1. Two spherical waves with the same amplitude, A, and wavelength, lamda, are spreading out from two point sources S1 and S2 along one side of a barrier. The two waves have the same phase at positions S1 and S2. The two waves are superimposed at a position P. If the two waves interfere constructively at P what is the relationship between the path length difference dx = d2 - d1 and the wavelength. If the two waves interfere destructively at P, what is the relationship between the path length difference and the wavelength.
2. What does it mean to say that two sources of waves are coherent, for instance, the waves in questions 2 above? If the sources in question 2 were two flashlights, would you observe interference at P? Explain.
