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

Question 1.

The speed at which tjie current travels in a conductor is nearly:

(a) 3 × 10^{4} ms^{-1}

(b) 3 × 10^{6} ms^{-1}

(c) 3 × 10^{8} ms^{-1}

(d) 3 × 10^{10} ms^{-1}

## Answer

Answer: (a) 3 × 10^{4} ms^{-1}

Question 2.

The resistance of a human body is about:

(a) 12 Ω

(b) 120 Ω

(c) 12 KΩ

(d) 120 MΩ

## Answer

Answer: (c) 12 KΩ

Question 3.

The number of electrons that constitute 1 A of current is:

(a) 6.25 × 10^{16}

(b) 6.25 × 10^{17}

(c) 6.25 × 10^{18}

(d) 6.25 × 10^{19}

## Answer

Answer: (c) 6.25 × 10^{18}

Question 4.

How many different resistances are possible with two equal resistors?

(a) 2

(b) 3

(c) 4

(d) 5

## Answer

Answer: (b) 3

Question 5.

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

Answer: (b) 4

Question 6.

Specific resistance of ali metals is mostly affected by:

(a) temperature

(b) pressure

(c) magnetic field

(d) volume

## Answer

Answer: (a) temperature

Question 7.

The example of a non-ohmic resistance is:

(a) copper wire

(b) fi lament lamp

(c) carbon resistor

(d) diode

## Answer

Answer: (d) diode

Question 8.

If a certain piece of copper is to be shaped into a conductor of minimum resistance, its length (L) and cross-sectional area (a) shall respectively be :

(a) L, 2A

(b) \(\frac{L}{2}\), 2A

(c) 2L, 2A

(d) 2l, \(\frac{A}{2}\)

## Answer

Answer: (b) \(\frac{L}{2}\), 2A

Question 9.

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

Answer: (c) same

Question 10.

A wire of resistance 3 Ω is cut into three pieces, which are then joined to form a triangle. The equivalent resistance between any corners of the triangle is :

(a) \(\frac{2}{3}\) Ω

(b) \(\frac{3}{2}\) Ω

(c) \(\frac{1}{2}\) Ω

(d) \(\frac{1}{3}\) Ω

## Answer

Answer: (a) \(\frac{2}{3}\) Ω

Question 11.

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

(a) halved

(b) doubled

(c) unchanged

(d) quadrupled

## Answer

Answer: (a) halved

Question 12.

In the above question, the conductance:

(a) halved

(b) doubled

(c) unchanged

(d) quadrupled

## Answer

Answer: (b) doubled

Question 13.

Siemen is the unit of:

(a) resistance

(b) conductance

(c) specific conductance

(d) None of these

## Answer

Answer: (b) conductance

Question 14.

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

Answer: (b) 18 kWh

Question 15.

Suppose H_{1} is the heat generated per second in the filament of a 100 W, 250 V lamp and H_{2} is the heat generated in the filament of a 200 W, 250 V lamp. Then H_{1}/H_{2} is equal to:

(a) 1

(b) 2

(c) \(\frac{1}{2}\)

(d) \(\frac{1}{4}\)

## Answer

Answer: (c) \(\frac{1}{2}\)

Question 16.

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 H_{1} When connected in parallel across the same battery, the heat generated during the same time is H_{2} Then :

(a) H_{1} = H_{2}

(b) H_{1} < H_{2}

(c) H_{1} > H_{2}

(d) H_{1} > H_{2}

## Answer

Answer: (b) H_{1} < H_{2}

Question 17.

In questions 135, w hen the wires are connected in series, the heat produced in the thinner wire is H_{1} and that in the thicker wire is H_{2}. Then :

(a) H_{1} = H_{2}

(b)H_{1} < H_{2}

(c) H_{1} > H_{2}

(d) H_{1} > H_{2}

## Answer

Answer: (c) H_{1} > H_{2}

Question 18.

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

Answer: (b) conservation of electrical charge and energy respectively

Question 19.

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

Answer: (d) 0.04 Ω

Question 20.

The length and radius of an electric resistance of a certain wire are doubled simultaneously, then the:

(a) resistance will be doubled and specific resistance will be halved

(b) resistance will be halved and specific resistance will remain uncharged

(c) resistance will be halved and the specific resistance will be doubled

(d) resistance and specific resistance will both remain uncharged

## Answer

Answer: (b) resistance will be halved and specific resistance will remain uncharged

Question 21.

