Chapter 35, Problem 90P

In Fig. 35-54, two isotropic point sources S₁ and S₂ emit light at wavelength λ = 400 nm. Source S₁ is located at y = 640 nm; source S₂ is located at y = –640 nm. At point P₁ (at x = 720 nm), the wave from S₂ arrives ahead of the wave from S₁ by a phase difference of 0.600Π rad. (a) What multiple of λ gives the phase difference between the waves from the two sources as the waves arrive at point P₂, which is located at y = 720 nm? (The figure is not drawn to scale.) (b) If the waves arrive at P₂ with equal amplitudes, is the interference there fully constructive, fully destructive, intermediate but closer to fully constructive, or intermediate but closer to fully destructive?

Figure 35-54 Problem 90.