100 J of heat is produced each second in a 4 Ω resistance. Find the potential difference across the resistor.

H = 100 J, R = 4 Ω, t = 1 s, V =?

We have the current through the resistor as $\mathrm{I}=\sqrt{(\mathrm{H}/\mathrm{Rt})}$

$$\begin{gathered} \Rightarrow \mathrm{I}=\sqrt{(100/4\times 1)} \\ \Rightarrow \mathrm{I}=5\mathrm{A} \end{gathered}$$

Thus the potential difference across the resistor, V is

V = IR = 5 A × 4 Ω = 20 V.