Question

A galvanometer is converted into an ammeter by adding:

• A. low resistance in parallel
• B. high resistance in series
• C. low resistance in series
• D. high resistance in parallel

Hint:

A galvanometer + low resistance in parallel = Ammeter;
A galvanometer + high resistance in series = Voltmeter.

Answer 1

The Correct Option is A

To convert a galvanometer into an ammeter, a low-resistance resistor called a shunt is connected in parallel with the galvanometer coil. This arrangement allows most of the current to bypass the galvanometer, preventing it from being damaged by large currents. The shunt resistor \( R_s \) is chosen such that only a small, safe fraction of the total current passes through the galvanometer, while the remainder flows through the shunt. This enables the device to measure much higher currents than the galvanometer’s full-scale deflection current. By carefully selecting the value of \( R_s \), the ammeter can provide an accurate measurement of the total current \( I \), which is the sum of the currents through the galvanometer \( I_g \) and the shunt \( I_s \): \[ I = I_g + I_s. \] Thus, the galvanometer with a shunt resistor acts as an ammeter capable of measuring large currents safely.