← all cardsTopic 11 · Wave Motion · The two graphs
v = fλ — and its derivation
● VERBATIM — examined word-for-wordSyllabus demands the deduction, not just the formula: in one period T the waveform advances one wavelength λ, so v = distance/time = λ/T; with f = 1/T, v = fλ. Applies to the wave profile, never to particles.
v = λ/T = fλWhat this actually means
The exam wants the logic, not the recall. In one period, each particle completes exactly one cycle, and in that same time the whole pattern slides forward exactly one wavelength.
Speed is distance over time: v = λ/T. Substitute f = 1/T and you have v = fλ. Two lines, both markable.
Note whose speed this is: the profile's. No particle ever moves at fλ.
Prove it — watch it be true
- Mark a crest, then STEP T/8 eight times: exactly one period has passed
- The crest has advanced exactly one wavelength
- Distance λ in time T: v = λ/T = fλ, derived on screen