Question
40 electric bulbs are connected in series across a $$220\,V$$ supply. After one bulb is fused the remaining 39 are connected again in series across the same supply. The illumination will be
A.
more with 40 bulbs than with 39
B.
more with 39 bulbs than with 40
C.
equal in both the cases
D.
in the ratio $${40^2}:{39^2}$$
Answer :
more with 39 bulbs than with 40
Solution :
As the voltage is same for both forty and thirty nine bulbs combination, therefore heat produced is given by $$H = \frac{{{V^2}t}}{R}$$ and $$H \propto \frac{1}{R}.$$ As equivalent resistance decreases, the combination of 39 bulbs will glow more.