Question

A galvanometer of resistance 100 \( \Omega \) is converted into an ammeter of range (0 – 1 A) using a resistance of 0.1 \( \Omega \). The ammeter will show full-scale deflection for a current of about:

• A. 0.1 mA
• B. 1 mA
• C. 10 mA
• D. 0.1 A

Hint:

A shunt resistance is used to convert a galvanometer into an ammeter, ensuring that most of the current bypasses the sensitive galvanometer coil.

Answer 1

The Correct Option is B

Conversion of a Galvanometer to an Ammeter:
- The full-scale deflection current of the galvanometer (\( I_g \)) is given by: \[ I_g = \frac{I}{1 + \frac{R_g}{R_s}} \] where \( I \) is the total current, \( R_g = 100 \Omega \) is the galvanometer resistance, and \( R_s = 0.1 \Omega \) is the shunt resistance.
- Given that the ammeter range is 1 A, we solve for \( I_g \): \[ I_g = \frac{1}{1 + \frac{100}{0.1}} = \frac{1}{1 + 1000} = \frac{1}{1001} \] \[ I_g \approx 1 mA \] Thus, the correct answer is 1 mA.