Question

A galvanometer coil has a resistance of $150$ gives full scale deflection for a current of $4mA$. To convert it to an ammeter of range $0$ to $6A$

• A. $10m$ resistance is to be connected in parallel to the galvanometer
• B. $10m$ resistance is to be connected in series with the galvanometer
• C. $0.1$ resistance is to be connected in parallel to the galvanometer
• D. $0.1$ resistance is to be connected in series with the galvanometer

Answer 1

The correct option is C $0.1$ resistance is to be connected in parallel to the galvanometer

Galvanometer resistance $R_g=150$

Current flowing through $R_g$, $I_g=4mA=0.004A$

Let a shunt resistance $R_s$ is connected in parallel to $R_g$ to convert it into an ammeter.

Using $(I-I_g)R_s=I_g{R}_g$

$\therefore$ $(6-0.004)R_s=0.004\times 150$

Or $6\times R_s=0.6$

$⟹$ $R_s=0.1$

Hence $0.1$ resistance must be connected in parallel to the galvanometer so as to convert it into an ammeter.