CBSE Class 12 Physics Current Electricity Worksheet Set D

CBSE Class 12 Physics Current Electricity. Students can download these worksheets and practice them. This will help them to get better marks in examinations. Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects. 

1 Two wires of equal length, one of copper and the other of manganin have the same resistance. Which wire is thicker?

2 A wire of resistance 8R is bent in the form of a circle. What is the effective resistance between the ends of a diameter AB?

3 When electrons drift in a metal from lower to higher potential, does it mean that all the ‘free’ electrons of the metal are moving in the same direction?

4 Two identical slabs, of a given metal, are joined together, in two different ways, as shown in figures (a) and (b). What is the ratio of the resistances of these two combinations?

5 A cylindrical metallic wire is stretched to increase its length by 5%. Calculate the percentage change in its resistance.
 

Important Questions for NCERT Class 12 Physics Current Electricity

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

Answer  A
 

Question. The cold junction of a thermocouple is maintained at 10ºC. No thermo e.m.f. is developed when the hot junction is maintained at 530ºC. The neutral temperature is    
(a) 260ºC
(b) 265ºC
(c) 270ºC
(d) 520ºC

Answer  C


Question. A heating coil is labelled 100 W, 220 V. The coil is cut in half and the two pieces are joined in parallel to the same source. The energy now liberated per second is   
(a) 200 W
(b) 400 W
(c) 25 W
(d) 50 W

Answer  B
 

Question. Three resistances each of 4 W are connected to form a triangle. The resistance between any two terminals is   
(a) 12 W
(b) 2 W
(c) 6 W
(d) 8/3 W

Answer  D
 

Question. You are given several identical resistances each of value R = 10 W and each capable of carrying a maximum current of one ampere. It is required to make a suitable combination of these resistances of 5 W which can carry a current of 4 ampere. The minimum number of resistances of the type R that will be required for this job is   
(a) 4
(b) 10
(c) 8
(d) 20 

Answer  C


Question. 40 electric bulbs are connected in series across a 220 V supply. After one bulb is fused the remaining 39 are connected again in series across the same supply. The illumination will be    
(a) more with 40 bulbs than with 39
(b) more with 39 bulbs than with 40
(c) equal in both the cases
(d) in the ratio 402 : 392. .

Answer  B


Question. n equal resistors are first connected in series and then connected in parallel. What is the ratio of the maximum to the minimum resistance ?   
(a) n
(b) 1/n²
(c) n²
(d) 1/n

Answer  C
 

Question. The resistance of a galvanometer is 50 W and current required to give full scale deflection is 100 μA in order to convert it into an ammeter for reading upto 10 A. It is necessary to put an resistance of    
(a) 3.5 × 10^–4 Ω
(b) 10 × 10^–4 Ω
(c) 2.5 × 10^–4 Ω
(d) 5 × 10^–4 Ω

Answer  D


Question. The electro-chemical equivalent of a substance is numerically equal to the mass of the substance deposited if a current I flows through the electrolyte for 0.25 seconds. The value of I is :   
(a) 1 A 
(b) 2 A 
(c) 3 A
(d) 4 A

Answer  D


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 W
(b) 40/3 W
(c) 40 W
(d) 100 W

Answer  C
 

Question. Consider the following two statements.    
(A) Kirchhoff’s junction law follows from the conservation of charge.
(B) Kirchhoff’s loop law follows from the conservation of energy. Which of the following is correct?
(a) Both (A) and (B) are wrong.
(b) (A) is correct and (B) is wrong.
(c) (A) is wrong and (B) is correct.
(d) Both (A) and (B) are correct.

Answer   D

Question. Four wires of the same diameter are connected in turn between two points, maintained at a constant potential difference. Their resistivities are; r and L (wire 1)., 1.2r and 1.2 L (wire 2), 0.9 r and 0.9L (wire 3) and r and 1.5 L (wire 4). Rank the wires according to the rates at which energy is dissipated as heat, greatest first    
(a) 4 > 3 > 1 > 2
(b) 4 > 2 > 1 > 3
(c) 1 > 2 > 3 > 4
(d) 3 > 1 > 2 > 4

Answer   D
 

Question. Kirchhoff’s first and second laws of electrical circuits are consequences of    
(a) conservation of energy and electric charge respectively
(b) conservation of energy
(c) conservation of electric charge and energy respectively
(d) conservation of electric charge

Answer   C. 


Question. Kirchhoff’s first law, i.e. S i = 0 at a junction, deals with the conservation of    
(a) momentum
(b) angular momentum
(c) charge
(d) energy

Answer   C
 

Question. The resistances 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) 0.1 A
(b) 2.0 A
(c) 1.0 A
(d) 0.2 A 

Answer   D

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