Q. Two point changes $+ q$ and $–q$ are held fixed at $( - d,0)$ and $(d,0)\ $respectively of a $(x,y)$ coordinate system, then
A) The electric field $\overrightarrow{E}$ at all points on the x-axis has the same direction.
B) $\overrightarrow{E}$ at all points on the $y$-axis is along $\overrightarrow{\dot{j}}\ $
C) Work has to be done in bringing a test charge from infinity to the origin.
D) The dipole moment is 2$\ qd$ directed along $\widehat{\dot{j}}\ .\ $
Explanation
(b) The two charges form an electric dipole and for this dipole any point on $y$-axis is at the equatorial line. Hence, $\overrightarrow{E}$ at all point on y-axis will be in a direction opposite to $\overrightarrow{p}$ and $\overrightarrow{p}$ is along negative $x$-axis. So $\overrightarrow{E}\ $is along positive $x\ $–axis , $ie,$ along $\widehat{\dot{i}}\ .$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.