Angle of the prism

A parallel beam of light is incident from air at an angle $$\alpha$$ on the side $$PQ$$ of a right angled triangular prism of refractive index $$n = \sqrt{2}$$. Light undergoes total internal reflection in the prism at the face PR when $$\alpha$$ has a minimum value of $$45^{\circ}$$. What is the angle $$\theta$$ of the prism in degrees?

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