Explain why radio waves spread out more than visible light when each passes through a gap of the same width.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Radio waves and visible light are both electromagnetic waves. When each passes through a gap of the same width, radio waves spread out much more than visible light.
Model answer (5 marks)
Both radio waves and visible light undergo diffraction when passing through a gap.
The amount of diffraction depends on the ratio of the wavelength (λ) to the width of the gap (a).
Radio waves have a much longer wavelength than visible light.
For the same gap width, the radio wave’s wavelength is closer to, or even comparable with, the gap width, whereas visible light’s wavelength is much smaller than the gap.
Consequently, the radio waves diffract – i.e. spread out – significantly more than visible light when they pass through the same gap.
The amount of diffraction depends on the ratio of the wavelength (λ) to the width of the gap (a).
Radio waves have a much longer wavelength than visible light.
For the same gap width, the radio wave’s wavelength is closer to, or even comparable with, the gap width, whereas visible light’s wavelength is much smaller than the gap.
Consequently, the radio waves diffract – i.e. spread out – significantly more than visible light when they pass through the same gap.
Examiner tips
- Use the word ‘diffraction’ and link it to the λ/a ratio; mention that a larger λ/a gives more spreading.
- Show the logical chain: both diffract → amount depends on λ/a → radio λ >> visible λ → λ/a larger for radio → more spreading.
Common mistakes
- Confusing refraction with diffraction; stating only that radio waves are longer without linking to diffraction.
- Giving a qualitative answer without mentioning the λ/a relationship or the comparison of wavelengths.
Mark scheme (5 marks)
- Both radio waves and visible light undergo diffraction when passing through a gap
- The amount of diffraction depends on the relationship between wavelength and gap width
- Radio waves have a much longer wavelength than visible light
- For the same gap width, the radio wave's wavelength is closer to / more comparable to the gap width than visible light's wavelength
- Therefore radio waves diffract (spread out) significantly more than visible light through the same gap
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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