Q. The variation of potential with distance $R$ from a fixed point is as shown below. The electric field at $R = 5m$ is
A) $2.5\ volt/m$
B) $- 2.5\ volt/m$
C) $2/5\ volt/m$
D) $- 2/5\ volt/m$
Explanation
(a) Intensity at $5m$ is same as at any point between $B$ and $C$ because the slope of $BC$ is same throughout ($i.e,$ electric field between $B$ and $C$ is uniform). Therefore electric field at $R = 5m$ is equal to the slope of line $BC$ hence by
$E = \frac{- dV}{dr};$
$E = - \frac{(0 - 5)}{6 - 4} = 2.5\frac{V}{m}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.