Alternating current can not be measured by D.C. Ammeter because

Options

A. A.C. cannot pass through D.C. ammeter
B. A.C. changes direction
C. average value of current for complete cycle is zero
D. D.C. anmeter will get damaged

Explanation

To solve the question of why an alternating current (AC) cannot be measured by a direct current (DC) ammeter, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding DC Current**:
- Direct current (DC) flows in one direction only. For example, if we have a battery connected in a circuit, the current will consistently flow from the positive terminal to the negative terminal.

2. **Average Current in DC**:
- The average current for DC is calculated over time and is a constant value since it does not change direction. The average value of DC current is simply the value of the current itself.

3. **Understanding AC Current**:
- Alternating current (AC), on the other hand, changes direction periodically. In one half of the cycle, it flows in the positive direction, and in the other half, it flows in the negative direction.

4. **Average Current in AC**:
- When calculating the average current for AC over a complete cycle, the positive and negative halves cancel each other out. Therefore, the average value of AC current over one complete cycle is zero.

5. **DC Ammeter Functionality**:
- A DC ammeter is designed to measure the average current. Since it measures the average current as a non-zero value, it cannot accurately measure the AC current, which has an average value of zero.

6. **Conclusion**:
- Since the average value of AC current is zero, a DC ammeter will read zero when attempting to measure AC current. Thus, a DC ammeter cannot be used to measure AC.

### Final Answer:
Alternating current cannot be measured by a DC ammeter because the average value of the alternating current over a complete cycle is zero, leading the DC ammeter to read zero.