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