Question

Explain how moving coil galvanometer is converted into a voltmeter. Derive the necessary formula.

Answer 1

Galvanometer cannot measure high potential difference. To make it capable of doing so i.e. to convert a Galvanometer into voltmeter, a very high resistance is connected in series with the galvanometer.
Let resistance of galvanometer be G and resistance R is connected in series to it. Then combined resistance = (G + R).
If V is he potential difference to be measured and if galvanometer gives full-scale deflection, when current I passes through it.
Then, $I=\frac{V}{R+G}$
or required resistance to be connected in series is R=$\frac{V}{I}-G$