question_answer

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?            [AIEEE 2012]

A) both     

B) 100W

C) 25W

D) neither 

Correct Answer: C

Solution :

[c]

As \[{{R}_{1}}=\frac{220}{25}\times 200\] and \[{{R}_{2}}=\frac{220}{100}\times 220\]

\[R={{R}_{1}}+{{R}_{2}}\]

\[=220\times 220\left( \frac{1}{25}+\frac{1}{100} \right)\]

\[=220\times 220\frac{1}{20}\]

\[\therefore \,{{I}_{live}}=\frac{440}{\frac{220\times 220}{20}}=\frac{40}{220}A\]

\[\therefore \] 1st bulb (25 W) will fuse only