question_answer

Three \[60\text{ }W,\] \[120V\]light bulbs are connected across a \[120V\] power source. If resistance of each bulb does not change with current, then find out the total power delivered to the three bulbs.

A) \[180\,W\]

B)                    \[20\,W\]

C) \[40\,W\]           

D)        \[60\,W\]

Correct Answer: C

Solution :

[c]  Here \[R=\frac{{{V}^{2}}}{P}\] Total power supplied \[=\frac{{{V}^{2}}}{3/2R}=\left( \frac{2}{3} \right)\left( \frac{{{V}^{2}}}{R} \right)=\frac{2}{3}\times 60=40W\]