Phase difference, Δφ
● VERBATIM — examined word-for-wordA measure, in angular form, of how much one particle/wave is out of step with another — the fraction of a cycle one is ahead of or behind the other. Quote in the range 0 ≤ Δφ < 2π. Only meaningful for the same frequency.
What this actually means
Δφ measures how far ahead or behind one oscillation is compared with another, as a fraction of a cycle written as an angle. One wavelength apart is a full cycle, 2π; half a wavelength is π.
Always reduce into the range 0 to 2π. An answer of 9π/2 should be quoted as π/2, with a line saying you reduced it.
It only means anything for two oscillations of the same frequency. Different frequencies drift past each other, so their phase difference changes constantly; if asked, say exactly that.
Quoting a phase difference between waves of different frequencies — it is meaningless because it keeps changing.
Prove it — watch it be true
- Pick particles P and Q and read the live Δφ
- Drag them further apart: Δφ grows with separation
- Snap to λ: Δφ wraps back to 0 — a full cycle of separation