# A green light is incident from the water to the air - water interface at the critical angle(u). Select the correct statement. Option 1) The entire spectrum of visible light will come out of the water at an angle of 900 to the normal.     Option 2) The spectrum of visible light whose frequency is less than that of green light will come out to the air medium. Option 3) The spectrum of visible light whose frequency is more than that of green light will come out to the air medium.   Option 4) The entire spectrum of visible light will come out of the water at various angles to the normal.

As we learnt in

Critical angle -

$\sin c$ = Refractive index of rarer medium / Refractive index of denser medium

- wherein

When angle of incidence of a travelling from a dence medium to rarer medium is greater than critical angle, no refraction occurs.

As $sin\theta=\frac{1}{\mu}$

Aslo refractive index (µ) of the medium depends on the wavelength of the light. µ is less for the greater wavelength. So $\theta$ will be move for lenser frequency of light.

Correct option is 3.

Option 1)

The entire spectrum of visible light will come out of the water at an angle of 900 to the normal.

This is an incorrect option.

Option 2)

The spectrum of visible light whose frequency is less than that of green light will come out to the air medium.

This is an incorrect option.

Option 3)

The spectrum of visible light whose frequency is more than that of green light will come out to the air medium.

This is an incorrect option.

Option 4)

The entire spectrum of visible light will come out of the water at various angles to the normal.

This is the correct option.

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