Jengths = as long destructive interference results: 1aub: wavelengths; _ out = of phase and combine _ results when light paths differ by multiples of interference. Destructive = half-wavelength, whether the path lengths in Fig: 32.2b are the same, or differ by doesn't matter. Similarly, any other integer number of wavelengths. Thus, 1, 2, 3, or any Constructive interference results when light paths differ by an integer multiple of the wavelength. Crest meets trough: waves cancel. Crest meets crest: waves reinforce. In Qatar, taken by miles up. What's our ability to photos?
A half-wavelength path difference results in destructive interference. A full-wavelength path difference results in constructive interference before Feore 32i2. Two waves that start out in phase but travel different paths rejoin.