12–15% of the AP exam. 12 key topics. 4 common errors analyzed.
Unit 14 (Waves, Sound, and Physical Optics) extends the AP Physics 2 curriculum. Emphasize conceptual justification: FRQ scoring rubrics award points for physical reasoning stated in precise sentences.
These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.
Thin-film interference phase-shift errors — students misapply the rule that a phase shift of half a wavelength occurs only when reflecting from a medium with a higher index of refraction; omitting or incorrectly assigning phase shifts leads to reversing constructive and destructive interference conditions
Standing wave node/antinode confusion — misidentifying whether a pipe end (open vs. closed) corresponds to a node or antinode, leading to incorrect harmonic frequency sequences; closed ends are displacement nodes, open ends are displacement antinodes
Doppler effect formula sign errors — using the wrong sign in the numerator/denominator when the source and/or observer are moving toward vs. away from each other; a common shorthand ('top for observer, bottom for source') is applied without physical reasoning and breaks down for combined motion problems
Young's double-slit setup misidentification — confusing the slit separation d with the slit width (relevant for single-slit diffraction), or applying the small-angle approximation (sinθ ≈ tanθ ≈ y/L) outside its valid range without checking the geometry
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