Electric field in a region is $\vec{E} = 3\hat{j}$ N/C. Equipotential surfaces are parallel to

Solution:

Equipotential surfaces are always perpendicular to the electric field lines. The given electric field is $\vec{E} = 3\hat{j}$ N/C, which is directed along the positive y-axis. Therefore, the equipotential surfaces must be planes perpendicular to the y-axis. A plane perpendicular to the y-axis is parallel to the xz plane. Thus, the equipotential surfaces are parallel to the xz plane.