# Electric current

The rate that charge flows past a point, I = Q/t. The unit is the ampere, one coulomb per second.

Physics (university) · Part 08: Circuits and magnetism · Card 1 of 12 · Last updated 2026-10-19

## Analogy

Water flow in a pipe: litres per second.

## Example

**Charge flow**

I = Q / t
I = 12 C / 4 s
I = 3 A

## In practice

12 C passing in 4 s is a current of 3 A.

## Questions people ask

### Which way does current flow?

By convention, current is the direction positive charge would move, from the positive terminal to the negative. In metal wires the real moving particles are electrons going the other way. The convention was set before electrons were discovered, and the maths works the same either way.

### What is the speed of electrons in a wire?

Electrons drift slowly, often less than a millimetre per second. The electric field travels along the wire near the speed of light, so a light turns on almost instantly. It is like a tube full of marbles: push one in and another pops out immediately.

## Related concepts

- [Ohm's law](https://studyvisually.com/learn/science/physics-university/physics-university-part-8/physics-university-part-8-concept-2)
- [Series and parallel resistors](https://studyvisually.com/learn/science/physics-university/physics-university-part-8/physics-university-part-8-concept-3)
- [Electric power](https://studyvisually.com/learn/science/physics-university/physics-university-part-8/physics-university-part-8-concept-4)
- [Kirchhoff's junction rule](https://studyvisually.com/learn/science/physics-university/physics-university-part-8/physics-university-part-8-concept-5)

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