Question

A galvanometer coil has a resistance of $50\Omega$ and the meter shows full scale deflection for a current of $5mA$. This galvanometer is converted into voltmeter of range $0-20V$ by connecting

• A. $3950\Omega$ in series with galvanometer
• B. $4050\Omega$ in series with galvanometer
• C. $3950\Omega$ in parallel with galvanometer
• D. $4050\Omega$ in parallel with galvanometer

Answer 1

The correct option is A $3950\Omega$ in series with galvanometer

Given : $R_G=50\Omega$ $I_g=5mA=0.005A$ $V=20$ volts

A galvanometer is converted into a voltmeter by connecting a resistor in series with resistance of galvanometer.

Let the resistor to be connected in series with $R_G$ be $R$.

$\therefore$ $V=I_g(R_G+R)$

Or $20=0.005(50+R)$

$⟹$ $R=4000-50=3950\Omega$