Question

Calculate the angle of emergence (e) of the ray of light incident normally on the face AC of a glass prism ABC of refractive index \(\sqrt 3\) . How will the angle of emergence change qualitatively, if the ray of light emerges from the prism into a liquid of refractive index 1.3 instead of air?

Answer 1

As light ray is incident normally on the face AC, it goes undeviated and strikes the face AB. At face AB, angle of incidence is \(30 ^\circ\).

Applying Snell's law at refracting surface AB

\(\frac{\sin 30^\circ}{\sin e} = \frac{n_a}{n_g}\)

or, \(\sin e = \frac{\sqrt 3}{1} \times \frac{1}{2}\)

or, \(\sin e = \sin 60 ^\circ\)

or, \(e = 60 ^\circ\)

If light ray emerges from prism into a liquid of refractive index 1.3 instead of air, then it will bend away from the normal by smaller extent as compared to air. So, angle of emergence will be less than \(60 ^\circ\).