Q.
Figure shown three similar lamps $A,B\ and\ C$ connected across a power supply. If the lamp $C$ fuses, how will the light emitted by $A$ and $B$ change?
A) No change
B) Brilliance of $A\ $decreases and that of $B$ increases
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C) Brilliance of both $A$ and $B\ $increases
D) Brilliance of both $A$ and $B$ decreases
Explanation
(b) Let $R$ be the resistance of each lamp and $V$ be the voltage supplied to the circuit. Current in the circuit is
$I_{1} =$ $\frac{V}{R + \frac{R \times R}{R + R}} = \frac{2V}{3R}$
Current flowing through $B\ or\ C$,
$I_{2} = \frac{I_{1}}{2} = \frac{1}{2}\left( \frac{2V}{3R} \right) = \frac{V}{3R}$
When $C$ is fused, the whole current flows through $A$ and $B$.
Then , $I_{2}^{'} = V$/2$R$
So current through $A$ decreases and current through $B$ increases. Therefore brilliance of $A$ decreases and that of $B$ increase.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.