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

If a string of these lights consists of 12 bulbs, what is the potential difference across each bulb?

We should not get afraid if there is no number data or less number data as there is everything in the question itself, As in the question there is given that the 12 bulbs are identical and there is the input voltage of 240 V, and the bulbs are connected in series which means the current is same in each and every bulb.

Suppose that each bulb has resistance ‘R’ and ‘I’ is the current passing through each bulb,

We have to find the potential difference across each bulb, which will come out to be same because the current passing and resistance of each bulb is same, and V = I× R, so V is same which is potential difference across one bulb.

By adding the resistance of all bulbs, we get,

Potential difference across all bulbs = (current through one bulb) × (resistance of all bulbs)

Which is, 240 = I× 12R = 12 IR, = 20

Now potential difference through one bulb is,

= 20 V, which is the required potential difference across each bulb.