Glossary:  

Constructive interference – when two waves are in phase the combination of the two waves will be the sum of the waves at each point.

Destructive Interference – when two waves are not in phase the waves will cancel each other out.  (If the waves are 180 degrees out of phase, the waves will cancel each other out completely and there will be no net disturbance)

In phase – when the maximums and minimums of a wave coincide.

Out of phase – when the maximums and minimums of a wave do not coincide. 

Phase Velocity – velocity at which the transmitted wave moves, (not the velocity of the individual photons). 

Resonance – (wo) the natural or resonant frequency of an electron.  As the driving frequency gets closer to resonance the electron respo 

Superposition –