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• Principle of Superposition
• Interference
• Path difference

Here we go:

What is superposition?
Multiple waves passing through the same point.

What is interference?
The phenomena that occurs when waves superpose – it is described through the principle of superposition.

What is the principle of superposition?
“When multiple waves pass through a point, the resultant displacement at that point is equal to the sum of the displacements of individual waves at that point.”

Example: 2 Individual Waves Interfering

There are 2 Types of Interference:

Constructive Interference	Crest + Crest OR Trough + Trough Displacements ADD UP to have a larger value Maximum displacement
Destructive Interference	Crest + Trough Displacements CANCEL OUT to have smaller value For identical waves, 0 displacement

However, interference can happen between ANY waves as long as they are in the same medium.

Waves with different frequencies, amplitudes, or phase can interfere – the principle of superposition will be true: the resultant displacement = sum of individual displacements.

A Classic Example: 2 Wave Sources

When two point sources emit waves radially, the waves can interfere & form alternating patterns. This is due to path difference.

What is a path difference?
The difference in length travelled by 2 waves across a path from a SOURCE to a POINT where they superpose.

When path difference is a WHOLE multiple of λ:	Maximum constructive interference
When path difference is an ODD multiple of λ/2:	Maximum destructive interference (antiphase)
Otherwise:	A combination

Now that you know the basics of interference & superposition, we can branch off into a few other sections:

• Stationary waves
• Two-source interference
• Single slit interference
• Diffraction grating

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⇐ Previous in Physics: Electromagnetic Spectrum
⇒ Next in Physics: Stationary Waves