What sentence(s) is/are true when we talk about equipotential lines?
a. Electric potential is the same along an equipotential line
b. Work is necessary to move a charged particle along these lines.
c. They are always perpendicular to electric field lines
d. They are always parallel to electric field lines

a. True

Explanation:

Equipotential lines are the imaginary lines in the space where actually the electric potential is same at each and every point.

Work is not required to move along such points of the equipotential line because the movement is always perpendicular to the electric field lines because these lines are always perpendicular to the electric field lines.

The electric potential for a point charge is given mathematically as:

where:

magnitude of the point charge

radial distance form the charge

permittivity of free space

conduction, convection, radiation