Wave Interactions
- 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