Question

derive the expression for power P consumed by a device having resistance R and potential difference V

Answer 1

$p = \frac{ {v}^{2} }{r}$

is the required relation

Answer 2

Amount of work done in carrying chargeQ through the P.D.=V IS ,

W=QV

Q=It therefore , W=VIt

P=VIt/t=VI

P=VI =V(V/R)

P=V^2 /R

So, P=VI=I^2R=V^2/R