5. Consider a dielectric slab having a thickness d=10mm and index of refraction n =1.50. Let the medium above and below the slab be air, in which = =1. Let the wavelength be 10 mm (equal to the thickness of the waveguide). a) What is the critical angle for the slab waveguide? b) Solve the Equation below graphically tan nd sine m n cos20-n 2 m n sine (which is the solution of slab waveguide propagating rays -given in class) to show that there are three angles of incidence which satisfy this equation. c) What happens to the number of angles as the wavelength is decreased?