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  Solved  Paper-2012

A) both                                        

B) 100W

C) 25W                                         

D) neither 

Correct Answer: C

Solution :

               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