Reflection, Refraction & Transmission
- When waves arrive at a boundary between two materials, they can be:
- Reflected
- Refracted
- Transmitted
Reflection
- Reflection occurs when:
A wave hits a boundary between two media and does not pass through, but instead bounces back to the original medium
- The law of reflection states:
The angle of incidence, i = The angle of reflection, r
Reflection of a wave at a boundary
- When a wave is reflected, some of it may also be absorbed by the medium, transmitted through the medium, or polarised
- At a boundary between two media, the incident ray is the ray that travels towards the boundary
- During reflection, the frequency, wavelength and speed of the wave does not change
Refraction
- When light crosses the boundary between two media with different optical densities, it refracts
- Refraction occurs when:
A wave changes speed and direction at the boundary between two media
Refraction of a ray between water and air
- This is due to the density of the media
- If the medium is more dense, the wave slows down
- If the medium is less dense, the wave speeds up
- In this case, water is denser than air
- When a wave refracts, its speed and wavelength change, but its frequency remains the same
- This is noticeable by the fact that the colour of the wave does not change
- An example of water waves refracting is when they travel from deeper to shallower water
- The wavelength of the waves decreases in the shallower water
Water waves being refracted at the boundary between deep and shallow water
Transmission
- Transmission occurs when:
A wave passes through a substance
- Refraction is a type of transmission
- Transmission is the more general term for a wave appearing on the opposite side of a boundary (the opposite of reflection)
- Refraction is specifically the change in direction of a wave when it crosses a boundary between two materials that have a different density
- When passing through a material, waves can be partially absorbed
- The transmitted wave will have a lower amplitude if some absorption has occurred
When a wave passes through a boundary it may be absorbed and transmitted
- During transmission, the frequency or speed of the wave does not change
- Reflection, refraction and transmission occur for all types of waves, both transverse and longitudinal
Exam Tip
You must be able to differentiate between the different types of wave behaviour. Refraction and reflection is commonly mixed up. With refraction, there is always transmission and a change in direction in another medium. With reflection however, there is no transmission into another medium.