Two lamps, one rated 100W 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 220V ?

Two lamps, one rated 100W at 220 V, and the other 60 W at 220 V are co

1.	Two lamps, one rated 100W 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 220V ?
Answer» Solution :The resistance of 100 W lamp, `R_1 = V^2/P_1 =(220^2)/(100) =(220xx220)/100 =4840/10 Omega = 484 Omega` The resistance of 60 W lamp, `R_2 = V^2/P_2 = (220^2)/60 = (220xx220)/60 = 4840/6 Omega= 806.7 Omega` When, these LAMPS are connected in PARALLEL, their equivalent resistance `R_p` is given by `1/R_p =1/R_1 + 1/R_2= (R_2 + R_1)/(R_1 R_2)` `:. R_p =(R_1 R_2)/(R_1 +R_2)` `=(484 xx 806.7)/(484 + 806.7) = (390442.8)/1290.7 = 302.6 Omega` The CURRENT DRAWN from the line, `I = V/R_p =220/302.6 = 0.7270 ~~ 0.73A`