Wave Interactions (Edexcel GCSE Physics)

• When a wave reaches an interface (or boundary) between two materials - for example, air and water - the wave may be:
  • Reflected
  • Refracted
  • Transmitted
  • Absorbed

Reflection

• Reflection occurs when:

A wave hits a boundary between two media and does not pass through, but instead stays in the original medium

• Some of the wave may also be absorbed or transmitted
  • Echos are examples of sound waves being reflected off a surface

• Flat surfaces are the most reflective
  • The smoother the surface, the stronger the reflected wave is

• Rough surfaces are the least reflective
  • This is because the light scatters in all directions

• Opaque surfaces will reflect light which is not absorbed by the material
  • The electrons will absorb the light energy, then reemit it as a reflected wave

Refraction

• Refraction occurs when:

A wave changes speed at the boundary between two materials of different densities

• Glass and water are both denser than air, so light waves passing from air into them will slow down (and speed up if going from them into air)
• The change in speed at the boundary can sometimes causes the wave to change direction
  • Lenses make use of refraction to bend light waves and help focus it in glasses and cameras

• Sound, water, electromagnetic and seismic waves can all be refracted

Transmission

• Transmission occurs when:

A wave passes through a substance

• For light waves, the more transparent the material, the more light will pass through
• Transmission can involve refraction but is not exactly the same
• For the process to count as transmission, the wave must pass through the material and emerge from the other side

• When passing through a material, waves are usually partially absorbed
• The transmitted wave may have a lower amplitude because of some absorption
  • For example, sound waves are quieter after they pass through a wall

When a wave passes through a boundary it may be absorbed and transmitted

Absorption

• Absorption occurs when:

Energy is transferred from the wave into the particles of a substance

• Waves can be partially or completely absorbed
  • Sound waves are absorbed by brick or concrete in houses

• Light will be absorbed if the frequency of light matches the energy levels of the electrons
  • The light will be absorbed, and then reemitted over time as heat

• If an object appears red, this means:
  • Only red light has been reflected
  • All the other frequencies of visible light have been absorbed

The object is seen as red since the red light is reflected whilst the other colours are absorbed