Question

In conversion of moving coil galvanometer into an ammeter of required range, the resistance of ammeter so formed is

• A. \( \frac{S + G}{SG} \)
• B. \( \frac{SG}{S - G} \)
• C. \( \frac{SG}{S + G} \)
• D. \( \frac{S - G}{SG} \)

Hint:

When converting a galvanometer to an ammeter, the shunt resistance is used in parallel to reduce the effective resistance and extend the range.

Answer 1

The Correct Option is C

Step 1: Ammeter conversion.
When converting a moving coil galvanometer into an ammeter, a shunt resistance \( S \) is added in parallel with the galvanometer to allow more current to pass through the ammeter.
Step 2: Expression for total resistance.
The total resistance of the ammeter formed is given by the formula for two parallel resistors: \[ R_{\text{total}} = \frac{SG}{S + G} \] where \( G \) is the resistance of the galvanometer and \( S \) is the shunt resistance.
Step 3: Conclusion.
The correct resistance is \( \frac{SG}{S + G} \), so the correct answer is (C).