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InterferencePhase

Constructive and destructive interference can be explained in terms of phase and path difference. Interference patterns can be calculated using wavelength, grating spacing and angle of maxima.

Part of PhysicsParticles and waves

Phase

Constructive interference

If two waves coincide with peaks and troughs matching they are said to be in phase.

Two waves coinciding with peaks and troughs to match.

If two periodic waves of similar frequency coincide in phase the waves superimpose their wave energy to produce a wave of double the amplitude. This is constructive interference.

Two waves coinciding with peaks and troughs to match and + symbol between them. Below the two waves is wave with the peak and trough heights intensified by two. Between the two peaks is an = symbol.

Destructive interference

If two waves coincide with peaks of one meeting troughts of the other they are said to be out of phase.

If two waves are exactly out of phase they will interfere destructively to produce zero amplitude.

Two waves out of phase peak close together, top wave peak and bottom wave trough very far apart. + symbol between waves. Right hand side has = symbol and then a flat line.
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When does interference occur?

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