Physics - Current Electricity Question with Solution | TestHub

Given: Initial number of cells $\left(n_1\right)=10$; Potential of each cell $=E$; Internal resistance of each cell $=r$ and final number of cells $\left(n_2\right)=3$. We know from the Ohm's law, total voltage of ten cells $=10\times E=10E$ and total resistance in ten cells $=10\times r=10r$. Therefore current in the circuit, $I=\frac{10E}{10r}=\frac{E}{r}$ or potential difference across three cells $=I\times 3r=\frac{E}{r}\times 3r=3E$. (Since the voltmeter is ideal, therefore it will $\mathrm{read}3E)$.