A parallel beam of light is made incident as shown on the flat diametric plane of a transparent semi-circular thin sheet of thickness $$t$$ with $$t \ll R$$ and refractive index $$\mu=\sqrt2$$ at an angle of $$45^\circ$$. As a result of refraction, the light enters the semi-circular sheet and comes out at its curved surface. Here $$\theta$$ is the angle between the vertical diameter $$AB$$ and the concerned radius of the semicircular sheet of radius $$R$$.