Light
Science Practicals: GCSE, topic 3.1.10
Waves at a Boundary
When waves travel from one medium to another, their speed and wavelength change but their frequency stays the same.
Speed and wavelength change
- The speed of a wave changes when it travels from one medium to another.
- The wavelength of a wave also changes when it travels from one medium to another.
- The speed and the wavelength are directly proportional:
- If the speed doubles, the wavelength doubles.
- If the speed halves, the wavelength halves.
Frequency is unchanged
- The frequency of the wave does not change because the source is producing the same number of oscillations (vibrations) per second.
Waves at a Boundary
Waves can be reflected, refracted, absorbed and transmitted (passes through) at the boundary between one medium (material) and another. The way in which these processes happen varies with wavelength.
Refraction
- A wave’s speed can change when moving from one medium to another.
- If the wave crosses to the new medium at an angle (not 90 degrees), the change in the wave’s speed will cause the direction of the wave’s motion to change and the wave will appear to bend.
- This is called refraction.
-min,w_800.jpg)
Reflection
- Reflection happens when a wave hits a flat surface (plane) and bounces off.
Absorption
- When waves meet some materials, the energy is absorbed by the material.
- For example, when light falls on a matt black surface, most of the energy is absorbed.
Transmission
- Waves carry on travelling through a new material.
- This often leads to refraction.
Test yourself on Light
Which of these are true of waves at a boundary?
Which of these does not change when a wave crosses a boundary between two substances?
Which of these can happen to a wave at a boundary?