Question

A galvanometer of resistance $100\Omega$ gives full scale deflection at $10mA$ current. What should be the value of shunt so that it can measure a current of $100mA$?

• A. $11.11\Omega$
• B. $1.1\Omega$
• C. $9.9\Omega$
• D. $4.4\Omega$

Answer 1

The correct option is A $11.11\Omega$

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,

$V=I_g{R}_g$

$V=100mA\times 100\Omega$

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

$I=10A=I_s+I_g$

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

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

$(10-{10}^{-3})R_s=100\times {10}^{-3}$

$R_s=11.11\Omega$