Revisiting waves

Frequency, amplitude, delayed copying

You describe a wave by setting the amplitude, the frequency, and the delay between source and detector (set by the distance and wave speed).

To-and-fro and up-and-down

The vibrating can be to-and-fro(longitudinal waves), or up-and-down(transverse waves).

Electromagnetic waves, used to describe light, radio and radar as well as other radiations, are transverse waves.


The magnetic vibration is at right angles to the electric vibration, and both are at right angles to the direction the wave travels.

Polarisation and matter

If the up-and-down vibrations are all in the same plane, then the wave is polarised.

Light that bounces off water or snow is polarised: that's why Polaroid sunglasses work so well for skiers, sailors and anglers. Light from lamps and torches is usually unpolarised.