Question

The circuit shownin Fig. `7.33` contains a battery , a rheostat , and two identical lamps. What will happen to the brightness of the lamps if the resistance of the rheostat is increased?

A. Less brighter Brighter
B. Less brighter Loss brighter
C. Brighter Less brighter
D. No change Brighter

Answer 1

Correct Answer - A
(a) Consider two extreme cases. (i) When the resistance of the rheostat is zero, the current through `Q` is zero since `Q` is short-circuited. The circuit is then essentially a battery in series with lamp `P`. (ii) When the resesitance of the rhostat is very large, amost no current flows throuh it. So, the currents through `P` and `Q` are almost equal. The current is essentially a battery in series with lamp `P` and `Q`