Section 3: Behavior of Waves

Reflection, refraction, and diffraction are all properties of waves.  Reflection occurs when a wave strikes an object and bounces off of it.  All types of waves can be reflected, including sound, water, and light waves.  The Law of Reflection states that a wave’s angle of incidence (i) always equals the angle of reflection (r).

Refraction is the bending of a wave caused by a change in speed as it moves from one medium to another.  For example, a pencil looks broken in water due to refraction.  When an object causes a wave to change direction and bend toward it, it’s called diffraction. Both refraction and diffraction cause waves to bend; however, refraction occurs when waves pass through an object, while diffraction occurs when waves pass around an object.

Interference occurs when two or more waves intersect simultaneously and at the same place. They then combine to form a new wave.  The two ways waves can combine are called constructive and destructive interference.  If the two waves add together, it’s called constructive interference.  However, suppose one wave has a positive amplitude, and one has a negative amplitude when they meet. In that case, the waves subtract from each other as they overlap, which makes it destructive interference.


  1. What types of waves can be reflected?
  2. Explain diffraction.
  3. Compare constructive interference to destructive interference.

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