7) can also be written as
P = V2 / R = I V    (since V = I R)
Example 7 1 A light  bulb is rated at 100W for a 220 V supply Find
(a) the resistance of the bulb; (b) the peak voltage of the source; and
(c) the rms current through the bulb Solution
(a) We are given P = 100 W and V = 220 V