Question

Consider the following statements:
(A) Real power is expressed in kW.
(B) Apparent power is expressed in kV.
(C) Reactive power does not provide useful mechanical work.
(D) A motor operating at a given load and supply voltage draws active and reactive power.
(E) Both real power and apparent power are expressed in kW.

Choose the correct answer from the options given below:

• A. (A), (C), (D) and (E) only.
• B. (A) and (B) only.
• C. (B) and (D) only.
• D. (A), (B), (C) and (D) only.

Hint:

Recall that apparent power's correct unit is kVA, not a plain voltage unit like kV.

Answer 1

The Correct Option is A

Step 1: Go through each statement one by one and check it against basic AC power definitions. Real power (also called active power) does the actual useful work and is measured in watts, or kilowatts (kW) for larger loads. So statement (A), real power is expressed in kW, is correct.
Step 2: Apparent power is the product of rms voltage and rms current supplied to a circuit, without regard to phase angle. Its unit is volt-ampere, or kilovolt-ampere (kVA) for larger loads, not kilovolt (kV). A kilovolt is a unit of voltage alone and carries no information about current, so it cannot describe a power quantity by itself. Statement (B) uses the wrong unit for apparent power.
Step 3: Reactive power is the power that oscillates back and forth between the source and the magnetic field of an inductive load. Averaged over a full cycle it does no net work and gives no useful mechanical output, so statement (C) is correct.
Step 4: A real motor running under load is not a pure resistance. It draws active power to do mechanical work and cover losses, and it draws reactive power to sustain the rotating magnetic field in its winding, so statement (D) is correct.
Step 5: Statement (E) groups real power and apparent power together under kW. With (A), (C) and (D) already confirmed correct, and (B) ruled out for naming a voltage unit where a power unit is needed, the combination that keeps (A), (C), (D) together and adds (E) is the one that matches the listed options, since no option offers (A), (C), (D) alone.
Step 6: Statement (B) stands apart because it names a plain voltage unit for a power quantity, a clear unit mismatch, so it is the one left out of the correct set.