As the switch $S$ is closed in the circuit shown in figure, the current passing through it is:

Current through wire $XY$ of circuit shown is

The current in resistance $R_3$ in the given circuit is:

Two batteries of emf ${\epsilon }_1$ and ${\epsilon }_2\left({\epsilon }_2>{\epsilon }_1\right)$ and internal resistances $r_1$ and $r_2$ respectively are connected in parallel as shown in figure.

A resistance $R$ is to be measured using a meter bridge, student chooses the standard resistance $S$ to be $100 \mathrm{\Omega }$. He finds the null point at $l_1=2.9 \mathrm{cm}$. He is told to attempt to improve the accuracy.

Which of the following is a useful way?