Waves Rapid Review for AP Physics B & C

Review the following concepts if necessary:

• Transverse and Longitudinal Waves for AP Physics B & C
• Waves Interference for AP Physics B & C
• Standing Waves for AP Physics B & C
• Doppler Effect and Electromagnetic Waves for AP Physics B & C
• Single and Double Slits for AP Physics B & C
• Index of Refraction for AP Physics B & C
• Waves: Of Special Interest to Physics C Students

Rapid Review

• Waves can be either transverse or longitudinal. Transverse waves are up–down waves, like a sine curve. Longitudinal waves are push–pull waves, like a sound wave traveling through the air.
• When two waves cross paths, they can interfere either constructively or destructively. Constructive interference means that the peaks of the waves line up, so when the waves come together, they combine to make a wave with bigger amplitude than either individual wave. Destructive interference means that the peak of one wave lines up with the trough of the other, so when the waves come together, they cancel each other out.
• Standing waves occur when a wave in a confined space (for example, on a violin string or in a pipe) has just the right frequency so that it looks the same at all times. The simplest standing wave possible in a situation is called the fundamental frequency.
• The Doppler effect describes what happens when the source of a wave—such as a fire truck's siren—is moving relative to you. If the source moves toward you, you perceive the waves to have a higher frequency than they really do, and if the source moves away from you, you perceive the waves to have a lower frequency than they really do.
• All electromagnetic waves travel at a speed of 3 × 10⁸ m/s in a vacuum.
• The double-slit experiment demonstrates that light behaves like a wave.
• When light travels through anything other than a vacuum, it slows down, and its wavelength decreases. The amount by which light slows down as it passes through a medium (such as air or water) is related to that medium's index of refraction.
• Thin films can cause constructive or destructive interference, depending on the thickness of the film and the wavelength of the light. When solving problems with thin films, remember to watch out for phase changes.
• Maxwell's equations, which include among them Gauss's law, Faraday's law, and a modified version of Ampére's law, predict that accelerating charges produce electromagnetic waves that travel at a speed equal to 3 × 10⁸ m/s.