Question

A visible spectrum is incident from the water to the air water interface at an angle $\theta$. $\theta$ is the critical angle for water to air interface when green light is incident.
Select the correct statement.

• A. The entire spectrum of visible light will come out of the water at various angles to the normal.
• B. The entire spectrum of visible light will come out of the water at an angle of ${90}^{\circ }$ to the normal.
• C. The spectrum of visible light whose frequency is less then that of green light will come out to the air medium.
• D. The spectrum of visible light whose frequency is more than that of green light will come out to the air medium.

Answer 1

The correct option is C The spectrum of visible light whose frequency is less then that of green light will come out to the air medium.

At critical angle, $\sin \theta$ =$\frac{1}{\mu }$
Also, the refractive index ($\mu$ of the medium depends on the wavelength of the light. is less for the greater wavelength (i.e. lesser frequency).
so $\theta$ will be more for a lesser frequency of light. Hence the spectrum of visible light whose frequency is less than that of green light will come out the air medium.