Answer
In constructive interference, 2 wave peaks reach a point at the same time, and superpose. They cause a net effect that is larger than either of the individual waves. Constructive interference also occurs when 2 wave troughs reach a point at the same time.
In destructive interference, a wave peak and a wave trough reach a point at the same time, and superpose. Their opposite displacements cause a diminished effect that is smaller than either of the individual waves.
Work Step by Step
This is discussed on page 363.
