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

Explanation

Here, the voltage rating of each bulb is 220 V and the power rating of each bulb is 10W.
So, the resistance of each bulb
`R = V^2/rho = (220^2)/10 = (220 xx 220)/10 = 4840 Omega`
Now, here, V = 220 V and I = 5 A given.
So, the total resistance of the given circuit is
`R_("total") =V/I =220/5 =44 Omega`
i.e., When `44 Omega` resistance is connected with 220 V line, 5 A current would flow through the given circuit.
Now, when .n. bulbs each of resistance R, are connected in parallel, their equivalent resistance `R_("total") =R/n`
Hence, `44 =(4840)/n`
`:. n= 4840/44 =110`
Thus, 110 bulbs each of resistance 4840 `Omega` connected in parallel will result in total resistance of `44Omega` causing a current of 5 A to flow, when connected to the 220 V line.