IGCSE Online Tutorial - Jesmul Sir's Portal

IGCSE Online Tutorial - Jesmul Sir's Portal

Physics GCSE: Properties of Waves

Diffraction of waves

Diffraction of water waves

Have you ever tried squashing plasticine through a small hole? Perhaps not, but if you have you may have noticed that it makes a bulge as it comes through the hole. The same thing happens to waves as they travel through small holes, or push past obstacles.
As the water waves go through the gap they spread out, this is called diffraction.

The longer the wavelength of the wave the larger the amount of diffraction.

The greatest diffraction happens when the gap size is about the same size as the wavelength.

Diffraction of light and sound waves

Diffraction of sound and light happens in the same way as water waves. There are just a few extra points to remember:

Diffraction of light

Light waves have a very short wavelength compared to water waves. Diffraction is most noticeable when the gap size is about the same as the wavelength of the wave. Therefore to diffract light the gap needs to be extremely small, in fact around one thousandth of a millimetre.

Diffraction of sound

Sound has a much longer wavelength than light. Sound waves can even diffract around buildings or through doorways. This is why you can often hear people when you can't see them.

As with all wave diffraction the amount of diffraction will depend on the wavelength of the sound wave and the size of the gap the wave is travelling through.

Sound waves are diffracted as they leave their source, for instance a loud speaker. The size of the source will affect how much diffraction occurs. 
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