Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?

Given,V=220 VPower rating of each bulb,P=10 WTotal current,It=5 ALet number of lamps in parallel ben.Let individual resistance of each lamp beR.From Joule's law of heating,P=V2/R10=2202/RR=4840 (i)R1=R2=..=Rn=R. (ii)For resistances in parallel,1Req=1R1+1R2+..+1Rn(iii)From (ii) and (iii),Req=R/n. (iv)Substituting (i) in (iv),Req=4840/n.. (v)From Ohm's Law,V=ItReq(vi)Substituting (v) in (vi),220=5×4840/nn=110