© Oxford University Press 2011 IP Diffraction of waves Diffraction of waves

© Oxford University Press 2011 IP Diffraction of waves Whenever waves pass through a gap or move around an obstacle they spread out. This is called diffraction and it happens with either transverse or longitudinal waves.

© Oxford University Press 2011 IP Diffraction of waves Diffraction occurs all around us. Sound waves diffract when they go through an open doorway. This is why you can hear someone if they are talking outside the door.

© Oxford University Press 2011 IP Diffraction of waves The size of the gap and wavelength of the wave affect how much diffraction takes place. The best diffraction takes place when the gap is the same size as the wavelength.

© Oxford University Press 2011 IP Diffraction of waves Look at this picture again. Would the diffraction be greater or less if the sound was changed to a lower pitch?

© Oxford University Press 2011 IP Diffraction of waves Light has a very short wavelength so normally it is very difficult to observe diffraction. A CD acts as a diffract grating which causes light to diffract into a rainbow pattern.

© Oxford University Press 2011 IP Diffraction of waves Ultrasound also has a very short wavelength. Why does this make it good for medical imaging?