Answer to Question #156521 in Physics for Jas

Question

This question concerns polarisation.

a) Explain what is meant by polarisation of a wave. This should include a mention of which types of wave can, and which cannot, be polarised (3 marks)

b) Explain why the two sheets of Polaroid will both allow light through in one orientation, but when one is rotated by 90o light is no longer transmitted.

Answer 1

a) What we call light waves are different waves that propagate in space in different directions and oriented differently. Polarization is the process of giving the wave a specific orientation, for example, vertical or horizontal. Since only transverse waves can be oriented such ways, polarization is only applicable for transverse waves. Longitudinal waves propagate along a straight line and cannot be polarized. For example, if we shine sunlight on a flat surface of a wooden table, the reflected light will be polarized. Light will be also polarized if we shine it on a flat glass surface. However, light will not be polarized after reflecting from a mirror because the metal atoms will get excited and produce additional waves. 

b) Also, we can use Polaroid glass to make the wave polarized. The Polaroid glass consists of special structures oriented in one direction like a fence. Thus, light that has been passed through one Polaroid glass is already polarized one way or another. When we attach the second Polaroid oriented the same way, the light still can pass it. However, if we turn one of the Polaroids 90 degrees (like one fence vertical and the other is horizontal), the transverse wave will not have a way to pass through them.