A screen is at a distance D = 80 cm from a diaphragm having two narrow slits S1 and S2 which are d = 2 mm apart. Slit S1 is covered by a transparent sheet of thickness t1 = 2.5 µm and S2 by another sheet of thickness t2 = 1.25 µm as shown in figure. Both sheets are made of same material having refractive index µ = 1.40. Water is filled in space between diaphragm and screen.

A monodichromatic light beam of wavelength λ = 5000 Å is incident normally on the diaphragm. Assuming intensity of beam to be uniform and slits of equal width, calculate ratio of intensity at C to maximum intensity of interference pattern obtained on the screen, where C is foot of perpendicular bisector of S1S2. (Refractive index of water, µw = 4/3)