Old – fashioned serial lights were connected in a series across a 240V household line.

If the bulbs were connected in parallel, what would be the potential difference across each bulb?

We know that potential difference across each bulb is same when they are connected in parallel and in this case the bulbs too are identical that is they have same resistance and so the current will be divided in same proportion in each branch (to each resistor).

The conditions are same as in the previous case,

Effective resistance of the network is,

We get,

R_t , Let the current flowing in circuit is I,

By Ohm’s law, 240 = I× R_t ,

As current through circuit is I, so current through each bulb will be , because there are 12 bulbs through which current I is flowing so through one bulb the current will be ,

By Ohm’s law, , which is equal to 240 V.

Hence now we know the rule works always.