NCERT Solutions for class 12 Physics | Chapter 3 - Current Electricity

Questions
1 Two conductors of equal length and radii the ratio of 2 : 3 are; connected in parallel the source of electricity. The ratio of the velocity of electrons in the conductor be :
A 2 : 3
B 4 : 9
C 1 : 1
D 3 : 2

Answer:1 : 1
2 The smallest resistance that can be obtained by the combination of n resistors each resistance r is :
A r/n
B nr
C n/r
D n²r

Answer:r/n

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3 The charge flowing in a conductor varies with time as :

Class 12 Physics Chapter 3 Current Electricity

Where α, β, γ are positive constants. Then the initial current (l) is given by the condition :

A l = α
B l = α²
C l = α-1
D None of these

Answer:l = α
4 The specific resistance of a conductor increases with :
A increase in temperature
B increase in cross-sectional area
C decrease in length
D decrease in cross-sectional area

Answer:increase in temperature
5 How many joules are equal to I kWh ?
A 3.6 × 104
B 3.6 × 105
C 3.6 × 106
D None of these

Answer:3.6 × 106
6 The emf of a car battery is about:
A 2.5 V
B 4.5 V
C 8.6 V
D 12 V

Answer:12 V
7 Why is the Wheatstone bridge more accurate than other methods of measuring resistances: ‘
A It is a null method
B It is based on Kirchhoffs laws
C It has four resistances
D It does not involve ohm’s law

Answer:It is a null method
8 When three identical bulbs of 60 W, 200 V rating are connected in series to a 200 V supply, the power drawn by them will be:
A 20 W
B 60 W
C 180 W
D 10 W

Answer:20 W
9 Kirchhoffs first and second laws for electrical circuits are consequences of:
A conservation of energy
B conservation of electrical charge and energy respectively
C conservation of electric charge
D neither conservation of energy nor electric charge

Answer:conservation of electrical charge and energy respectively
10 How much electric energy is consumed by a 100 W lamp used for 6 hours everyday for 30 days?
A 18 kJ
B 18 kWh
C 1.8 J
D None of these

Answer:18 kWh
11 Two wires of copper are of the same length but’have different diameters. When they are connected in series across a battery, the heat generated is H1 When connected in parallel across the same battery, the heat generated during the same time is H2 Then :
A H1 = H2
B H1 < H2
C H1 > H2
D H1 > H2

Answer:H1 < H2
12 Siemen is the unit of:
A resistance
B conductance
C specific conductance
D None of these

Answer:conductance
13 The length of a conductor is halved. Its resistance will be :
A halved
B doubled
C unchanged
D quadrupled

Answer:halved
14 The specific resistance of a rod of copper as compared to that of thin wire of copper is :
A less
B more
C same
D depends upon the length and area of cross-section of the wire

Answer:same
15 Given three equal resistors, how many different combinations (taken all of them together) can be made?
A 3
B 4
C 5
D 6

Answer:4
16 The resistance of a human body is about:
A 12 Ω
B 120 Ω
C 12 KΩ
D 120 MΩ

Answer:12 KΩ
17 Specific resistance of ali metals is mostly affected by:
A temperature
B pressure
C magnetic field
D volume

Answer:temperature
18 In the above question, the conductance:
A halved
B doubled
C unchanged
D quadrupled

Answer:doubled
19 Suppose H1 is the heat generated per second in the filament of a 100 W, 250 V lamp and H2 is the heat generated in the filament of a 200 W, 250 V lamp. Then H1/H2 is equal to:
A 1
B 2
C 1/2
D 1/4

Answer:1/2
20 A 5 A fuse wire can with stand a maximum power of 1 W in circuit. The resistance of the fuse wire is:
A 0.2 Ω
B 5 Ω
C 0.4 Ω
D 0.04 Ω

Answer:0.04 Ω

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