Alternating Current (AC) cannot be measured by DC ammeter because:

Question

Alternating Current (AC) cannot be measured by DC ammeter because:

1. A. Alternating current cannot pass through the DC ammeter
2. B. Average value of complete cycle is zero (Correct answer)
3. C. Alternating current changes its direction
4. D. None of the above

Correct Answer

Option B — Average value of complete cycle is zero

Detailed Solution & Explanation

The correct answer is Average value of complete cycle is zero.

Key Points

• A DC ammeter responds to the average value of the current passing through it.
• Over one complete cycle, an alternating current spends equal time positive and negative, so its average value is zero.
• The moving coil therefore experiences no net deflecting torque and the instrument reads zero, regardless of how large the AC actually is.

Additional Information

• Alternating current does pass through the meter, so Option A is wrong; the problem lies in the averaging, not in conduction.
• To measure AC, use a moving-iron meter or a rectifier-type instrument, both of which respond to the RMS or rectified average value instead.