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NEET 2026
Exam
NEET
Year
2026
Subject
Physics
Chapter
Chapter

NEET 2026 · Physics · Chapter

An unpolarized beam of light travelling in a transparent dense...

An unpolarized beam of light travelling in a transparent dense medium of refractive index 3\sqrt{3} is incident on its interface with air at Brewster's angle. Which of the following statements is correct regarding the reflected and refracted light?

Options

  1. AThe reflected light is completely polarized and the angle of reflection is 60∘60^{\circ}.
  2. BThe transmitted light is completely polarized and the angle of refraction is 60∘60^{\circ}.
  3. CThe reflected light is completely polarized and the angle of refraction is 60∘60^{\circ}.
  4. DBoth reflected and transmitted light are partially polarized with an angle of 90∘90^{\circ} between them.

Correct answer

C. The reflected light is completely polarized and the angle of refraction is 60∘60^{\circ}.

Step-by-step solution

For light travelling from a dense medium of refractive index n1n_1 to a rarer medium of refractive index n2n_2, Brewster's angle θB\theta_B is given by:

tan⁡θB=n2n1\tan \theta_B = \dfrac{n_2}{n_1}

Given n1=3n_1 = \sqrt{3} and n2=1n_2 = 1 (air), we have:

tan⁡θB=13⇒θB=30∘\tan \theta_B = \dfrac{1}{\sqrt{3}} \Rightarrow \theta_B = 30^{\circ}

At Brewster's angle, the reflected light is completely polarized perpendicular to the plane of incidence.

The angle of incidence is i=θB=30∘i = \theta_B = 30^{\circ}. By the law of reflection, the angle of reflection is also 30∘30^{\circ}.

To find the angle of refraction rr, we use Snell's law:

n1sin⁡i=n2sin⁡rn_1 \sin i = n_2 \sin r

3sin⁡30∘=1×sin⁡r\sqrt{3} \sin 30^{\circ} = 1 \times \sin r

3(12)=sin⁡r⇒sin⁡r=32\sqrt{3} \left(\dfrac{1}{2}\right) = \sin r \Rightarrow \sin r = \dfrac{\sqrt{3}}{2}

⇒r=60∘\Rightarrow r = 60^{\circ}

Alternatively, at Brewster's angle, the reflected and refracted rays are mutually perpendicular, so i+r=90∘i + r = 90^{\circ}.

30∘+r=90∘⇒r=60∘30^{\circ} + r = 90^{\circ} \Rightarrow r = 60^{\circ}

Thus, the reflected light is completely polarized and the angle of refraction is 60∘60^{\circ}.

Answer: The reflected light is completely polarized and the angle of refraction is 60∘60^{\circ}.
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