According to _____ each point on a wave front is a source of secondary wave fronts. This principles applies to wave fronts that are both _____ and _____ in shape.

The direction of waves moving in two or three dimensions is shown by diagrams. The ray that reaches a barrier is called the _____ ray. The ray that moves back from the barrier is called the _____ ray. The direction of the barrier is shown by a line drawn at a(n) _____ angle to the barrier. This line is called the _____. The angle between the _____ ray and the _____ is called angle of incidence. The angle between the _____ ray and the _____ is called the angle of reflection. The law of _____ states that the angle of incidence equals the angle of reflection.

In water waves, the velocity is _____ in shallower water. If the incident ray is parallel to the normal, there is a change in the velocity and _____ of the wave. If the incident ray is not parallel to normal, there is a change in velocity, wavelength, and _____ of the wave. The change in _____ of a wave at the boundary between two media is called refraction.

When plane waves reach a small opening in a barrier, they form _____ waves that spread out behind opening. This spreading of waves is called _____. The smaller the _____ in comparison to the size of the barrier, the _____ the diffraction. When there are two openings in a barrier, two sets of in-phase and coherent waves are produced. When these new waves interfere with each other, constructive interference produces large waves, and _____ interference produces a line of nodes. The amount of interference can be increased by either _____ the frequency at which the point sources are vibrating or by moving the point sources _____ apart.