Question

How does the critical angle depend on the refractive index?

Answer 1

Answer:

The value of the absolute refractive index of a material is inversely proportional to the wavelength of light used, (greater the wavelength of light used, lesser is the refractive index). By that logic, red light, which has the maximum speed in a medium shows the lowest refractive index for that medium. Violet light, which has minimum speed in a medium, shows the greatest refractive index for that medium.

Critical angle is defined as the angle of incidence in the optically denser medium when the corresponding angle of refraction in the optically rarer medium is 90 degrees.

Critical angle is inversely proportional to refractive index, (greater the refractive index of a medium, lesser is the critical angle). For example, the critical angle of glass is 42 degrees whereas critical angle of water, which is optically rarer than glass, is 49 degrees.

Similarly, as red light would show the lowest refractive index for a particular medium, its critical angle would be the greatest. The critical angle for violet light is the least as it has the highest refractive index.

Therefore, greater the wavelength of light used, greater is its critical angle.