Physics - Current Electricity Question with Solution | TestHub

One of the circuits for the measurement of resistance by potentiometer is shown. The galvanometer is connected at point A and zero deflection is observed at length $\mathrm{PJ}=30\mathrm{cm}$. In second case the secondary cell is changed and the zero deflection is observed at length $\mathrm{PJ}=10\mathrm{cm}$. What is the resistance R (in ohm)? Take ${\mathrm{E}}_{\mathrm{S}}=10\mathrm{V}\&\mathrm{r}=1\Omega$ in $1^{\text{st }}$ reading and ${\mathrm{E}}_{\mathrm{S}}=5\mathrm{V}\&\mathrm{r}=2\Omega$ in $2^{\text{nd }}$ reading:-