Question

A teacher in his physics laboratory allotted an experiment to determine the resistance $(G)$ of a galvanometer. Students took the observations for $\frac{1}{3}$ deflection in the galvanometer. Which of the below is true for measuring value of $G$ ?

• A. $\frac{1}{3}$ deflection method cannot be used for determining the resistance of the galvanometer.
• B. $\frac{1}{3}$ deflection method can be used and in this case the $G$ equals to twice the value of shunt resistance(s).
• C. $\frac{1}{3}$ deflection method can be used and in this case, the $G$ equals to three times the value of shunt resistance(s)
• D. $\frac{1}{3}$ deflection method can be used and in this case the $G$ value equals to the shunt resistance(s).

Answer 1

Answer: (B)

In galvanometer
$\Rightarrow\left( I - I _{ g }\right) S = I _{ g } G$

$\frac{I_{g}}{I}=\frac{S}{S+G}$
$\Rightarrow \frac{1}{3}=\frac{S}{S+G}$
$ \Rightarrow S+G=3 S $
$\Rightarrow G=2 S$