Class 10 Physics Unit-14: Current Electricity, Solved MCQs With Verified Answers. (National Book Foundation 2022 as Federal Text Book, Islamabad)

1. A current of 10 mA is flowing through a wire for 10 s. What is the amount of charge flowing through the wire?

(a) 10⁻³ C
(b) 10⁻² C
(c) 10⁻¹ C
(d) 10 C

... Answer is (c) 10⁻¹ C
`\I` = `\frac {Q}{t}` or Q = `\I` t electrons

2. 1 A current is passing through a conductor. How many electrons pass through its cross-sectional area in one second?

(a) 1.6 ｘ 10⁻¹⁹ electrons
(b) 6.25 ｘ 10⁻¹⁹ electrons
(c) 1 electron
(d) 6.25 ｘ 10¹⁸ electrons

... Answer is (d) 6.25 ｘ 10¹⁸ electrons
`\I` = `\frac {Q}{t}` or Q = `\It` = 1 A ｘ1s = 1 C and 1 C = 6.25 ｘ 10¹⁸ electrons

3. If the voltage applied to the bulb is doubled then its power becomes:

(a) doubles
(b) half
(c) 4 times
(d) one fourth

... Answer is (c) 4 times​
According to Ohm's law Voltage and current are directly related. So if the voltage is doubled the current flow will also double. As P = VI, Therefore double the current multiplied by double the voltage will 4 times (quadruple) the power.

4. Electron volt is NOT the unit of

(a) electric energy
(b) work
(c) electric potential
(d) heat energy

... Answer is (b) work
An electron volt is a unit of Energy.

5. By applying a potential difference of 10 V across a conductor, a current of 1.5 A passes through it. How much energy would be obtained from the current in 2 minutes?

(a) 18 J
(b) 180 J
(c) 18 kJ
(d) 1.8 kJ

... Answer is (d) 1.8 kJ
E = `\I`ｘVｘt

6. ohm-m is the unit of_____

(a) electric energy
(b) specific resistance
(c) electric potential
(d) heat energy

... Answer is (b) specific resistance
ohm-m is the unit of Electrical resistivity or specific resistance

7. If 4 kilo-ohm and 2 kilo-ohm resistances are connected in parallel, their equivalent resistance is: :

(a) 6 kilo-ohm
(b) 1.3 kilo-ohm
(c) 8 kilo-ohm
(d) 2 kilo-ohm

... Answer is (b) 1.3 kilo-ohm
`\frac {1}{R_{eq}}` = `\frac {1}{R_1}` + `\frac {1}{R_2}`

8. If the current through a fixed resistance is doubled then energy dissipation is:

(a) doubles
(b) half
(c) 4 times
(d) one fourth

... Answer is (c) 4 times
E = `\I^2`Rt

9. . Fuse is always connected in series with

(a) Live wire
(b) earth wire
(c) neutral wire
(d) shunt wire

... Answer is (a) Live wire
A fuse is always connected in series because. when in a short circuit high current melts the fuse, breaks down the entire circuit and the current flow stops.
 

10. With the increase in the temperature of thermistors, their resistance

(a) increases
(b) decreases
(c) remain same
(d) may increase or decrease

... Answer is (a) increases
The thermistor is a resistor whose resistance is dependent on temperature and is used as a fuse in the electric circuit.

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