Let’s discuss four ways you can affect a wave. Reflection is the bouncing of a wave off of a barrier. The law of reflection states that the angle of incidence of a wave is equal to the angle of reflection of the wave as measured from a line normal (perpendicular) to the barrier. This simply means that the wave will bounce off at the same angle at which it came in.
Refraction is the bending of a wave due to a change in medium. A water wave moving from deep water to shallow water will bend its path, slow down, and shorten its wavelength.
The speed of the wave and its wavelength always change when a wave undergoes refraction, but its frequency does not change. According to the equation v = f λ, a slower speed means having a shorter wavelength, and a higher speed means having a longer wavelength.
Diffraction is the bending of a wave around a barrier, such as water waves bending around a rock in a stream, or sound waves bending around the corner of a building. When water waves pass through a narrow opening, the sides of the waves drag on the walls of the opening, causing these parts of the wave to lag behind the center of the wave and creating a semicircular wave pattern, as shown in the figure below.
When two waves are traveling in the same medium at the same time, they interfere with each other. For example, consider two waves moving toward each other in the same rope. If the waves are moving on the same side of the rope, they build on each other and create a larger amplitude wave when they occupy the same space at the same time. This is called constructive interference, and the large wave produced at that instant is called an antinode.
We say that the waves are in phase when they interfere constructively. After the waves pass through each other, they continue moving as if they never interfered.
If two waves of equal amplitude approach each other on opposite sides of the rope, they interfere destructively: that is, the waves destroy each other for the instant they are occupying the same point on the rope and a node is created at that point. A node is a point of no displacement, in this case resulting in a flat rope.
We say that the waves are out of phase when they interfere destructively. Once again, after the waves pass through each other, they continue moving as if they never interfered.