Chapter 37, Problem 37.75CP

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 shown in Figure P37.75. Slit S₁ is directly in line with S and at a distance of L = 1.20 in away from S, whereas S₂, is displaced a distance d to one side. The light is detected at point /Jon a second screen, equidistant from S₁ and S₂. When either slit S₁ or S₂ is open, equal light intensities are measured at point P. When both slits are open, the intensity is three times larger. Find the minimum possible value for the slit separation d.