Question

A galvanometer of resistance \(20\,\Omega\) has a current sensitivity of 5 div/mA. The instrument has 50 divisions. It can be converted into a voltmeter reading up to 25 V by connecting a resistance of

• A. \(20\,\Omega\) in parallel
• B. \(1240\,\Omega\) in series
• C. \(2480\,\Omega\) in parallel
• D. \(2480\,\Omega\) in series

Hint:

Voltmeter is always made by adding a high resistance in series.

Answer 1

The Correct Option is D

Step 1: Calculating full-scale deflection current.
\[ I_g = \frac{50}{5} = 10\,\text{mA} = 0.01\,\text{A} \]
Step 2: Total resistance required for voltmeter.
\[ R = \frac{V}{I_g} = \frac{25}{0.01} = 2500\,\Omega \]
Step 3: Series resistance required.
\[ R_s = R - G = 2500 - 20 = 2480\,\Omega \]
Step 4: Conclusion.
A resistance of \(2480\,\Omega\) in series is required.