MCQs on Electric Circuits

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01․ A 100 μF capacitor supplied from 3 V source with a frequency of 50 Hz. The capacitive reactance is
63.68 Ω.
15.92 Ω.
31.84 Ω.
7.96 Ω.

The capacitive reactance can be expressed as \

02․ A capacitor
passes AC but blocks DC.
passes DC but blocks AC.
passes both AC and DC.
blocks both AC and DC.

The impedance of capacitor can be expressed as \ Hence, impedance of capacitor is inversely proportional to the supply frequency(f). In ac frequency has non - zero finite value, so impedance will have finite value but in DC f = 0, so impedance will have infinitely large value. Thus a capacitor blocks DC but passes AC.

03․ Which of the following carbon coded resistor has value of 10k ohm with 20% tolerance?
Brown, black, orange and no tolerance band.
Yellow, violet, yellow and silver stripes.
Orange, orange, black and gold stripes.
Red, red, green and silver stripes.

For 10k Ohm, the first digit is 1 which corresponds to brown, the second digit is 0 which corresponds to black and the multiplier is 1000 which corresponds to orange. Finally the tolerance is 20% which corresponds to no strips.

04․ Which of the following are typical resistance and power-dissipation values for a carbon-composition resistor?
10000 ohms, 10 W.
1000000 ohms, 1 W.
5000 ohms, 100W.
10 ohm, 50 W.

Carbon composition resistors consist of a solid cylindrical resistive element with embedded wire leads or metal end caps to which the lead wires are attached. Hence, the wire leads might have a range of mega ohms and the size is small which leads to carry less power dissipation. So, 1000000 ohms, 1 Watt is the normal rating of carbon composition resistor.

05․ A current of 1 mA flows through a 1M ohm, 2 W carbon resistor. The power dissipated as heat in the resistor will be
2 W.
1 W.
0.5 W.
none of the above.

The power dissipated across the resistance is P = I2R = (1 × 10-3) 2 × 1 × 106 = 1 × 10-6 × 1 × 106 = 1 Watt. The power dissipated as heat in the resistor is 1 Watt.

06․ Three 60 W bulbs are in parallel across the 60 V power line. If one bulb burns open
there will be heavy current in the main line.
rest of two bulbs will not light.
all three bulbs will light.
the other two bulbs will light.

First of all, we need to know one thing that the voltage is same in parallel circuit. So, if any one of the load is disconnected or failed, then the remaining loads are still connected with the power supply. So, that loads can work. This same principle can apply in this question also. Hence, the remaining other two bulbs can glow.

07․ The filament of an electric bulb is made of

Tungsten has the highest melting point than all other metals. That is why we used to make the filament by using tungsten metal than other metals.

08․ Which of the following quantities remain the same in all parts of a parallel circuit

A sample resistance based parallel circuit is given below. If we apply a voltage to this circuit, the current can be divided into two paths. Current can change with respect to the change in resistance. Due to this, power can also change. Hence, in parallel circuit, the voltage will be same at all the conditions.

09․ A 3Ω resistor having 2A current will dissipate the power of
2 W.
4 W.
12 W.
8 W.

The expression for power dissipation is P = I2R. Hence, P = 22 × 3 = 4 × 3 = 12 W.

10․ Two resistances R1 and R2 are connected in series across the voltage source where R1 > R2. The largest drop will be across
either R1 or R2.
none of them.

In series connection, the current flow through the two resistors is same. We know that the voltage drop by the resistor V = IR. Hence, the drop by the resistance R1 is V1 = IR1 and the drop by the resistance R2 is V2 = IR2. If the resistance R1 > R2, then the largest drop should be across the resistance R1.