The resistance of a moving coil galvanometer is 20Ω. It requires 0.01 A current for full scale deflection. Calculate the value of resistance required to convert it into a voltmeter of range 20 volt:

Given Data:

• Resistance of the galvanometer, R_g = 20 Ω
• Full-scale deflection current, I_g = 0.01 A
• Desired voltage range, V = 20 V

Step-by-Step Calculation

The total voltage across the galvanometer and the series resistance is given by:

V = I_g (R_g + R_s)

Rearranging for R_s (series resistance):

R_s = V / I_g - R_g

Substitute the given values:

R_s = 20 / 0.01 - 20

R_s = 2000 - 20 = 1980 Ω

Final Answer

The resistance required to convert the galvanometer into a voltmeter of range 20 volts is 1980 Ω.

Correct Option:

1980Ω