EM Waves & Matter (Edexcel GCSE Physics: Combined Science)

• When EM waves interact with matter, they might move from one medium to another
• Sometimes EM waves will undergo refraction
  • This happens 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 (such as water, glass or 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. The red lines are the rays and black lines are the normals

Higher Tier Only

• When EM interact with matter, they slow down
  • The denser the substance, the slower the wave

• Different wavelengths can slow down by different amounts – an effect known as dispersion
• This effect is seen clearly with visible light and is responsible for the separation of white light into its constituent colours when it passes through a prism
  • This is done by refraction
  • Violet light is refracted the most, whilst red light is refracted the least
  • This splits up the colours to form a spectrum

• This process is similar to how a rainbow is created

White light may be separated into all its colours by passing it through a prism

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