CBSE Class 12 Physics Current Electricity Worksheet Set D

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. If each resistance in the figure is of 9Ω then reading of ammeter is:

a. 5 A
b. 8 A
c. 2 A
d. 9 A
Answer : A

Question. A wire has resistance 12Ω. It is bent in the form of a circle. The effective resistance between the two points on any diameter is equal to:
a. 12 Ω
b. 6 Ω
c. 3 Ω
d. 24 Ω
Answer : C ​

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. 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 Ω. The total resistance of the combination is   
(a) 5/2 Ω
(b) 40/3 Ω
(c) 40 Ω
(d) 100 Ω
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. Consider the circuit shown in the figure. The current i3 is equal to:

a. 5 amp
b. 3 amp
c. – 3 amp
d. – 5/6 amp
Answer : D

Question. The scale of a galvanometer of resistance 100Ω contains 25 divisions. It gives a deflection of one division on passing a current of 4 x 10⁻⁴ A. The resistance in ohms to be added to it, so that it may become a voltmeter of range 2.5 volt is:
a. 100
b. 150
c. 250
d. 300
Answer : B

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. 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. The equivalent resistance between A and B in the circuit shown will be:

a. (5/4)r
b. (6/5)r
c. (7/6)r
d. (8/7)r
Answer : D

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

Question. The equivalent resistance between points A and B of an infinite network of resistance, each of 1Ω, connected as shown is:

a. Infinite
b. 2 Ω
c. (1 + √5 / 2) Ω 
d. Zero
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. In the given figure, equivalent resistance between A and B will be:

a.(14/3) Ω
b. (3/14) Ω
c. (9/14) Ω
d. (14/9) Ω
Answer : A

Question. In a mixed grouping of identical cells 5 rows are connected in parallel by each row contains 10 cell. This combination send a current i through an external resistance of 20Ω. If the emf and internal resistance of each cell is 1.5 volt and 1 Ω respectively then the value of i is:
a. 0.14
b. 0.25
c. 0.75
d. 0.68
Answer : D

Question. A galvanometer, having a resistance of 50 Ω gives a full scale deflection for a current of 0.05 A. the length in meter of a resistance wire of area of cross-section 2.97 × 10^–2cm² that can be used to convert the galvanometer into an ammeter which can read a maximum of 5A current is: (Specific resistance of the wire = 5 × 10^–7 Ωm)
a. 9
b. 6
c. 3
d. 1.5
Answer : C

Question. 100 mA current gives a full scale deflection in a galvanometer of resistance 2Ω. The resistance connected with the galvanometer to convert it into a voltmeter of 5 V range is:
a. 98 Ω
b. 52 Ω
c. 80 Ω
d. 48 Ω
Answer : D

Question. To get maximum current in a resistance of 3 Ω one can use n rows of m cells connected in parallel. If the total no. of cells is 24 and the internal resistance of a cell is 0.5 then:
a. m = 12, n = 2
b. m = 8, n = 4
c. m = 2, n = 12
d. m = 6, n = 4
Answer : A

Question. 100 cells each of emf 5V and internal resistance 1Ω are to be arranged so as to produce maximum current in a 25Ω resistance. Each row contains equal number of cells. The number of rows should be:
a. 2
b. 4
c. 5
d. 100
Answer : A

Question. n identical cells, each of emf E and internal resistance r, are joined in series to form a closed circuit. The potential difference across any one cell is:
a. Zero
b. E
c. E/n
d. (n - 1 / n ) E
Answer : A

Question. In the adjoining circuit, the battery E₁ has as emf of 12 volt and zero internal resistance, while the battery E has an emf of 2 volt. If the galvanometer reads zero, then the value of resistance X ohm is:

a. 10
b. 100
c. 500
d. 200
Answer : B

Question. A ammeter of range 10 mA has a coil of resistance 1Ω. To use it as voltmeter of range 10 volt, the resistance that must be connected in series with it will be:
a. 999 Ω
b. 99 Ω
c. 1000 Ω
d. None of these
Answer : A

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. In the following figure ammeter and voltmeter reads 2 amp and 120 volt respectively. Resistance of voltmeter is:

a. 100 #
b. 200 #
c. 300 #
d. 400 #
Answer : C

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