Slide 1
Two disturbances can overlap
When waves meet, their displacements can add. The combined disturbance may be larger or smaller than either wave alone.
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In the linear regime, each wave continues after the overlap rather than being permanently destroyed by the encounter. The visible combination at one moment is distinct from the later travelling disturbances.
Slide 2
Matching peaks reinforce
When similar waves arrive in step, their peaks align and the disturbance grows. This is constructive interference.
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Phase describes where a repeating wave is within its cycle. A consistent phase relationship produces stable interference patterns, which is why coherent sources are useful for controlled wave experiments.
Slide 3
Opposing phases reduce the result
A crest meeting an equal trough can produce zero displacement at that location. This is destructive interference, under the matching conditions.
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Cancellation at one position does not mean energy has vanished everywhere. In a spatial interference pattern, energy is redistributed, with stronger response in some regions and weaker response in others.
Slide 4
Path length sets the phase
Waves that travel different distances can arrive at different stages of their cycles. Changing path length therefore changes the interference pattern.
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A path difference of one wavelength returns identical-frequency waves to the same phase. A half-wavelength difference reverses their relative phase when they started together, explaining alternating bright and dark bands.
Slide 5
Interference becomes a measuring tool
Small path changes can move an interference pattern. Instruments use this sensitivity to detect changes too small for an ordinary ruler.
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The result depends on the wavelength and the surrounding medium as well as geometry. A change in refractive index can alter optical path length without moving a mirror, so environmental control is important.