# Inductance

A coil's resistance to changing current. The voltage across it is L x change in I / change in t. It stores energy 1/2 L I squared.

Physics (university) · Part 09: Induction, light and optics · Card 4 of 11 · Last updated 2026-10-19

## Analogy

A heavy flywheel for current.

## Example

**Inductor**

V = L x change in I / time
= 2 x 3 / 0.5
= 12 V

## In practice

A 2 H inductor with current changing by 3 A in 0.5 s has 12 V across it.

## Questions people ask

### Why does an inductor resist sudden changes in current?

A changing current changes its own magnetic flux, which induces a voltage that opposes the change, as Lenz's law says. So current cannot jump instantly. This is why switching off a coil can make a spark, because the field collapses quickly and produces a large voltage.

### Where is energy stored in an inductor?

In the magnetic field inside the coil, with energy 1/2 L I squared. When the current falls, the field shrinks and returns the energy to the circuit. This is similar to a capacitor storing energy in its electric field, but with current in place of voltage.

## Related concepts

- [Magnetic flux](https://studyvisually.com/learn/science/physics-university/physics-university-part-9/physics-university-part-9-concept-1)
- [Faraday's law](https://studyvisually.com/learn/science/physics-university/physics-university-part-9/physics-university-part-9-concept-2)
- [Lenz's law](https://studyvisually.com/learn/science/physics-university/physics-university-part-9/physics-university-part-9-concept-3)
- [Transformer](https://studyvisually.com/learn/science/physics-university/physics-university-part-9/physics-university-part-9-concept-5)

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