Question

What is current sensitivity of a galvanometer? Show how the current sensitivity of a galvanometer may be increased. Increasing the current sensitivity of a galvanometer may not necessarily increase its voltage sensitivity. Explain.

Hint:

The current sensitivity can be increased by increasing the number of turns, the area of the coil, or decreasing the torsional constant. However, increasing the current sensitivity may not always increase voltage sensitivity.

Answer 1

The current sensitivity of a galvanometer is defined as the deflection produced per unit current passing through it. It is given by the formula: \[ I_s = \frac{\theta}{I} = \frac{NBA}{K}, \] where \( \theta \) is the angular deflection, \( I \) is the current, \( N \) is the number of turns of the coil, \( B \) is the magnetic field strength, \( A \) is the area of the coil, and \( K \) is the torsional constant. The current sensitivity can be increased by: (A) Increasing the number of turns in the coil. (B) Increasing the area of the coil in the magnetic field. (C) Decreasing the torsional constant \( K \) (which means making the suspension more flexible). Increasing the current sensitivity by changing the coil's properties may also affect the resistance of the galvanometer, which in turn can alter its voltage sensitivity. As the current sensitivity increases, the voltage sensitivity may decrease because the resistance increases, which can reduce the voltage required for full-scale deflection. The current sensitivity is directly proportional to the number of turns and the area of the coil, but increasing the current sensitivity does not necessarily lead to an increase in voltage sensitivity. Voltage sensitivity is related to the resistance of the galvanometer, and increasing the number of turns to increase current sensitivity will also increase the resistance, thereby decreasing the voltage sensitivity.