Question

Define the current sensitivity of a galvanometer. Write its S. I. unit. Figure shows two circuits each having a galvanometer and a battery of $3V$. When the galvanometers in each arrangement do not show any deflection, obtain the ratio $\frac{R_1}{R_2}$.

Answer 1

Current sensitivity of a galvanometer is defined as the deflection in galvanometer per unit current. Its SI unit is radians/ampere.


For balanced Wheatstone bridge, there will be no deflection in the galvanometer.
$\frac{4}{R_1}=\frac{6}{9}$
$R_1=\frac{4\times 9}{6}=6\Omega$


For the equivalent circuit, when the Wheatstone bridge is balanced, there will be no deflection in the galvanometer.
$\frac{12}{8}=\frac{6}{R_2}$
$R_2=\frac{6\times 8}{12}$
$=4\Omega$
$\therefore \frac{R_1}{R_2}=\frac{6}{4}=\frac{3}{2}$