question_answer

If a 30 V, 90 W bulb is to be worked on a 120 line, a resistance of how many ohms should be connected in series with the bulb?

A) 10 ohm            

B) 20 ohm

C) 30 ohm            

D) 40 ohm

Correct Answer: C

Solution :

Suppose resistance R is corrected in series with bulb. Current through the bulb \[i=\frac{90}{30}=3\,A\] Hence for resistance \[\operatorname{V}= iR\] \[\Rightarrow \,\,\,\,\,90 = 3 \,\times \,\,R\] \[\Rightarrow \,\,\,\,\,R=30\,\,\Omega \]