Physics - Geometrical Optics Question with Solution | TestHub

The beam enters the vertical face normally, so it travels undeviated and strikes the hypotenuse at 45°.

Critical angles: $\sin c=\frac{1}{\mu }$

$c_{red}={\sin }^{-1}\frac{1}{1.39}\approx 46^{\circ },c_{green}={\sin }^{-1}\frac{1}{1.44}\approx 43.9^{\circ },c_{blue}={\sin }^{-1}\frac{1}{1.47}\approx 42.8^{\circ }$

Incidence 45° exceeds c for green and blue, so they undergo total internal reflection; 45° < c for red, so red refracts out.

Hence the prism separates (part of) the red colour from the green and blue colours. Hence (A).