in the two cases. The ratio of emfs is
(a) 5 : 1
(b) 5 : 4
(c) 3 : 4
(d) 3 : 2

Fill in the blanks

Question 1.
The magnitude of ……………. current remains the same throughout the flow of current.

Question 2.
……………. current magnitude changes with time.

Question 3.
The current whose magnitude and direction change with time is called ……………

Question 4.
…………… velocity is the average velocity with which the free electrons get drifted inside a conductor under the effect of the electric field, opposite to the direction of the field.

Question 5.
…………. time is the time during which the electrons do not undergo collisions.

Question 6.
The value of drift velocity is very small, of the order of ……………..

Answer: 0.1 cm s-1 to 1.0 cm s-1

Question 7.
The relation between drift velocity and electric field is ……………

Answer: vd = $$\frac { eE }{m}$$ τ

Question 8.
……………. of electron is defined as the drift velocity gained by an electron per unit electric field.

Question 9.
The current per unit cross-sectional area is called current …………….

Question 10.
An electron travels along a …………… line in the absence of an electric field.

Question 11.
An electron travels along a …………… line in the presence of an electric field.

Question 12.
Electric current flowing through conductor is …………… proportional to the drift velocity.

Question 13.
When a wire of resistance R is drawn to n times the original length, then its resistance becomes …………..

Question 14.
………….. depends only on the nature of material of the conductor and not on the dimensions of the conductor.

Question 15.
Resistivity of an ……………. is greater than the resistivity of its constituents.

Question 16.
The resistance of a resistor marked with bands of colour yellow, violet, brown and gold is ………….

Answer: 470 Ω ± 5 %

Question 17.
When resistors are connected in series, the net resistance is the …………… of individual resistances.

Question 18.
When resistors are connected in parallel, the reciprocal of net resistance is the sum of the ……………. of individual resistances.

Question 19.
When resistors are connected in series, the …………… through each resistor is same.

Question 20.
Current in the circuit is ……………. of the relative positions of the resistors in series.

Question 21.
A cell of emf E and resistance r is connected across an external resistance R. The potential difference across the terminals of a cell for r = R is …………..

Question 22.
A Wheatstone bridge is most sensitive when all the resistances are of ……………

Question 23.
As per Kirchhoff’s II law, the algebraic sum of emfs is equal to algebraic sum of product of ……………

Question 24.
A battery of emf 2 volt and internal resistance 0.1 Q is being charged with a current of 5 A. The p.d. between the two terminals of the battery is …………. volt.

Question 25.
In a Wheatstone bridge, the balance of the bridge is not affected on ……………. the positions of the battery and the galvanometer.

Question 26.
The potential difference of the cell in an open circuit is called ……………

Question 27.
The emf of the cell is always …………….. than the terminal potential difference of the cell when current is drawn from the cell.