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

Given: Heat produced, H = 196 J, R = 4 Ω, t = 1 s, V =?

According to joule's law of heating:

$\mathrm{H}= {\mathrm{I}}^2\mathrm{Rt}$

$\therefore$ The current through the resistor will be:

$\mathrm{I}=\sqrt{\mathrm{H}/(\mathrm{R}\times \mathrm{t})}$
$\mathrm{I}=\sqrt{196/(4\times 1)}$
$\mathrm{I}=7 \mathrm{A}$

The potential difference across the resistor will be:

V = IR

V = 7 A × 4 Ω = 28 V.