← all cardsTopic 11 · Wave Motion · Phase & phase difference
The two phase formulas
● VERBATIM — examined word-for-wordSpace version (snapshot): Δφ = (Δx/λ) × 2π. Time version (y–t graphs): Δφ = (Δt/T) × 2π. If λ missing, get it from λ = v/f first. If Δφ > 2π, reduce into 0–2π and say so (9π/2 → π/2).
Δφ = (Δx/λ)·2π = (Δt/T)·2πWhat this actually means
Both formulas are one idea: what fraction of a full cycle separates the two things, times 2π. In space the fraction is Δx/λ; in time it is Δt/T.
If λ is not given, compute it from λ = v/f before anything else. If the answer exceeds 2π, subtract whole cycles and state that you did: 9π/2 becomes π/2.
Choose the version by graph type: separations on a y–x snapshot feed the space formula; offsets between y–t curves feed the time formula.
Prove it — watch it be true
- Pick P and Q with a known separation Δx
- Compute (Δx/λ) × 2π by hand
- Compare with the live Δφ readout — they match