What characterizes constructive interference in waves?

Constructive interference occurs when two or more waves superimpose to form a wave of greater amplitude. For constructive interference to take place, the waves must be in phase, which means that the peaks (and troughs) of the waves align with one another.

The condition for constructive interference is that the difference in path length between the waves should equal an integer multiple of the wavelength. This is critical because when the path length difference is a multiple of the wavelength, the waves have traveled the same distance — or a coordinated distance that is a whole number of wavelengths — ensuring that their crests and troughs match up perfectly. This alignment enhances the resultant wave's amplitude, illustrating constructive interference.

This understanding sets apart other potential choices – significant differences in path length that are not multiples of the wavelength would lead to destructive interference or other forms of wave behavior where the waves do not reinforce each other effectively. Thus, the correct characterization of constructive interference is reflected in the choice that states the difference in path length is indeed a multiple of the wavelength.