In Figure two isotropic point sources S1 and S2 emit light at wavelength ? = 400 nm. Source S1 is located at y = 640 nm; source S2 is located at y = ?? 640 nm. At point P1 (at x = 120 nm), the wave from S2 arrives ahead of the wave from S1 by a phase difference of 0.600? rad.(a) What multiple of ? 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?

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