Suppose a Current I flows through a circuit as shown in the figure. The voltage across the resistance is V . The P.D. is the work done to move a charge Q from one point to another point, between which the p.d. is applied.

W = QV

But, Q= I.t

∴ W = VIt

Another energy equation By Ohm’s Law:

V= I. R

Now, W = VIt

W = IR. It

∴ W = I^{2}Rt

We can also write the energy equation in terms of voltage , resistance and time.

W = (V / R )^{2}. Rt

∴ W = (V^{2}t) / R

∴ W = Qv = VIt = I^{2}Rt= (V^{2}t) / R