How energy travels without matter traveling with it. Mechanical waves, standing waves and resonance, sound and the Doppler effect, and the wave behavior of light itself — interference and diffraction — that geometric optics alone can't explain.
Six ways to master Unit 6 — pick whichever fits how you like to study.
Nine topics from the College Board CED, in order.
Unit 6 shifts from the ray-based picture of light in Unit 5 to a wave-based picture that applies to both mechanical waves (on strings, in air, in water) and light itself. You'll learn the basic vocabulary of waves — wavelength, frequency, amplitude — and see it applied to standing waves on instruments, the Doppler effect behind a siren's pitch shift, and ultimately to interference and diffraction, phenomena that only make sense if light behaves as a wave.
Young's double-slit experiment is the centerpiece of this unit's physical optics content — a beautifully simple experiment whose interference pattern provided some of the strongest historical evidence that light is a wave, not just a stream of rays. This unit makes up roughly 12–15% of the AP Physics 2 exam.
Note: the College Board's revised Course and Exam Description numbers the AP Physics 2 units 9–15, continuing from AP Physics 1's units 1–8 — so this unit appears there as Unit 14: Waves, Sound, and Physical Optics, with topics 14.1–14.9. We number it Unit 6 since it's the sixth unit of the Physics 2 course.