A green light is incident from the water to the air - water interface at the critical angle (θ). Select the correct statement. (a) The entire spectrum of visible light will come out of the water at an angle of 90° to the normal. (b) The spectrum of visible light whose frequency is less than that of green light will come out to the air medium. (c) The spectrum of visible light whose frequency is more than that of green light will come out to the air medium. (d) The entire spectrum of visible light will come out of the water at various angles to the normal.

Answer: (b). Light of lower frequency (towards red) has a smaller refractive index in water, so its critical angle is larger. Incident at green's critical angle θ, these colours have θ less than their critical angle, so they refract out into the air. Higher frequency colours have critical angle less than θ, so they are totally reflected. So the answer is (b).

A green light is incident from the water to the air - water interface… | JEE Main 2014

Q48JEE Main 2014Medium

Total Internal Reflection

A green light is incident from the water to the air - water interface at the critical angle $(\theta)$ . Select the correct statement.

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Answer: (b)

Light of lower frequency (towards red) has a smaller refractive index in water, so its critical angle is larger.
Incident at green's critical angle $\theta$ , these colours have $\theta$ less than their critical angle, so they refract out into the air.
Higher frequency colours have critical angle less than $\theta$ , so they are totally reflected.
So the answer is (b).

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