Explain why radio waves are used to transmit signals over long distances through the atmosphere, whilst gamma rays are not used for this purpose.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Broadcasting companies transmit television and radio signals across the country using different parts of the electromagnetic spectrum. The choice of wave depends on the properties of that part of the spectrum.
Model answer (4 marks)
All electromagnetic waves travel at the same speed in a vacuum and, to a good approximation, through the atmosphere.
Radio waves have a long wavelength and low frequency compared with gamma rays.
Because of their long wavelength, radio waves are not significantly absorbed by the atmosphere and can therefore propagate over long distances.
Gamma rays have a very short wavelength and high frequency; they are strongly absorbed by the atmosphere, are ionising and harmful, and therefore do not penetrate the atmosphere over long distances.
Radio waves have a long wavelength and low frequency compared with gamma rays.
Because of their long wavelength, radio waves are not significantly absorbed by the atmosphere and can therefore propagate over long distances.
Gamma rays have a very short wavelength and high frequency; they are strongly absorbed by the atmosphere, are ionising and harmful, and therefore do not penetrate the atmosphere over long distances.
Examiner tips
- State the common speed of EM waves first to show understanding of the spectrum.
- Mention wavelength/frequency difference to justify radio wave choice.
- Explain atmospheric absorption for radio vs gamma rays.
- Keep answer concise and use exam terminology.
Common mistakes
- Confusing speed of EM waves with speed of light in different media.
- Forgetting to mention absorption or ionising nature of gamma rays.
- Using vague terms like "short" or "long" without linking to wavelength or frequency.
Mark scheme (4 marks)
- All electromagnetic waves travel at the same speed in a vacuum / through the atmosphere
- Radio waves have a long wavelength / low frequency compared to gamma rays
- Radio waves are not absorbed (significantly) by the atmosphere / can pass through the atmosphere
- Gamma rays are absorbed by the atmosphere / gamma rays are ionising and harmful / gamma rays do not penetrate the atmosphere over long distances
Key terms in this question
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →