A plate of thickness t made of a material of refractive index `mu` is placed in front of one of the slits in a double slit experiment. (a) Find the changes in he optical path due to introduction of the plate. (b) Wht 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 `lamda`. Neglect any absorption of light in the plate.

Explanation

Intensity at the centre will be zero if path difference
`=(lambda)/(2)" (or) "(mu-1)t= (lambda)/(2)" (or) "t= (lambda)/(2(mu-1))`.