Radio waves are used for broadcasting television and radio signals. Explain why radio waves are reflected by the ionosphere and why this property is useful for broadcasting signals across long distances on Earth.

Pearson Edexcel International GCSE Physics (4PH1) — 3.2 The electromagnetic spectrum · Explain · 4 marks · View as Markdown

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

Radio waves are part of the electromagnetic spectrum and have the longest wavelengths and lowest frequencies of all electromagnetic waves. They travel at 3 × 10⁸ m/s in a vacuum.

Model answer (4 marks)

Radio waves have long wavelengths (low frequencies) and are reflected by the ionosphere, a layer of the atmosphere. The ionosphere sends the waves back down towards the Earth’s surface, allowing them to travel beyond the horizon and reach receivers far away on the curved surface of the Earth.

Examiner tips

  • Use the word "reflected" and mention the ionosphere as a layer of the atmosphere.
  • Explain that long wavelengths allow reflection and that this sends the waves back to Earth.
  • Show how this lets signals reach beyond the horizon.
  • Keep the answer concise and use the exact terminology.

Common mistakes

  • Confusing refraction with reflection.
  • Failing to mention the ionosphere as a layer of the atmosphere.
  • Not linking the reflection to the ability to reach receivers beyond the horizon.

Mark scheme (4 marks)

  1. Radio waves have a long wavelength (and low frequency)
  2. Radio waves are reflected by the ionosphere (a layer of the atmosphere)
  3. Reflection by the ionosphere sends the radio waves back down towards Earth's surface
  4. This allows radio waves to travel beyond the horizon / reach receivers far away on Earth's curved surface

Key terms in this question

radio waves · ionosphere

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