Answer :

The rate at which energy consumed in per unit time in any electric circuit is defined as electric power and it's s.i. unit is watt.

Electric power (p) = \( \frac{work done (w)}{time (t)} \)

[ Work in electric circuit is volt × charge ]

\( \implies \) P = vq/t

\( \because i = \frac{q}{t} \)

\( \implies \) P = vi

So, power ( p ) = volt (v)× current (I)

From ohm's law \( v = i*r \)

\( \implies i = \frac{v}{r} \)
using the above value of I in equation \( p = v*i \) we get

\( \implies p = \frac{v^2}{r} \)