Q. A cell in secondary circuit gives null deflection for $2.5m$ length of potentiometer having $10m$ length of wire. If the length of the potentiometer wire is increased by $1\ m$ without changing the cell in the primary, the position of the null point now is
A) $3.5\ m$
B) $3\ m$
C) $2.75\ m$
D) $2.0\ m$
Explanation
(c) $L \propto l$
$\frac{L_{1}}{L_{2}} = \frac{l_{1}}{l_{2}}$
$\frac{10}{11} = \frac{2.5}{l_{2}}$
$10l_{2} = 2.5 \times 11$
$l_{2} = \frac{2.5 \times 11}{10} = 2.75M$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.