Скачать или смотреть Edexcel A Level Physics - Superposition, Phase and Path Difference (Topic 5: Waves)

PHASE

Two points on a wave are said to be in phase if they are both at the same point on the wave - they will be separated by 0° or a multiple of 360º and have the same displacement and velocity. Points completely out of phase (in anti-phase) ware separated by 180º or multiples of 180º.

SUPERPOSITION

When two waves meet they are said to superpose. When waves superpose, the vector sum of their individual displacements will equal the resultant displacement of the wave. This is the principle of superposition. Waves will be the same before and after superposition. Superposition can only occur for waves of the same wave type.

Constructive Interference:

Constructive interference occurs when superposing waves have:
Displacements in the same direction (so displacements join to give an even longer displacement)
Similar amplitudes (the more similar their amplitude, the more obvious their interference)
Totally constructive interference occurs when waves are in phase

Destructive Interference:

Destructive interference occurs when superposing waves have:
Displacements in opposite directions (so displacements join to cancel each other out)
If the crest and trough are of the same magnitude they will cancel each other out
Totally destructive interference occurs when waves are in antiphase

PATH DIFFERENCE

Path difference is how much one wave has travelled relative to another.

When path difference is 0 or a whole number of wavelengths, constructive interference occurs and waves arrive at the same point in phase.
When path difference is an odd number of half wavelengths, destructive interference occurs and waves arrive at the same point in antiphase.