Infrared radiation, microwaves and radio waves are all found in the electromagnetic spectrum. A student claims that these three types of radiation are fundamentally the same kind of wave. Justify the student's claim, and state the correct order of these three types of radiation from lowest frequency to highest frequency.

Eduqas GCSE Physics — 6.1 Frequency range of the spectrum · Justify · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

All electromagnetic waves are transverse waves, so infrared, microwaves and radio waves share the same wave nature.
All electromagnetic waves travel at the same speed in a vacuum – the speed of light (3×10⁸ m/s). Therefore they are fundamentally the same type of wave.
The correct order from lowest to highest frequency is: radio waves → microwaves → infrared.

Examiner tips

  • Use the word ‘transverse’ to show you know the wave type. Mention the common speed (3×10⁸ m/s) to link the three. State the order clearly and in the correct direction (lowest to highest).

Common mistakes

  • Confusing wavelength with frequency. Listing the order incorrectly (e.g., infrared first). Omitting the fact that all EM waves travel at the speed of light.

Mark scheme (4 marks)

  1. All electromagnetic waves are transverse waves
  2. All electromagnetic waves travel at the same speed in a vacuum / the speed of light (3 × 10⁸ m/s)
  3. Radio waves have the lowest frequency of the three
  4. Correct full order: radio waves → microwaves → infrared (lowest to highest frequency)

Key terms in this question

electromagnetic spectrum · frequency

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