Problem 5.115

A plane light wave with wavelength \(\lambda=0.65\) \mum falls normally on a large glass plate whose opposite side has a ledge and an opaque strip of width \(a=0.30 \mathrm{~mm}\) (Fig. 5.23 ). A screen is placed at a distance \(b=110 \mathrm{~cm}\) 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 .