Question

A galvanometer of 100 resistance gives full scale deflection with 0.01A current. How much resistance should be connected to convert it into an ammeter of range 10A?

• A. $0.1$ in parallel
• B. $0.1$ in series
• C. $0.2$ in parallel
• D. $0.2$ in series

Answer 1

The correct option is A $0.1$ in parallel

Given: A galvanometer of $100$ resistance gives full scale deflection with $0.01A$ current

To find the resistance that should be connected convert it into an ammeter of range $10A$

Solution:

Galvanometer is a very sensitive instrument therefore it cannot measure heavy currents. In order to convert a Galvanometer into an Ammeter, a very low shunt resistance is connected in parallel to Galvanometer. Value of shunt is so adjusted that most of the current passes through the shunt.

If resistance of galvanometer is $R_g$ and it gives full-scale deflection when current $I_g$ is passed through it. Then,

$V=I_g{R}_g⟹V=0.01A\times 100\Omega ⟹V=1V$

Let a shunt of resistance ($R_s$) is connected in parallel to galvanometer. If total current through the circuit is $I$.

$I=10A=I_s+I_g$

$V=I_s{R}_s=(I-I_g)R_s$

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

$(10-0.01)R_s=100\times 0.01⟹R_s=0.1\Omega$

is the resistance that should be connected in parallel to convert it into an ammeter of range $10A$