A voltmeter of resistance $\displaystyle 1000 \Omega$ can measure up to $\displaystyle 25$ V. How will you convert it so that it can read up to $\displaystyle 250$ V?

$\displaystyle I=\frac{V}{R}$ $\displaystyle =\frac{25}{1000}$ $\displaystyle =25 \times 10^{-3} \mathrm{~A}$ Resistance to be connected to voltmeter: $\displaystyle R^{\prime}=\frac{V^{\prime}}{I}-R$ $\displaystyle =\frac{250}{25 \times 10^{-3}}-1000$ $\displaystyle =9000 \Omega$ This $\displaystyle 9000 \Omega$ is in series with the voltmeter.