IGCSE 0625 / Section 3.3 / Core

One family, many wavelengths.

Radio waves, the light you see, and the gamma rays from space are all the same kind of wave, differing only in wavelength. Lined up shortest to longest they make one continuous spectrum, all racing through space at the same speed.

The key idea

All electromagnetic waves are transverse and travel at 3 x 10⁸ m/s in a vacuum. From radio waves to gamma rays the wavelength gets shorter and the frequency higher. Visible light is only a thin band in the middle.

Definition · learn the exact words

The electromagnetic spectrum is the family of transverse waves that all travel at the same speed in a vacuum, 3 x 10⁸ m/s, arranged in order of wavelength from radio waves (longest) to gamma rays (shortest).

c = f λ  (c = 3 x 10⁸ m/s in a vacuum)

Order: radio, microwave, infrared, visible, ultraviolet, X-rays, gamma. Along it the wavelength falls and the frequency rises.

Section 01

Sweep across the spectrum.

Move along the bands from radio to gamma and watch the wavelength shorten and the frequency climb.

Stage 1 · Learn

Check regions

Four quick checks. Each correct answer earns XP and lights this skill on your star map.

Quick check+10 XP

Which region of the electromagnetic spectrum has the longest wavelength?

Quick check+10 XP

In a vacuum, all electromagnetic waves travel at...

Quick check+10 XP

Visible light sits in the spectrum between...

Quick check+10 XP

A common use of infrared radiation is in...

Section 02

Seven bands, one speed.

The regions differ in wavelength and frequency, but in a vacuum they all travel at the same speed.

Worked example

A microwave has a wavelength of 0.020 m. Find its frequency in a vacuum.

Step 1 · Write the relationc = f λ, so f = c ÷ λ
Step 2 · Substitutef = (3 x 10⁸) ÷ 0.020
Step 3 · Answerf = 1.5 x 10¹⁰ Hz
Examiner trap

Every electromagnetic wave travels at the same speed in a vacuum, whatever its frequency. What changes across the spectrum is the wavelength and frequency, not the speed. Visible light is only a thin slice sitting between infrared and ultraviolet.

Stage 2 · Exam

Exam-style questions

Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.

Finish the four checks above to unlock the exam questions
Exam style+20 XP

A type of radiation is used both to cook food and to carry mobile phone and satellite signals. It is...

Exam style+20 XP

Which region of the spectrum has the highest frequency?

Exam style+20 XP

A radio wave has a wavelength of 1500 m. Its frequency in a vacuum is about...

Skill unlocked

Regions, mastered.

The electromagnetic spectrum is mapped. Keep the chain going.

-Rank -Level -Score -Topics
Go deeper · practice
Six original Cambridge-style questions
The order of the spectrum from radio to gamma, the shared speed in a vacuum, the c = f times wavelength relation, and the main uses. Attempt each, then reveal the worked solution.
Stage 3 · master the unit
Waves challenge
Mixed questions across the whole unit, each one worth XP. Start this only when you feel confident across every topic in the unit, not just regions.
Start the unit challenge →