D $2-27$

$[5]$

va$.$ Fresnel bipriam is used to obtain fringes from a point source that is placed $1\mathrm{.}5$ m

from the screen, and the prism is midway between the source and the screen.

A Let the wavelength of the light be $500$ nm and the index of refraction of the glass n $=1\mathrm{.}5$ What is the prism angle if the separation of the fringes is $0\mathrm{.}5$ mm$?[5]$