AQA GCSE Physics

Revision Notes

6.2.3 EM Waves & Matter

Higher Tier Only

Interaction of Different Substances

  • When EM waves move from one medium to another the waves might be:
    • Transmitted
    • Absorbed
    • Reflected
    • Refracted

transmission-of-wave, IGCSE & GCSE Physics revision notes

When waves move from one medium to another they can be transmitted, reflected, refracted or absorbed

  • The material interacts differently with different parts of EM spectrum because of the difference in wavelength
  • Whilst some wavelengths might be transmitted, others might be reflected, refracted or absorbed
  • Which of the interactions happen depends on:
    • The wavelength of the waves
    • The material the wave is travelling through
  • For example, glass will:
    • Transmit and/or refract visible light
    • Absorb UV radiation
    • Reflect IR radiation
Higher Tier Only

Refraction of EM Waves

  • Some effects, for example, refraction, are due to the difference in velocity of the waves in different substances
  • Although all electromagnetic waves travel at the same speed in a vacuum, when they encounter certain materials (water, glass, oil) they will slow down
    • How much they slow down depends on the material
    • This slowing of electromagnetic waves causes them to refract
  • A simple example of this is the refraction of visible light when it enters (or leaves) a glass block, although other electromagnetic waves can also refract

refraction-through-different-blocks, IGCSE & GCSE Physics revision notes

When electromagnetic waves pass through matter, their interactions slow them down causing them to refract

Higher Tier Only

Wavefront Diagrams

  • When a wave hits a different medium the different parts of the wave enter the medium at different times
    • Hence, this leads to a change in speed
  • The difference in speed between the parts of the wave in the first medium and the parts in the second medium causes the wave to bend
    • Hence, this leads to a change in direction
  • Refraction can be represented using wavefront diagrams, as shown below:

wave-refraction, IGCSE & GCSE Physics revision notes

The different parts of the wave enter the second medium at different times causing the wave to bend

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