Wave behaviour at boundaries (Edexcel GCSE Physics): Revision Notes
Wave behaviour at boundaries
When a wave encounters a boundary between two different materials (a material interface), several things can happen depending on the properties of the materials and the wavelength of the wave.
1. Absorption:
Waves are absorbed by the second material. When this happens, the wave transfers its energy to the material. Often, this energy is transferred to the material's thermal energy store, leading to heating.
For example, when sunlight hits a black surface, the energy is absorbed and the surface heats up.
2. Reflection:
Waves are reflected off the boundary between the two materials. The wave is neither absorbed nor transmitted, but instead bounces back from the second material. This is how echoes are created when sound waves reflect off hard surfaces like walls or cliffs.
In reflexion:
- The angle of incidence (incoming angle) is equal to the angle of reflexion (outgoing angle).
3. Transmission and Refraction:
Waves are transmitted through the second material. When waves pass into the second material, they may change direction. This change in direction is called refraction.
Refraction occurs because the wave changes speed as it enters a new material, which can make it bend.
For example:
- Light waves bend when they pass from air into glass or water.
Refraction is used in:
- Lenses (e.g., glasses, camera lenses) to focus light.
- Communication systems, like fibre optics, to transmit data.
What Determines Wave Behaviour?
The way a wave behaves at a boundary depends on:
- The wavelength of the wave (e.g., shorter wavelengths are more likely to be reflected).
- The properties of the material (e.g., denser materials may absorb or refract more energy).