Boundary crossing — f is sacred
● VERBATIM — examined word-for-wordEntering a new medium: frequency unchanged (set by the source), speed changes, so λ = v/f scales with v. With amplitude info, I ∝ A² finishes the row: v and A both halved → (0.25I, f, 0.50λ). Writing "frequency halves" = instant lost mark.
What this actually means
Frequency counts oscillations arriving per second, and it is set by the source. The boundary cannot swallow cycles or invent them, so f is identical on both sides.
Speed changes with the medium, so λ = v/f stretches or shrinks in proportion to v. Slower medium, shorter wavelength.
If amplitude information is given, finish with I ∝ A². State f constant FIRST, then one quantity per sentence. Writing 'frequency halves' anywhere is an instant lost mark.
Writing that frequency changes at a boundary — only v and λ change.
Prove it — watch it be true
- Watch the wave cross the boundary: the two f counters tick in step
- The wavelength visibly shrinks on the slow side
- Same beat, shorter steps: λ follows v, f follows the source