Q. With a potentiometer null point were obtained at $140\ cm$ and $180\ cm$ with cells of emf $1.1\ V$ and one unknown $X$ volt. Unknown emf is
A) $1.1\ V$
B) $1.8\ V$
C) $2.4\ V$
D) $1.41\ V$
Explanation
(d) $E = \frac{V}{l};E$ is constant (volt. gradient)
$\Rightarrow \frac{V_{1}}{l_{1}} = \frac{V_{2}}{l_{2}} \Rightarrow \frac{1.1}{140} = \frac{V}{180} \Rightarrow V = \frac{180 \times 1.1}{140} = 1.41\ V$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.