Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Explanation

Resistance of the first lamp = R
Resistance of second lamp = `R_(2)`
`R=V^(2)/P`
`R_(1)=(220xx220)/100=484Omega`
`R_(2)=(220xx220)/60=2420/3Omega`
They are connected in parallel
`1/R=1/R_(1)=1/R_(2)=1/484+3/2420`
`R=(484xx2420)/(3(484+2420/3))=605/3Omega`
Therefore `I=V/R=(220xx2)/605=8/11A`
I = 0.727 A.