Question

A light bulb is rated 100 W for 220 V ac supply of 50 Hz. Calculate

(i) The resistance of the bulb;

(ii) The rms current through the bulb.

Answer 1

P = 100 W V_rms = 220 V

(a) Resistance, R

`=V_(rms)^2/P = (220 xx 220)/100 Ω =484Omega`

(b) P = I_rms V_rms

`I_(rmo) =P/V_(rms) = (100W)/(220V)` = 0.45A