Question

A galvanometer of resistor 10 ohms gives a full scale deflection when a current of 50amphere flow through it.

How can it be converted to an ammeter to measure a current of 5Amphere?

How can it be converted to a voltmeter to measure a voltage of 3volts?

Answer 1

For the ammeter the parallel shunt resistance is:

$$R_S=\frac{I_g}{I-I_g}R_g=\frac{5}{50-5}10=1.11\Omega.$$

For the voltmeter the series resistance to be added is

$$R_S=R_g\bigg(\frac{V}{V_V}-1\bigg)=10\bigg(\frac{10·50}{3}-1\bigg)=1657\Omega.$$