Interference & Doppler

Path difference decides loud/quiet; Doppler changes pitch.

Two-source interference

In-phase sources: nλ apart (or 0, 1λ, 2λ…) → constructive → loud/bright.
(n + ½)λ → destructive → quiet/dark.
Applies to sound, microwaves, light (young-type) identically.

ℹ

Doppler wording

Approaching: wavefronts compressed → wavelength shorter → frequency higher (pitch rises). Passing then receding: stretched → pitch falls. Draw circles offset forward.

Two coherent sources on the same frequency — strong and weak spots

Two Wi-Fi access points broadcasting on the SAME frequency act like coherent wave sources — where their path difference is a whole number of wavelengths, signals ADD (a strong spot); a half-integer difference gives a weak spot.

Practice for this standard covers the whole topic — flashcards and quiz.