Reflection, Refraction and Wave Behaviour — AQA GCSE Physics
Waves can be reflected, transmitted, refracted or absorbed when they meet a boundary between materials.
Wave types recap
- Transverse waves — oscillations are perpendicular to the direction of energy transfer (e.g. EM waves, water waves).
- Longitudinal waves — oscillations are parallel to the direction of energy transfer (e.g. sound), with compressions and rarefactions.
At a boundary
When a wave meets a boundary between two materials it can be:
- reflected (bounces back),
- transmitted (passes through — often refracted), or
- absorbed (energy transferred to the material).
Reflection
In reflection, the angle of incidence equals the angle of reflection, both measured from the normal (the line at 90° to the surface).
- Specular reflection — from a smooth surface (a clear image, e.g. a mirror).
- Diffuse reflection — from a rough surface (light scattered in all directions).
Refraction
Refraction is the change in direction of a wave when it crosses a boundary and changes speed:
- entering a denser material, a wave slows down and bends towards the normal;
- entering a less dense material, it speeds up and bends away from the normal.
The frequency stays the same; the speed and wavelength change.
Exam tips
- At a boundary a wave can be reflected, refracted (transmitted) or absorbed.
- Reflection: angle of incidence = angle of reflection (from the normal).
- Refraction is caused by a change in wave speed at a boundary.
- Distinguish specular (smooth) and diffuse (rough) reflection.