EM Waves & Matter (AQA GCSE Physics)

Revision Note

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Katie M

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Katie M

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Interaction of Different Substances (HT only)

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

transmission-of-wave-igcse-and-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

Refraction of EM Waves (HT only)

  • 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

Katie M, Physics

Teacher tip

Katie M

Physics

In my experience of teaching refraction to GCSE students, the most difficult part is remembering which way the light bends. I give my students a thought experiment so they can always work it out.

Imagine that I let you out for break now, the corridor would be empty and you can head straight for any door you choose. Now imagine that I let you out for break two minutes after the bell goes. The corridor would be full, and you get pushed along the corridor stuck in the middle of the crowd of students. That's a bit like what happens to a light ray. When the light ray passes into a denser medium, that's like the busy corridor, it bends toward the normal. When the light ray enters a less dense material, that's the empty corridor, it bends away from the normal. 

Wavefront Diagrams (HT only)

  • 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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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.