Q. If a $30\ V,\ 90\ W$ bulb is to be worked on a $120\ V$ 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) $40\ ohm$
Explanation
(c) Suppose resistance $R$ is corrected in series with bulb
Current through the bulb$\ i = \frac{90}{30} = 3\ A$
Hence for resistance $V = iR \Rightarrow 90 = 3 \times R \Rightarrow R = 30\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.