Class 12 Physics Chapter 3 Current Electricity Solved Question Answers

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

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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

View Answer

Answer:r/n

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

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

View Answer

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

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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

View Answer

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

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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

View Answer

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

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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

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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

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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

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Answer:H₁ < H₂

12 Siemen is the unit of:

A resistance

B conductance

C specific conductance

D None of these

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Answer:conductance

13 The length of a conductor is halved. Its resistance will be :

A halved

B doubled

C unchanged

D quadrupled

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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

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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

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Answer:4

16 The resistance of a human body is about:

A 12 Ω

B 120 Ω

C 12 KΩ

D 120 MΩ

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Answer:12 KΩ

17 Specific resistance of ali metals is mostly affected by:

A temperature

B pressure

C magnetic field

D volume

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Answer:temperature

18 In the above question, the conductance:

A halved

B doubled

C unchanged

D quadrupled

View Answer

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

View Answer