Can moving coil galvanometer be used to detect an a.c. in a circuit? Give reason.

Options

A. The coil bends easily
B. The coil heats up too much
C. Sparks can be produced
D. The net magnetic field produced is zero

Answer

To determine whether a moving coil galvanometer can be used to detect alternating current (AC) in a circuit, we need to analyze how the galvanometer operates and the nature of AC.

### Step-by-Step Solution:

1. **Understanding the Moving Coil Galvanometer**:
- A moving coil galvanometer operates based on the interaction between a magnetic field and a current-carrying coil. When current flows through the coil, it experiences a torque due to the magnetic field, causing the coil to rotate and move the pointer on the scale.

2. **Nature of Alternating Current (AC)**:
- AC current periodically reverses direction. For example, in a typical AC circuit, the current flows in one direction for half of the cycle (T/2) and then reverses for the other half (T/2). This means that the current alternates between positive and negative values.

3. **Effect of AC on the Galvanometer**:
- When AC flows through the galvanometer, during the positive half of the cycle, the coil will experience a torque in one direction, causing the pointer to deflect in that direction. During the negative half of the cycle, the torque will reverse, causing the pointer to deflect in the opposite direction.

4. **Average Current Calculation**:
- Over one complete cycle of AC, the positive and negative deflections will cancel each other out. Since the galvanometer measures the average current, and the average of a sinusoidal AC current over one complete cycle is zero, the galvanometer will not show any deflection.

5. **Conclusion**:
- Therefore, a moving coil galvanometer cannot be used to detect AC current in a circuit because the net magnetic field produced by the alternating current averages to zero over a complete cycle. The pointer will not indicate any current since the average deflection is zero.

### Final Answer:
No, a moving coil galvanometer cannot be used to detect AC in a circuit because the average current over a complete cycle of AC is zero, resulting in no net deflection of the pointer.

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