Radio waves, light and gamma rays are the same kind of wave, differing only in wavelength and frequency. All are transverse and all travel at the same speed in a vacuum, the speed of light.
Electromagnetic waves are transverse and all travel at the same speed in free space, c = 3.0 × 10⁸ m s⁻¹. The spectrum runs from radio waves (longest wavelength, lowest frequency) through microwaves, infrared, visible light (400 nm to 700 nm), ultraviolet and X-rays to gamma rays (shortest wavelength, highest frequency). They obey c = fλ.
Move along the spectrum and watch the wavelength and frequency trade off through c = fλ, with the named regions and the narrow visible band highlighted.
Order matters: increasing frequency means decreasing wavelength.
| Region | Wavelength | Frequency |
|---|---|---|
| radio | longest wavelength | lowest frequency |
| microwave, infrared | ||
| visible | 400 nm to 700 nm | |
| ultraviolet, X-ray, gamma | shortest wavelength | highest frequency |
Four quick checks tied to this lesson. Each correct answer earns XP and lights this skill on your star map.
All electromagnetic waves travelling in a vacuum have:
Electromagnetic waves are:
Visible light has wavelengths in the approximate range:
Which of these has the longest wavelength?
Across the spectrum, only one quantity is shared in a vacuum.
Do not think shorter waves travel faster: in a vacuum all electromagnetic waves travel at the same speed c. Keep the visible range in the right units: 400 nm to 700 nm is 4 × 10⁻⁷ to 7 × 10⁻⁷ m. And electromagnetic waves are transverse, so unlike sound they can be polarised.
Unlocks once the checks above are done. Worth more XP, written to AS Paper 1 and 2 standard.
Light of frequency 5.0 × 10¹⁴ Hz travels in a vacuum at 3.0 × 10⁸ m s⁻¹. Its wavelength is:
Which list places the regions in order of increasing frequency?
X-rays and radio waves differ in their:
This skill is now lit gold on your star map. Keep the chain going.