Wavefronts & Rays
- Waves can travel in both two and three-dimensions:
- A surface wave propagates in two dimensions and has circular wavefronts (like a circle) such as the surface of water
- A spherical wave propagates in three dimensions and has spherical wavefronts (like a sphere) such as sound or light
A surface wave has circular wavefronts and moves in two-dimensions propagating outwards from the point source
A three dimensional wave moves with spherical wavefronts in three dimensions like a sphere
- Waves can be represented graphically in two different ways:
- Wavefronts - lines joining all the points that oscillate in phase and are perpendicular to the direction of motion (and energy transfer)
- Rays - lines showing the direction of motion (and energy transfer) of the wave perpendicular to the wavefront
Wavefronts and rays for transverse waves travelling in a horizontal plane
- Wavefronts are viewed from above and look like a series of parallel vertical lines
- Peaks are often represented with a darker line
- Troughs are represented with a fainter line
- Some diagrams use only peak wavefronts
Waves can be represented using wavefronts, sometimes diagrams show peak wavefronts and trough wavefronts
- The distance between successive peak wavefronts or (trough wavefronts) is equal to the wavelength of the waves
Examiner Tip
Understanding the difference between circular and spherical wavefronts is tricky. Remember that a circle is a 2D shape, so circular wavefronts are 2D and a sphere is a 3D shape, so spherical wavefronts are 3D.
Exam questions may ask you to sketch or interpret wavefronts and rays. Make sure you draw these with a ruler to ensure your lines are straight. Unclear or slopping diagrams are unlikely to get full marks!
