Unit 12, lesson 56. About 15 minutes.

The electromagnetic spectrum

What do radios, microwaves, rainbows and X-rays all have in common?

Play

Getting the experiment ready…

Explain

Light is only a tiny part of a huge family of waves, called electromagnetic waves.

From longest to shortest, they are radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.

All of them travel at the speed of light. Slide along to compare them.

All electromagnetic waves travel through space at c, so c = f × λ.

Shorter wavelengths have higher frequencies and carry more energy per photon. Ultraviolet, X-rays and gamma rays can damage cells.

Worked example: green light has λ = 5 × 10⁻⁷ m. So f = 3 × 10⁸ / 5 × 10⁻⁷ = 6 × 10¹⁴ Hz.

Long radio waves
Light we can see
Short gamma rays

Want the full story?

The bands overlap, and the boundaries in the sim are approximate. All these waves are made of electric and magnetic fields that vibrate together, as James Clerk Maxwell predicted. A microwave oven heats food by making its water molecules jostle.

The Formula

speed of light = frequency × wavelength

c = f \times \lambda

$c$: the speed of light, about 3 × 10⁸, measured in metres per second (m/s)
$f$: the frequency, measured in hertz (Hz)
$\lambda$: the wavelength, measured in metres (m)

Try the numbers

Wavelength, as a power of 10 metres: -6.3

Frequency: 5.98 × 10¹⁴ Hz

Try it at home

You need a TV remote, a phone camera.

You need: a TV remote, a phone camera.

Point a TV remote at a phone camera.
Press a button, and look at the screen.
See the flashing light that your eyes can't see.

What's happening: many cameras can pick up the infrared flashes that remotes use.

Physics is life

Your body

Your skin feels infrared.

You feel infrared as warmth, and ultraviolet can burn your skin.

Daily life

Phones use radio waves.

Phones, Wi-Fi and radios all use invisible electromagnetic waves.

Nature

Bees see ultraviolet.

Bees see ultraviolet patterns on flowers, which are invisible to us.

Space

Telescopes see all kinds of light.

Telescopes detect every band, showing the universe in ways that eyes can't.

Quick check

Question 1 of 3

Which has the longest waves?

Words to know

Electromagnetic waves: Waves of electric and magnetic energy, including light and radio.

Electromagnetic waves: Waves of electric and magnetic energy, including light and radio.
Wavelength: The distance from one wave crest to the next.
Frequency: How many waves pass each second. It is measured in hertz.

Meet the scientist

Next up

Inside the atom