For a symmetric (equilateral) prism, the prism formula can be written as

For a ray of light, the critical angle is minimum, when it travels from

Critical angle of light passing from glass to air is minimum for wavelength of

A vessel is filled with two different liquids which do not mix. One is 40 cm deep and has refractive index 1.6 and other is 30 cm deep and has refractive index $1 \cdot 5$. The apparent depth of vessel when viewed normally is