Question

50 electric bulbs are connected in series across a 220 V supply and the illumination produced is $I_1$.

5 bulbs are fused. If the remaining 45 are again connected in series, the illumination produced is $I_2$. Which of the following is true?

• A. $I_1=I_2$
• B. $I_1<I_2$
• C. $I_1>I_2$
• D. It will depend on the resistance of each bulb.

Answer 1

Answer: (B)

$I_1<I_2$

Let resistance each bulb $=R_b$

Total resistance of 50 bulbs in series $=50R_b$ and total resistance of 45 bulbs in series $=45R_b$. Thus, resistance of 45 bulbs is less than of 50 bulbs.

As illumination is proportional to the heat generated, $H=\left(V^2/R\right)t$ so illumination produced, $I_1<I_2$