In DC circuits, the electric power equation can be simplified from:

p(t) = v(t) \times i(t)to the following since voltage and current do not vary with time.

P = V \times IWhere:

V = voltage drop across a load in volts.

I = current going through a load in amperes.

P = instanteous and average power absorbed in watts.

By combining the above with Ohm’s Law, power can also be expressed as the following:

\begin{aligned} P &= V \times I \\ &= (I \times R) \times I \\ &= I^2 R \end{aligned}or

\begin{aligned} P &= V \times I \\ &= V \times \frac{V}{R} \\ &= \frac{V^2}{R} \end{aligned}