A plane light wave with wave length λ = 0.65μm falls normally on a large glass plate whose opposite side has a ledge and an opaque strip of width a = 0.30 mm (Fig. 5.23). A screen is placed at a distance b = 110 cm from the plate. The height h of the ledge is such that the intensity of light at point 2 of the screen is the highest possible. Making use of Fig. 5.19, find the ratio of intensities at points 1 and 2.

y. 12