Q. In the following circuit, bulb rated as $1.5\ V,\ 0.45\ W.$ If bulbs glows with full intensity then what will be the equivalent resistance between $X$ and $Y$
A) $0.45\ \Omega$
B) $1\ \Omega$
C) $3\ \Omega$
D) $5\ \Omega$
Explanation
(b) When bulb glows with full intensity, then voltage across it will be $1.5\ V$ and voltage across $3\ \Omega$ resistance will be $4.5\ V$
Current through $3\ \Omega$ resistance $i = \frac{4.5}{3} = 1.5A$
Same current will flow between $X$ and $Y$
So $V_{XY} = iR_{XY} \Rightarrow 1.5 = 1.5R_{XY} \Rightarrow R_{XY} = 1\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.