Answer:
Always perpendicular to an equipotential surface
Explanation:
The space surround by a charge is called electric field. The surface where the electric potential is constant is called equipotential surface. The work done in moving a charge in electric field is given by :
[tex]W=F\times d[/tex]
Electric force is, F = qE
[tex]W=qEd\ \cos\theta[/tex]
In equipotential surface, work done by the charge is 0.
So,
[tex]0=qEd\ \cos\theta[/tex]
[tex]\theta=90^{\circ}[/tex]
Hence, the correct option is (a) "always perpendicular to an equipotential surface".