Electric Potential: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Electric Potential. Understanding the underlying formula is key to arriving at the correct answer below:

Electric lines of force are always perpendicular to equipotential surfaces. This ensures that the component of the electric field along the equipotential surface is zero, meaning no work is done in moving a charge along it. Thus, the angle is $90^{\circ}$.