Q. Point charge $q$ moves from point $P$ to point $S$ along the path $PQRS$ (figure shown) in a uniform electric field $E$ pointing coparallel to the positive direction of the $X$-axis. The coordinates of the points $P,Q,R$ and $S$ are $(a,b,0)(2a,0,0)(a, - b,0)$ and $(0,0,0)$ respectively. The work done by the field in the above process is given by the expression
A) $qEa$
B) $- qEa$
C) $qEa\sqrt{2}$
D) $qE\sqrt{\lbrack(2a)^{2} + b^{2}\rbrack}$
Explanation
(b) As electric field is a conservative field
Hence the work done does not depend on path
$\therefore W_{PQRS} = W_{POS} = W_{PO} + W_{OS}$
$= Fb\cos 90^{o} + Fa\cos 180^{o} = 0 + qEa( - 1) = - qEa$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.