# What are Equipotential Lines or Equipotential Surfaces?

## Answer #1

Level 2 (without higher mathematics)

Answered by Alexander Fufaev

An **equipotential line** (or in 3d: **equipotential surface**), is the set of all points in space that have *the same potential* \(\varphi\). A potential \(\varphi\) is *potential energy per charge*.

When a particle moves on such an equipotential line, its potential energy does not change. In other words, the particle on an equipotential line is neither accelerated nor decelerated and it can be moved on the equipotential line without losing or gaining energy.