Question

A galvanometer has a resistance of 30 $\Omega$ and a current of 2.0 mA gives full-scale deflection. How will you convert this galvanometer into a voltmeter of 0.2 volt range?

• A. 700 $\Omega$ resistance should be connected parallel to the galvanometer.
• B. 70 $\Omega$ resistance should be connected parallel to the galvanometer.
• C. 700 $\Omega$ resistance should be connected series to the galvanometer.
• D. 70 $\Omega$ resistance should be connected series to the galvanometer.

Answer 1

The correct option is D 70 $\Omega$ resistance should be connected series to the galvanometer.

Given resistance of Galvanometer $R_g=30\Omega$

Amount of current which show full deflection $I_g=2mA=2\times {10}^{-}3A$

Range of voltmeter=$0.2V$

To convert a galvanometer into voltmeter a resistance in series is added with the galvanometer, the resistance of the resistor is given by

$R=\frac{V}{I_g}-R_g$

$=\frac{0.2}{2\times {10}^{-}3}-30=70\Omega$