Question

A galvanometer having 30 divisions has a current sensitivity of \(0.0625 \, \frac{\text{div}}{\mu\text{A}}\). If it is converted into a voltmeter to read a maximum of 6 V, then the resistance of that voltmeter is:

• A. \( 7.5 \, \text{k}\Omega \)
• B. \( 12.5 \, \text{k}\Omega \)
• C. \( 6 \, \text{k}\Omega \)
• D. \( 5 \, \text{k}\Omega \)

Hint:

To convert a galvanometer to a voltmeter, calculate the full-scale deflection current using sensitivity and multiply it with the desired voltage range to get the series resistance.

Answer 1

The Correct Option is B

Step 1: Total current for full scale deflection
Given:
Current sensitivity \( S = 0.0625 \, \frac{\text{div}}{\mu\text{A}} \)
Number of divisions \( n = 30 \)
\[ I = \frac{n}{S} = \frac{30}{0.0625} = 480 \, \mu\text{A} \] Step 2: Resistance needed for voltmeter to show 6 V
Using Ohm’s law: \[ V = IR \Rightarrow R = \frac{V}{I} = \frac{6 \, \text{V}}{480 \times 10^{-6} \, \text{A}} = 12500 \, \Omega = 12.5 \, \text{k}\Omega \]