Polarisation is a wave property which allows us to distinguish between transverse and longitudinal waves.
Light is a transverse wave and this can be shown by polarising it. Light consists of vibrations of electric and magnetic fields travelling through space. Light which is unpolarised (such as the light emitted by the Sun, or by a light bulb) has vibrations in all directions at right angles to the direction in which it is travelling.
When the light passes through a piece of Polaroid (a polarising filter), it becomes polarised. Polaroid consists of long-chain molecules that absorb the energy from the oscillating electric field. If these molecules are arranged vertically, they absorb light waves which are polarised vertically, that is, light waves whose electric field is oscillating up and down. Horizontally polarised light waves (whose electric field is oscillating from side to side) pass through unaffected. The light is now described…