Question

A galvanometer has resistance of 100 $\Omega$ and a current of 10 mA produces full scale deflection in it. The resistance to be connected to it in series, to get a voltmeter of range 50 volt is

• A. 4900 $\Omega$
• B. 4000 $\Omega$
• C. 4600 $\Omega$
• D. 3900 $\Omega$

Answer 1

Answer: (A)

4900 $\Omega$

Answer 2

Full-scale deflection current, $I_{fs} = 10\,\text{mA} = 0.01\,\text{A}$

Voltage drop across the galvanometer, $V_g = I_{fs} \times R_g = 0.01 \times 100 = 1\,\text{V}$

Required total resistance for 50 V:

$$R_{\text{total}} = \frac{50}{0.01} = 5000\,\Omega$$

Additional series resistance to be connected:

$$R_s = R_{\text{total}} - R_g = 5000 - 100 = 4900\,\Omega$$