Two students discuss why a reflected pulse inverts when a wave travels from a faster…
PHYSICS · Single correct · A Level · Physics · Waves · Waves
Problem
Two students discuss why a reflected pulse inverts when a wave travels from a faster to a slower medium. Which statement provides the best explanation for the inversion?
(a) The boundary must remain momentarily at rest, so the reflected pulse flips to satisfy that constraint.
(b) Because the wave’s frequency changes at the boundary, it acquires a 180∘ phase shift that flips the pulse.
(c) Since the wavelength is shorter in the slower medium, the pulse must invert to match the new spatial pattern.
(d) The denser second medium pushes back with an equal and opposite force, forcing the reflected pulse to invert by Newton’s third law.