A galvanometer acting as a volt meter will have with its coil.

(a) a high resistance in parallel

(b) a high resistance in series

(c) a low resistance in parallel

(d) a low resistance in series

## Answer

Answer: (b) a high resistance in series

Question 22.

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

Answer: (a) 20 W

Question 23.

n resistances, each of R Ω, are connected in parallel gives an equivalent resistance of R Ω. If these resistances were , connected in series, the combination would have a resistance in Ω is equal to

(a) n²R

(b) R/n²

(c) R/n

(d) nR

## Answer

Answer: (a) n²R

Question 24.

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

Answer: (a) It is a null method

Question 25.

A potential difference of 10 V is applied across a conductance of 2 S. The current in the conductor will be :

(a) 20 A

(b) 5 A

(c) 0.2 A

(d) None of these

## Answer

Answer: (a) 20 A

Question 26.

Ohm’s law is valid when the temperature of conductor is :

(a) very low

(b) very high

(c) varying

(d) constant

## Answer

Answer: (d) constant

Question 27.

The emf of a car battery is about:

(a) 2.5 V

(b) 4.5 V

(c) 8.6 V

(d) 12 V

## Answer

Answer: (d) 12 V

Question 28.

Emf is measured in :

(a) joule

(b) joule/coulomb

(c) joule-coulombs

(d) joule/coulomb/metre

## Answer

Answer: (b) joule/coulomb

Question 29.

1 kilowatt hour is commonly known as :

(a) unit

(b) 1 faraday

(c) 1 curie

(d) None of these

## Answer

Answer: (a) unit

Question 30.

How many joules are equal to I kWh ?

(a) 3.6 × 10^{4}

(b) 3.6 × 10^{5}

(c) 3.6 × 10^{6}

(d) None of these

## Answer

Answer: (c) 3.6 × 10^{6}

Question 31.

The temperature coefficient of resistance is expressed in :

(a) °C

(b) °C^{-1}

(c) m°C^{-1}

(d) None of these

## Answer

Answer: (b) °C^{-1}

Question 32.

Copper wire is used as connecting wire because :

(a) copper has high electrical resistivity

(b) copper has low electrical resistivity

(c) copper has low electrical conductivity

(d) copper has high value of elasticity

## Answer

Answer: (b) copper has low electrical resistivity

Question 33.

The heat sensitive device whose resistivity changes very rapidly with change of temperature is called a :

(a) resistor

(b) super-conductor

(c) thermocouple

(d) thermistor

## Answer

Answer: (d) thermistor

Question 34.

The phenomenon of super-conductivity was discovered by :

(a) Ohm

(b) Onnes

(c) Edison

(d) None of these

## Answer

Answer: (b) Onnes

Question 35.

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

Answer: (a) increase in temperature

Question 36.

In an experiment with potentiometer, null point with a cell is found at 240 cm. When the cell is shunted with a resistance 2 Ω, the null point becomes 120 cm internal resistance of cell is :

(a) 4 Ω

(b) 2 Ω

(c) 1 Ω

(d) \(\frac{1}{2}\) Ω

## Answer

Answer: (b) 2Ω

Question 37.

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

Answer: (c) 1 : 1

Question 38.

The charge flowing in a conductor varies with time as :

q = αt \(\frac{1}{2}\) βt² + \(\frac{1}{6}\) γt³

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

Answer: (a) l = α

Question 39.

In questions 38, the maximum value of current (l_{max}) is given by the condition :

(a) l_{max} = α – \(\frac{β^2}{2γ}\)

(b) l_{max} = α – \(\frac{β^2}{2α}\)

(c) l_{max} = α – \(\frac{γ^2}{2β}\)

(d) None of these

## Answer

Answer: (a) l_{max} = α – \(\frac{β^2}{2γ}\)

Question 40.

In questions 38, the line (t) after which the value of current reaches a maximum values given by :

(a) t = \(\frac{α}{β}\)

(b) t = \(\frac{β}{α}\)

(c) t = \(\frac{β}{γ}\)

(d) t = \(\frac{γ}{β}\)

## Answer

Answer: (a) t = \(\frac{α}{β}\)

Question 41.

In following figure shows currents in a part of electrical circuit, then the value of/(in ampere) is given by :

(a) 0.3 A

(b) 0.5 A

(c) 1.3 A

(d) None of these

## Answer

Answer: (a) 0.3 A

Question 42.

