A plane monochromatic light wave with wavelength `lambda` falls on the surface of a glass wedge whose faces from an angle `alpha lt lt 1`. The plane of incidence is perpendicualr to the edge, the angle of incidence is `theta_(1)`. Find the distance between the neighbouring fringe maxima on the screen placed at right angles to reflected light.

Explanation

We have usual equation fro maxima
`2h_(k) alpha sqrt(n^(2) - sin^(2) theta_(1)) = (k + (1)/(2)) lambda`
Hence `h_(k) =` distance of the fringe from top
`h_(k) alpha = d_(k) =` thickness of the film
Thus on the screen placed at right angles to the reflected light
`Deltax = (h_(k) - h_(k - 1)) cos theta_(1)`
`=(lambda cos theta_(1))/(2 alpha sqrt(n^(2) - sin^(2) theta_(1)))`