Interference of Waves

Wave interference is the phenomenon that occurs when two waves meet while traveling along the same medium.
The principle of superposition says  that the resulting wave is the sum of the two individual wave functions.

Two types of wave interference:

CONSTRUCTIVE INFERENCE:

a type of interference that occurs at any location along the medium where the two interfering waves have a displacement in the same direction. In other words, both waves have an upward displacement; consequently, the medium has an upward displacement that is greater than the displacement of the beginning waves.

For example, if the crests (or troughs) of two lwaves are in the same direction,

they combine together to create an amplified wave.

DESTRUCTIVE INFERENCE:  

a type of interference that occurs at any location along the medium where the two interfering waves have a displacement in the opposite direction. In other words, when two waves with
opposite displacements (one wave displaced up and the other down) meet at a given location, the upward pull of one wave is balanced (canceled or destroyed) by the downward pull of the other wave.

In the opposite scenario, where the crests of one wave are aligned with the troughs of another,

they cancel each other out.