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NEET 2014
Exam
NEET
Year
2014
Subject
Physics
Chapter
Ray Optics

NEET 2014 · Physics · Ray Optics

The angle of a prism is ‘ A ’. One of its refracting...

The angle of a prism is ‘ AA ’. One of its refracting surfaces is silvered. Light rays falling at an angle of incidence 2A2A on the first surface returns back through the same path after suffering reflection at the silvered surface. The refractive index μ,\mu, of the prism is:The angle of a prism is ‘ A ’. One of its refracting surfaces is silvered. Light rays falling at an angle

Options

  1. A2sinA2sin A
  2. B2cosA2cos A
  3. C12cosA\dfrac{1}{2}cos A
  4. DtanAtan A

Correct answer

B. 2cosA2cos A

Step-by-step solution

The angle of a prism is ‘ A ’. One of its refracting surfaces is silvered. Light rays falling at an angle
To retrace its path light rays should fall normally on the reflecting surface. So
r2=0{r}_{2} = 0
⇒r1=A−r2⇒r1=A⇒ {r}_{1} = A - {r}_{2} ⇒ {r}_{1} = A
Now applying snell rule between incident ray and refracted ray.
\left(1\right)\sin \left(2A\right) = nsin \left(A\right) ⇒ 2sin Acos A = nsin A<br/><br />⇒ n = 2cos A
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