Data: R = 8 Ω, L = 8 m, E = 2 V, K = 1 µV/mm

= 1 × \(\frac{10^{-6} \mathrm{~V}}{10^{-3} \mathrm{~m}}\) = 10^{-3} \(\frac{\mathrm{V}}{\mathrm{m}}\)

K = \(\frac{V}{L}=\frac{E R}{\left(R+R_{\mathrm{B}}\right) L^{\prime}}\) where R_{B} is the resistance in the box.

∴ 10^{-3} = \(\frac{2 \times 8}{\left(8+R_{B}\right) 8}\)

∴ 8 + R_{B} = \(\frac{2}{10^{-3}}\)

= 2 × 10^{3}

∴ R_{B} = 2000 – 8

= 1992 Ω