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CIE A Level Physics復習筆記8.2.2 Interference & Coherence

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年8月16日下午3:27

Interference occurs when waves?overlap?and their resultant displacement is the?sum of the displacement of each wave
This result is based on the principle of superposition and the resultant waves may be smaller or larger than either of the two individual waves
Interference of two waves can either be:
- In?phase, causing?constructive interference.?The peaks and troughs line up on both waves. The resultant wave has double the amplitude
- In?anti-phase, causing?destructive interference.?The peaks on one wave line up with the troughs of the other. The resultant wave has no amplitude

Constructive and destructive, downloadable AS & A Level Physics revision notes

Waves in superposition can undergo constructive or destructive interference

At points where the two waves are neither in phase nor in antiphase, the resultant amplitude is somewhere in between the two extremes
Waves are?coherent?if they have the same?frequency?and?constant phase difference

8.2.2.1-Coherent-v-non-coherent

Coherent v non-coherent wave. The abrupt change in phase creates an inconsistent phase difference

Coherence is vital in order to produce an observable interference pattern
Laser light is an example of a coherent light source, whereas filament lamps produce incoherent light waves

The diagram shows the interferences of coherent waves from two point sources. WE-Interference-and-coherence-question-image-1

Which row in the table correctly identifies the type of interference at points?X,?Y?and?Z. WE-Interference-and-coherence-question-image-2

ANSWER:?B

At point X:
- Both peaks of the waves are overlapping. This is?constructive?interference and rules out options C and D
At point Y:
- Both troughs are overlapping and so?constructive?interference occurs there
At point Z:
- A peak of one of the waves meets the trough of the other. This is?destructive?interference (Row B)