Question

Electric bulb is used at 100w and 220v find resistance

Answer 1

p=v²/r

100=220×220/r

r=220×220/100
r=22×22=484 ohm

Answer 2

Power, P = 100 W
Voltage, V = 220 V

so, P = V*I
so, I = P/V = 100/220 = 10/22

So, R = V/I = 220*22/10
          = 484 Ohm