Transparent wax of refractive index n=1.3 is deposited on top of a glass plate of width 1cm and refractive index n=1.5. The thickness of the wax is 0.01mm at one end of the plate and tapers uniformly to zero at the other end of the plate, which is defined to be at x=0. At this end the surface of the wax and of the glass form a small angle α. Light is incident on the plate from above, i.e. it goes through the wax, and is normal to the surface of the glass plate. Fringes are formed due to interference of light reflected from the top surface of the wax and from the glass.
i) Find the value of α.
ii) At what values of x do bright fringes occur if λ=520nm?
Thickness of wedge, d = x tan(α) ≈ αx
The Attempt at a Solution
i) tan(α)=0.01/10 = 1×10-3 radians
ii) I'm not sure whether bright fringes occur at xn = ((ρ+0.5)λ)/2nα) or xn = (ρλ/2nα)