9. DIFFRACTION of waves and a scientific wave model

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• The scientific model of the diffraction of waves through a gap (or bending round a corner)

• Diffraction is the effect of waves spreading out when passing through a gap or passing by a barrier. In effect, waves go round corners! and it doesn't matter if its sound, light or water waves - they all diffract and bend round corners! The effect is so small with light (tiny wavelength), you don't notice it, but you see water waves bending around the walls of a harbour and you can hear sounds from round a corner.

• You should appreciate that significant diffraction only occurs when the wavelength of the wave is of the same order of magnitude as the size of the gap or obstacle.

• A: There is a relatively small diffraction effect when waves pass through a wide gap that is much bigger than the wavelength of the wave.

• B: You get the maximum spreading or diffraction when the waves pass through a gap of similar size to the wavelength of the incident waves.

• You can see these effects with transverse water waves at the seaside as waves hit the protective walls of a harbour BUT you need a very tiny slit to observe diffraction with light waves because of their tiny wavelength.

• Excluding satellite TV and radio, if it wasn't for diffraction you would never get a radio signal down in a valley - the radio waves bend over the hills!