Question

Two lamps rating 100w at 220v ,and the other 60w at 220v, are connected in paralell to electric main supply ,what is the current drwan from the line if the supply voltage is 220v

Answer 1

let
P1 = 100W
V1 = 220V
I = P1/V1 = 100/220 = 0.45 A
V1 = I/R1
R1 = V1/I = 220/0.45 = 490 Ω

P2 = 60W
V2 = 220W
I = P2/V2 = 60/220 = 0.27 A
R2 = V2/I = 220/0.27 = 810 Ω

because they are connected parallely
1/Rp = 1/R1 + 1/R2
1/Rp = R2+R1/R1R2
Rp = R1R2/R2+R1
Rp = 490×810/490+810
Rp = 396900/1300
Rp = 305.3 Ω

V = IrR
Ir = V/R
Ir = 220/305.3
Ir = 0.72 A

Ir --> resultant current