# Potential difference

Voltage between two points. A charge q moved across a voltage V gains energy qV.

Physics (university) · Part 07: Electric fields and potential · Card 8 of 10 · Last updated 2026-10-19

## Analogy

A ski lift raises skiers, a battery raises charges.

## Example

**Electron in 100 V**

W = q V
W = 1.6e-19 x 100
W = 1.6e-17 J

## In practice

An electron accelerated through 100 V gains 1.6e-17 J.

## Questions people ask

### What is an electron-volt?

An electron-volt is the energy an electron gains going through one volt: 1.6e-19 J. It is a handy unit for atoms and particles, where joules are inconveniently large. A photon of visible light carries around 2 to 3 electron-volts of energy.

### How do I find the speed of a charge accelerated through a voltage?

Set the energy gained equal to kinetic energy: qV = 1/2 m v squared. For an electron through 100 V, v = sqrt(2 x 1.6e-19 x 100 / 9.11e-31), which is about 5.9e6 m/s. For high speeds you need relativity.

## Related concepts

- [Electric charge](https://studyvisually.com/learn/science/physics-university/physics-university-part-7/physics-university-part-7-concept-1)
- [Coulomb's law](https://studyvisually.com/learn/science/physics-university/physics-university-part-7/physics-university-part-7-concept-2)
- [Electric field](https://studyvisually.com/learn/science/physics-university/physics-university-part-7/physics-university-part-7-concept-3)
- [Field lines](https://studyvisually.com/learn/science/physics-university/physics-university-part-7/physics-university-part-7-concept-4)

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