Observation The four phenomena should be clearly seen as illustrated in Fig 10.15(a) to (d).
Deep
Shallow (a) (b) Fig 10.15 Polarisation
POLARISATION Polarisation is when the direction of vibration of a wave is restricted to one plane.
Only transverse waves can be polarised.The fact that light can be polarised proves it is a transverse wave.3
Doppler Effect LAWS AND PRINCIPLES
Doppler Effect The Doppler Effect is the apparent change in frequency of waves due to the relative motion between a wave source and observer.
Source not moving Direction of motion of source
Vertically polarised wave
Fig 10.16: Illustration of polarisa- tion of a transverse wave
Light Passing through Crossed Polarisers
Polariser 1 (vertical)
Incident beam (unpolarised)
Polariser 2 (horizontal)
(c) (d)
3 AX B Y Z
Source was at the same position when all three crests were emitted
(a)
Source was at X when Crest 1 was emitted.
Source was at Y when Crest 2 was emitted.
(b)
Fig 10.17: Illustration of the Doppler Effect: (a) waves from a source that is not moving; (b) waves from a source moving to the right at speed u m s1
3Polarisation will be dealt with in more detail in Chapter 14. WAVES 163
