Question

Old - fashioned serial lights were connected in a series across a 240V household line.
i) If a string of these lights consists of 12 bulbs, what is the potential difference across each bulb?
ii) If the bulbs were connected in parallel, what would be the potential difference across each bulb?

Answer 1

Given: Old - fashioned serial lights were connected in a series across a $240V$ household line.

To find: (i) the potential difference across each bulb, when a string of these lights consists of 12 bulbs

(ii) the potential difference across each bulb, when the bulbs were connected in parallel

Solution:

(i) Let $V_1$ be the potential difference across each bulb in series,

Then according to the given condition,

$12V_1=240V⟹V_1=\frac{240}{12}⟹V_1=20V$

Hence the potential difference across each bulb = $20V$ when 12 bulbs are connected in series

(ii) When the 12 bulbs are connected in parallel, the potential difference across each bulb is equal to the total voltage.

Hence the potential difference across each bulb= $240V$