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

Explanation

We know that `P= (V^(2))/(R)`
`:. R= (V^(2))/(P)`
Resistance of Ist lamp,
`R_(1)= (V^(2))/(P)= (220 xx 220)/(100)= 484Omega`
Resistance of 2nd lamp,
`R_(2)= (220 xx 220)/(60)= (2420)/(3)Omega`
Since, two lamps are connected in parallel, so its equivalent resistance is given by
`(1)/(R)= (1)/(R_(1))+ (1)/(R_(2))`
`= (1)/(484)+ (3)/(2420)= (8)/(2420)`
`R= (2420)/(8)Omega`
Current drawn from the line
`I= (V)/(R) (220 xx 8)/(2420)= 0.73A`