Mdcat, NEET, PMC, Unacademy

MDCAT 2025 – Alternating Current
Past + Expected MCQs with Short Explanations
1. The alternating current changes its direction:
A) Once in a cycle B) Twice in a cycle C) Thrice D) Four times
Answer: B – It reverses direction twice per cycle.
2. The SI unit of frequency of AC is:
A) Ohm B) Hertz C) Volt D) Ampere
Answer: B – Frequency is measured in Hertz (Hz).
3. The time period of 50 Hz AC is:
A) 0.02 s B) 0.2 s C) 2 s D) 0.002 s
Answer: A – T = 1/f = 1/50 = 0.02 s.
4. The RMS value of AC is related to peak value (I■) by:
A) I■/2 B) I■/√2 C) 2I■ D) √2I■
Answer: B – Irms = I■ / √2.
5. Power factor of a purely resistive circuit is:
A) 0 B) 0.5 C) 1 D) -1
Answer: C – In resistive circuit, voltage and current are in phase.
6. The device used to convert AC to DC is:
A) Rectifier B) Transformer C) Amplifier D) Motor
Answer: A – Rectifier converts AC into DC.
7. Transformer works on the principle of:
A) Electrolysis B) Mutual induction C) Self induction D) Radiation
Answer: B – It operates on mutual induction between coils.
8. In a transformer, the power ideally remains:
A) Constant B) Doubled C) Zero D) Halved
Answer: A – In ideal transformer, input power = output power.
9. The average value of AC over one complete cycle is:
A) Zero B) Maximum C) Minimum D) Constant
Answer: A – Positive and negative halves cancel each other.
10. The frequency of AC used in Pakistan is:
A) 60 Hz B) 55 Hz C) 50 Hz D) 45 Hz
Answer: C – The standard supply frequency is 50 Hz.
11. When current lags behind voltage in a circuit, it is mainly due to:

, A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
12. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
13. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
14. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
15. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
16. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
17. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
18. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
19. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
20. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
21. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.
22. When current lags behind voltage in a circuit, it is mainly due to:
A) Inductance B) Capacitance C) Resistance D) Power loss
Answer: A – Inductive circuits cause lagging current phase.