question_answer

Electric bulb 50 W-100 V glowing at full power are to be used in parallel with battery 120 V, 10 W. Maximum number of bulbs that can be connected so that they glow in full power is                                    [CPMT 2002]

A)            2    

B)            8

C)            4    

D)            6

Correct Answer: C

Solution :

                   When each bulb is glowing at full power, Current from each bulb \[=i'=\frac{50}{100}=\frac{1}{2}A\] So main current \[i=\frac{n}{2}A\]            Also \[E=V+ir\] Þ \[120=100+\left( \frac{n}{2} \right)\times 10\Rightarrow n=4\]