Question

A plate of thickness t made of a material of refractive index μ is placed in front of one of the slits in a double slit experiment. (a) Find the change in the optical path due to introduction of the plate. (b) What should be the minimum thickness t which will make the intensity at the centre of the fringe pattern zero ? Wavelength of the light used is λ. Neglect any absorption of light in the plate.

Answer 1

a) Change in the optical path = ​μt – t = (μ – 1)t
b) To have a dark fringe at the centre the pattern should shift by one half of a fringe.