Question

Two electric bulbs marked $25W - 220V$ and $100W - 220\, V$ are connected in series to a $440\, V$ supply. Which of the bulbs will fuse ?

• A. both
• B. $100W$
• C. $25W$
• D. neither

Answer 1

Answer: (C)

$25W$

Answer 2

As $R_{1}=\frac{220}{25}\times220$ and $R_{2}=\frac{220}{100}\times220$ $R=R_{1}+R_{2}$ $=220\times220\left(\frac{1}{25}+\frac{1}{100}\right)$ $220\times220 \frac{1}{20}$ $\therefore I_{live}=\frac{440}{\frac{220\times 220}{20}}=\frac{40}{220}A$ $\therefore$ 1st bulb (25 W) will fuse only