Destructive interference occurs when the maxima of two waves are 180 degrees out of phase: a positive displacement of one wave is cancelled exactly by a negative displacement of the other wave. The amplitude of the resulting wave is zero. ... In the image on the left, the phase difference is δ = π/2 or 90 degrees.

How does destructive interference affect the amplitude of a wave?

The amplitude is reduced to zero. Destructive interference means that two identical waves (same amplitude and wavelength) arrive in anti phase. In that case wherever wave 1 is at a peak wave 2 will be at a trough and vice versa.

Does the amplitude increase during constructive interference?

If we add these two waves together, point-by-point, we end up with a new wave that looks pretty much like the original waves but its amplitude is larger. This situation, where the resultant wave is bigger than either of the two original, is called constructive interference.