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 The resistance of the
bulb is
(
)
2
2
220 V
484
100 W
V
R
=P
=
=
Ω
(b) The peak voltage of the source is
V
2
311
vm
V
=
=
(c) Since, P = I V
100 W
0