| In order to fully understand the geometry of
diffraction, it is important to understand how radiation waves (x-rays and
electrons) add together when there is a phase difference between them. Here we
look at adding together two waves of the same amplitude and frequency, with a
phase difference between them. This is also
called superposition.
 Use the slider to change
the phase difference between the blue and red sine waves. The resultant
addition of these two waves is shown as the yellow curve.
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Answer the following
questions:
For the condition of constructive interference (maximum resultant) we say that
the individual waves are in phase. The phase difference which gives this condition is 0,
360, 720 etc. degrees, or in terms of wavelength this is 0, l,
2l etc.
For the condition of destructive interference (minimum resultant) we say that
the individual waves are out of phase. The phase difference which gives this condition is
180, 540, etc. degrees, or in terms of wavelength this is l/2,
3l/2 etc.
