JEE Main 2014 · 6 Apr · Shift 1 · Physics Q24

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PhysicsSingle correct+4 / -1Question 24 of 90

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

The entire spectrum of visible light will come out of the water at an angle of 90° to the normal.

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

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

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

Answer and worked solution

Official answer: B

Water's refractive index rises with frequency, so the critical angle $\sin\theta_c=\frac1n$ is larger for lower frequencies. The light meets the surface at green's critical angle.

Colours of lower frequency than green have a larger critical angle, so they are not totally reflected and emerge into air.
Higher-frequency colours are totally internally reflected.

Topics:Total internal reflection Prism and dispersion

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JEE Main 2014 · 6 Apr · Shift 1, Physics question 24