13.3 Wave Interaction: Superposition and Interference

• Most waves appear complex because they result from two or more simple waves that combine as they come together at the same place at the same time—a phenomenon called superposition.
• The two special cases of superposition that produce the simplest results are pure constructive interference and pure destructive interference.
• Pure constructive interference occurs when two identical waves arrive at the same point exactly in phase.
• When waves are exactly in phase, the crests of the two waves are precisely aligned, as are the troughs.
• two identical waves that arrive exactly out of phase—that is, precisely aligned crest to trough—producing pure destructive interference.
• Because the disturbances are in opposite directions for this superposition, the resulting amplitude is zero for pure destructive interference; that is, the waves completely cancel out each other.
• Sometimes waves do not seem to move and they appear to just stand in place, vibrating. Such waves are called standing waves and are formed by the superposition of two or more waves moving in opposite directions.
• The nodes are the points where the string does not move; more generally, the nodes are the points where the wave disturbance is zero in a standing wave.
• The antinode is the location of maximum amplitude in standing waves.
• As we saw in the case of standing waves on the strings of a musical instrument, reflection is the change in direction of a wave when it bounces off a barrier, such as a fixed end.
• As it is reflected, the wave experiences an inversion, which means that it flips vertically.
• At the boundary between media, waves experience refraction—they change their path of propagation.