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PhysicsGCSEAQA & EdexcelYears 10–11

GCSE Physics Electromagnetic Spectrum Notes

The electromagnetic spectrum is a family of transverse waves that all travel at the speed of light in a vacuum. Learn the order, uses and dangers for reliable marks.

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Key concepts

The seven waves
In order of increasing frequency (decreasing wavelength): radio, microwave, infrared, visible light, ultraviolet, X-rays and gamma rays.
Shared properties
All EM waves are transverse and travel at 3 × 10⁸ m/s in a vacuum. Higher frequency means higher energy.
Uses and dangers
Higher-frequency waves (UV, X-rays, gamma) carry more energy and are more dangerous because they can ionise atoms and damage cells.
  • Radio waves: broadcasting and communications. Microwaves: cooking and satellite/phone signals.
  • Infrared: heating, remote controls and thermal imaging. Visible light: seeing and fibre-optic cables.
  • UV: security marking and sunbeds (can cause skin cancer). X-rays: medical imaging. Gamma: sterilising and treating cancer.

Worked example

List the electromagnetic spectrum in order of increasing frequency and state whether wavelength increases or decreases.

  1. 1Start from the lowest frequency: radio, microwave, infrared.
  2. 2Continue: visible light, then ultraviolet.
  3. 3Finish with the highest frequency: X-rays, then gamma rays.
  4. 4State the trend: as frequency increases, wavelength decreases.

Answer: Radio → microwave → infrared → visible → ultraviolet → X-ray → gamma; wavelength decreases as frequency increases.

Common mistakes

✗ Getting the order of the spectrum wrong.

✓ Use a mnemonic, e.g. 'Raging Martians Invaded Venus Using X-ray Guns'.

✗ Thinking EM waves travel at different speeds in a vacuum.

✓ All EM waves travel at the same speed (3 × 10⁸ m/s) in a vacuum.

✗ Saying all EM waves are dangerous.

✓ Only high-frequency waves (UV, X-rays, gamma) are ionising and harmful in high doses.

Quick check

Try these, then reveal the answers.

Which EM wave has the longest wavelength?Reveal answer

Radio waves.

Which three EM waves are ionising and can damage cells?Reveal answer

Ultraviolet, X-rays and gamma rays.

What is a use of infrared radiation?Reveal answer

Heating, remote controls or thermal imaging.

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Exam tips

  • Learn the order in both directions — questions can ask for increasing or decreasing frequency.
  • Link danger to frequency and energy: higher frequency → more energy → more harmful.
  • For 'uses' questions, match each wave to a specific application.

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Frequently asked questions

Why are gamma rays more dangerous than radio waves?+

Gamma rays have a much higher frequency and energy, so they can ionise atoms and damage or kill living cells, whereas low-energy radio waves cannot.

Do all electromagnetic waves travel at the same speed?+

Yes — in a vacuum all EM waves travel at the speed of light, 3 × 10⁸ m/s; they differ in frequency and wavelength.

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