Monochromatic light of wavelength 620 nm passes through a very narrow slit S and then strikes a screen in which are two parallel slits, S1 and S2, as in Figure P37.70. Slit S1 is directly in line with S and at a distance of L = 1.20 m away from S, whereas S2 is displaced a distance d to one side. The light is detected at point P on a second screen, equidistant from S1 and S2. When either one of the slits S1 and S2 is open, equal light intensities are measured at point P. When both are open, the intensity is three times larger. Find the minimum possible value for the slit separation d.

S1 So Viewing scree