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PhysicsInternational GCSEEdexcel & Cambridge (CIE)Years 10–11

IGCSE Physics The 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.

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Key concepts

The order
Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma — increasing frequency and energy, decreasing wavelength.
Common properties
All EM waves are transverse, transfer energy and travel at 3 × 10⁸ m/s in a vacuum.
Uses and dangers
Higher-frequency waves (UV, X-ray, gamma) carry more energy and can ionise cells, causing damage.
  • Radio waves are used for broadcasting; microwaves for cooking and satellite communication.
  • Infrared is used for heating and remote controls; visible light for sight and fibre optics.
  • X-rays and gamma rays are ionising and used in medical imaging and treatment.

Key formulas

Wave equation

v = f × λ

for EM waves v ≈ 3 × 10⁸ m/s in a vacuum.

Worked example

List the EM spectrum in order of increasing frequency.

  1. 1Start with the lowest frequency: radio.
  2. 2Then microwave and infrared.
  3. 3Then visible light and ultraviolet.
  4. 4End with the highest: X-rays and gamma rays.

Answer: Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma

Common mistakes

✗ Getting the order the wrong way round.

✓ Use a mnemonic; radio has the longest wavelength and lowest frequency.

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

✓ They all travel at 3 × 10⁸ m/s in a vacuum.

✗ Confusing uses of neighbouring waves.

✓ Learn one clear use and danger for each band.

Quick check

Try these, then reveal the answers.

Which EM wave has the longest wavelength?Reveal answer

Radio waves.

Which EM waves are ionising?Reveal answer

Ultraviolet, X-rays and gamma rays.

What speed do all EM waves travel at in a vacuum?Reveal answer

3 × 10⁸ m/s.

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Exam tips

  • Memorise the order with a mnemonic to avoid mixing up bands.
  • Match each wave to one use and one danger for full marks.
  • Link higher frequency to higher energy and greater ionising risk.

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Key terms explained

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Frequently asked questions

Why are gamma rays dangerous?+

They are highly ionising, carrying enough energy to damage or kill living cells and cause mutations.

Do all EM waves travel at the same speed?+

Yes, in a vacuum they all travel at 3 × 10⁸ m/s; they differ in frequency and wavelength.

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