Question

A shunt resistance of 25 ohms is required for extending the range of an ammeter from 100 A to 500 A. The value of internal resistance of this ammeter will be:

• A. 25 ohms
• B. 50 ohms
• C. 100 ohms
• D. 1000 ohms

Hint:

When extending the range of an ammeter, the shunt resistance needed depends on the desired current range and the internal resistance of the instrument.

Answer 1

The Correct Option is C

The current through the ammeter can be extended by adding a shunt resistance in parallel. To extend the range from 100 A to 500 A, we use the formula for parallel resistances: \[ R_{\text{shunt}} = \frac{R_{\text{ammeter}}}{\text{Range Factor} - 1} \] The range factor is \( \frac{500}{100} = 5 \). Thus, the internal resistance of the ammeter is: \[ R_{\text{ammeter}} = 25 \times (5 - 1) = 100 \, \Omega \] Thus, the internal resistance is 100 ohms. Thus, the correct answer is 100 ohms.