Science · Effects of current · chapter 11 of 13

Class 10 Science Chapter 11: Electricity MCQs with answers

10 multiple-choice questions on Electricity, each with its answer and the reason, written from the NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter.

Question 1
A charge of 270 C passes through the heating coil of a hair dryer in 1.5 minutes. The current in the coil is
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Answer: (a) 3 A

I = Q/t = 270 C / (1.5 × 60 s) = 270/90 = 3 A, and 1 A = 1 C/s. 180 A leaves the time in minutes; 0.33 A divides t by Q; 405 A multiplies Q by t.

Question 2
Leela sets up a circuit to study a resistor. Meter M₁ is joined in line with the resistor, so that the whole current passes through it; meter M₂ is joined between the two ends of the resistor. M₁ and M₂ must be, respectively,
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Answer: (c) an ammeter and a voltmeter

An ammeter is always connected in series with the part whose current it measures; a voltmeter is always connected in parallel across the two points whose potential difference it measures.

Question 3
The total charge carried by 2.5 × 10¹⁹ electrons is
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Answer: (a) 4 C

Each electron carries 1.6 × 10⁻¹⁹ C, so Q = 2.5 × 10¹⁹ × 1.6 × 10⁻¹⁹ C = 4 C.

Question 4
When 30 C of charge flows through the load of an inverter battery, 360 J of electrical energy is converted. The potential difference across the load is
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Answer: (d) 12 V

V = W/Q = 360 J / 30 C = 12 J/C = 12 V. Multiplying (10800) or inverting the ratio (0.083) are the usual slips.

Question 5
Ankit slides the switch of a lit torch to OFF and the bulb goes out at once. This happens because
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Answer: (c) the closed path is broken, so the current stops

A circuit is a continuous closed path; opening the switch breaks it, the current stops and the bulb does not glow. The cells keep their potential difference, and electrons are not used up.

Question 6
In the copper wire of a torch circuit, electrons drift from the negative terminal of the cell, through the bulb, towards the positive terminal. By convention, the electric current in that wire
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Answer: (c) flows from the positive terminal through the bulb to the negative terminal

Conventional current is taken opposite to the flow of electrons, so in the external circuit it is shown from the positive terminal to the negative terminal.

Question 7
Meena keeps a manganin wire at room temperature and measures the current through it for several values of potential difference. Her graph of V against I is
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Answer: (b) a straight line through the origin

At constant temperature V is directly proportional to I for a metallic conductor, so the V-I graph is a straight line passing through the origin.

Question 8
A cell drives a current of 0.6 A through a coil. The coil is replaced by another of three times the resistance, on the same cell. The current now is
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Answer: (a) 0.2 A

I = V/R: with V unchanged, three times the resistance gives one-third the current, 0.6 A / 3 = 0.2 A.

Question 9
A stage technician wants to dim a lamp smoothly without changing the battery. In series with the lamp he should connect
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Answer: (b) a rheostat

A rheostat changes the resistance in a circuit without changing the voltage source, so it changes the current through the lamp.

Question 10
A 2 m length of uniform nichrome wire has a resistance of 14 Ω. The resistance of a 50 cm piece cut from it is
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Answer: (a) 3.5 Ω

R ∝ l. The piece is 0.5 m / 2 m = 1/4 of the length, so R = 14 Ω / 4 = 3.5 Ω.

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