Constructive and Destructive Interference

Consider the phase of the waves being added.

The sum of waves in the same medium leads to:

1. constructive interference: the two waves are in phase and their sum leads to an inrease of amplitude
2. destructive interference: the two waves are out of phase and the sum leads to a decrease in the overall amplitude.

Interference

Figure: Superposition of Waves, animation courtesy of Dr. Dan Russell, Penn State University.