The smallest resistance that can be obtained by the combination of n resistors each resistance r is :

(a) \(\frac{r}{n}\)

(b) nr

(c) \(\frac{n}{r}\)

(d) n²r

## Answer

Answer: (a) \(\frac{r}{n}\)

Question 43.

Which of the following has a negative temperature coefficient of resistance ?

(a) Tungsten

(b) Carbon

(c) Nichrome

(d) Platinum

## Answer

Answer: (b) Carbon

Question 44.

An electric heating element consumes 500 W, when connected to a 100 V line. If the line voltage becomes 150 V, the power consumed Will be:

(a) 500 W

(b) 750 W

(c) 1000 W

(d) 1125 W

## Answer

Answer: (b) 750 W

Question 45.

A uniform w ire connected across a supply produces heat H per second. If wire is cut into three equal parts and all the parts are connected in parallel across the same supply, the heat produced per second will be :

(a) \(\frac{H}{9}\)

(b) 9 H

(c) 3 H

(d) \(\frac{H}{3}\)

## Answer

Answer: (d) \(\frac{H}{3}\)

Question 46.

In India electricity is supplied fordomestic use at 220 V. It is supplied at 110 V in U.S.A. If the resistance of a 60 W bulb use in India is R. the resistance of a 60 W bulb for use in USA will be:

(a) 2 R

(b) R

(c) R/2

(d) R/4

## Answer

Answer: (d) R/4

Question 47.

In the following figure represents a balanced Wheatstone bridge circuit. What is the value of X ?

(a) 15 Ω

(b) 20 Ω

(c) 25 Ω

(d) 30 Ω

## Answer

Answer: (c) 25 Ω

Question 48.

Two bulbs 25 W, 220 V and 100 W, 220 V are given. Which has higher resistance?

(a) 25 W

(b) 100 W

(c) both bulbs have equal resistance

(d) resistance of bulbs can not be compared

## Answer

Answer: (a) 25 W

Question 49.

Potentiometer measures the potential difference more accurately than a voltmeter because:

(a) It has a wire of high resistance

(b) It has a wire of low resistance

(c) It does not draw current from external circuit

(d) It draws heavy current from external circuit

## Answer

Answer: (c) It does not draw current from external circuit

Question 50.

In a Wheatstone bridge, the resistance each arm is 10 Ω. If the resistance galvanometers is also 10 Ω, then effective resistance of the bridge will be :

(a) 40 Ω

(b) 20 Ω

(c) 10 Ω

(d) 5 Ω

## Answer

Answer: (c) 10 Ω

Question 51.

The resistance of an aluminium wire is/i. It is stretched to /i times its original length. Its new resistance will be :

(a) nr

(b) n²r

(c) \(\frac{n^2}{r}\)

(d) \(\frac{r}{n^2}\)

## Answer

Answer: (b) n²r

Question 52.

A wire P is half the diameter and half the length of a wire Q of similar material. The ratio of resistances of P to that 0 is:

(a) 4 : 1

(b) 8 : 1

(c) 2 : 1

(d) 1 : 2

## Answer

Answer: (c) 2 : 1

Question 53.

What is the resistance across A and B in the network in Fig.?

(a) R

(b) 2 R

(c) \(\frac{R}{2}\)

(d) 6 R

## Answer

Answer: (a) R

Question 54.

When the wires are connected in parallel, the heat produced in the thinner wire is H_{1} and that in the thicker wire is H_{2} Then:

(a) H_{1} = H_{2}

(b) H_{1} < H_{2}

(c) H_{1} > H_{2}

(d) H_{1} ≥ H_{2}

## Answer

Answer: (b) H_{1} < H_{2}

Question 55.

Two equal resistors are connected in series across a battery and consume a power of P. If these are connected in parallel, then the’ power consumed will be:

(a) 2P

(b) 4P

(c) \(\frac{p}{4}\)

(d) P

## Answer

Answer: (b) 4P

Question 56.

Thermo electricity was discovered by:

(a) Joule

(b) Peitier

(c) Thomson

(d) Seebeck

## Answer

Answer: (d) Seebeck

Question 57.

Thermo emf is the order of:

(a) 10 V

(b) 10^{-3} V

(c) 10^{-6} V

(d) 10^{-12} V

## Answer

Answer: (c) 10^{-6} V

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