1. The main advantage of alternating current (AC) over direct current (DC) is that:
a) AC is safer than DC
b) AC can be easily converted to different voltages using transformers
c) AC is more economical
d) AC can be generated easily
Answer:
b) AC can be easily converted to different voltages using transformers
Explanation:
Transformers work on the principle of electromagnetic induction, which is only possible with AC.
2. The frequency of the domestic power supply in most countries is:
a) 30 Hz
b) 50 Hz
c) 60 Hz
d) 100 Hz
Answer:
b) 50 Hz
Explanation:
Most countries, especially in Europe and Asia, use a 50 Hz frequency for their domestic power supply.
3. In an AC circuit, the value which represents its maximum voltage is called:
a) Peak voltage
b) Root mean square voltage
c) Average voltage
d) Instantaneous voltage
Answer:
a) Peak voltage
Explanation:
Peak voltage represents the maximum voltage value in an AC circuit.
4. Which of the following devices works on the principle of mutual induction?
a) DC motor
b) Transformer
c) Diode
d) Resistor
Answer:
b) Transformer
Explanation:
Transformers work based on the principle of mutual induction between two or more coils.
5. The current which changes its direction periodically is:
a) Direct Current
b) Alternating Current
c) Instantaneous Current
d) Average Current
Answer:
b) Alternating Current
Explanation:
Alternating Current (AC) changes its direction and magnitude periodically.
6. In a purely resistive AC circuit, the current:
a) Leads the voltage by 90°
b) Lags behind the voltage by 90°
c) Is in phase with the voltage
d) Can be any phase with respect to the voltage
Answer:
c) Is in phase with the voltage
Explanation:
In a purely resistive circuit, voltage and current are in phase with each other.
7. In a purely capacitive AC circuit, the current:
a) Leads the voltage by 90°
b) Lags behind the voltage by 90°
c) Is in phase with the voltage
d) Is independent of the voltage
Answer:
a) Leads the voltage by 90°
Explanation:
In a purely capacitive circuit, current leads the voltage by 90°.
8. The power factor of a purely resistive AC circuit is:
a) 0
b) 0.5
c) 1
d) Undefined
Answer:
c) 1
Explanation:
Power factor is the cosine of the phase angle. For a purely resistive circuit, the phase angle is 0°, making the power factor 1.
9. The impedance of an AC circuit is the:
a) Resistance in the circuit
b) Total opposition to the flow of alternating current
c) Reactive power in the circuit
d) Rate at which work is done
Answer:
b) Total opposition to the flow of alternating current
Explanation:
Impedance combines both resistance and reactance, offering total opposition to AC.
10. A choke is used in a tube light to:
a) Decrease the current
b) Increase the current
c) Increase the voltage momentarily
d) Reduce the voltage momentarily
Answer:
c) Increase the voltage momentarily
Explanation:
The choke, being an inductor, provides a large inductive reactance that momentarily increases the voltage to start the discharge in the tube.
11. The reactance offered by a capacitor to alternating current is:
a) Directly proportional to the frequency and the capacitance
b) Inversely proportional to the frequency and the capacitance
c) Directly proportional to the frequency and inversely proportional to the capacitance
d) Inversely proportional to the frequency and directly proportional to the capacitance
Answer:
c) Directly proportional to the frequency and inversely proportional to the capacitance
Explanation:
Capacitive reactance, Xc = 1/(2πfC), where f is frequency and C is capacitance.
12. Which device converts AC into DC?
a) Transformer
b) Rectifier
c) Inverter
d) Transistor
Answer:
b) Rectifier
Explanation:
A rectifier is an electrical device that converts alternating current (AC) to direct current (DC).
13. The power consumed in a purely capacitive circuit is:
a) Maximum
b) Minimum
c) Zero
d) Equal to the power in a purely resistive circuit
Answer:
c) Zero
Explanation:
In a purely capacitive circuit, the power factor is zero, hence power consumed is zero.
14. The symbol '~' represents:
a) Direct Current
b) Alternating Current
c) High Voltage
d) Low Voltage
Answer:
b) Alternating Current
Explanation:
The '~' symbol is used to represent alternating current (AC).
15. In a series LCR circuit at resonance, the:
a) Current is minimum
b) Voltage is minimum
c) Current is maximum
d) Resistance is maximum
Answer:
c) Current is maximum
Explanation:
At resonance in a series LCR circuit, the inductive reactance equals capacitive reactance, making impedance minimum and current maximum.