EM Waves & Matter (AQA GCSE Physics): Revision Note

Interaction of Different Substances

Higher Tier Only

• When EM waves move from one medium to another the waves might be:

  • Transmitted

  • Absorbed

  • Reflected

  • Refracted

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

Higher Tier 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

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

Wavefront Diagrams

Higher Tier 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:

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