# Electromagnetic wave

A wave of oscillating electric and magnetic fields that travels through empty space at c = 3.00e8 m/s.

Physics (university) · Part 09: Induction, light and optics · Card 6 of 11 · Last updated 2026-10-19

## Analogy

Two fields pushing each other along, needing no medium.

## Example

**Radio wave**

lambda = c / f
= 3e8 / 1e8
= 3 m

## In practice

A 100 MHz radio wave has a wavelength of 3 m.

## Practice

### Flashcards

- **How fast do EM waves travel in a vacuum?** About 3.00e8 m/s.

## Questions people ask

### How did Maxwell predict light?

Maxwell's equations showed that a changing electric field makes a magnetic field and vice versa. His equations gave a wave speed equal to 1 over the square root of mu0 epsilon0, which matched the measured speed of light. He concluded that light is an electromagnetic wave.

### Do EM waves need a medium?

No. They are self-sustaining oscillations of electric and magnetic fields, so they travel through a vacuum. Sunlight crosses about 150 million kilometres of empty space to reach Earth. In materials such as glass or water, the waves slow down but keep going.

## Related concepts

- [Electromagnetic spectrum](https://studyvisually.com/learn/science/physics-university/physics-university-part-9/physics-university-part-9-concept-7)
- [Snell's law](https://studyvisually.com/learn/science/physics-university/physics-university-part-9/physics-university-part-9-concept-8)
- [Total internal reflection](https://studyvisually.com/learn/science/physics-university/physics-university-part-9/physics-university-part-9-concept-9)
- [Thin lens equation](https://studyvisually.com/learn/science/physics-university/physics-university-part-9/physics-university-part-9-concept-10)

Web page: https://studyvisually.com/learn/science/physics-university/physics-university-part-9/physics-university-part-9-concept-6
Study this card in the app: https://studyvisually.com/app/learn?category=physics-university&card=physics-university-part-9-concept-6