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Question

Physics Question on Ray optics and optical instruments

A wide slab consisting of two media of refractive indices n1n_{1} and n2n_{2} is placed in air as shown in the figure. A ray of light is incident from medium n1n _{1} to n2n _{2} at an angle θ\theta, where sinθ\sin \theta is slightly larger than 1n1\frac1 { n _{1}}. Take refractive index of air as 11.Which of the following statement(s) is(are) correct?
A wide slab consisting of two media of refractive indices 𝑛1 and 𝑛2 is placed in air

A

The light ray enters air if n2=n1n_{2}=n_{1}

B

The light ray is finally reflected back into the medium of refractive index n1n _{1} if n2<n1n _{2}< n _{1}

C

The light ray is finally reflected back into the medium of refractive index n1n_{1} if n2>n1n_{2}>n_{1}

D

The light ray is reflected back into the medium of refractive index n1n_{1} if n2=1n_{2}=1

Answer

The light ray is finally reflected back into the medium of refractive index n1n _{1} if n2<n1n _{2}< n _{1}

Explanation

Solution

sin(θ)>1n1\sin(\theta) > \frac{1}{n_1} … (i)

And n1sin(θ)=1×sin(r)n_1 \sin(\theta) = 1 \times \sin(r) … (ii)

sinr>1⇒ sinr > 1

refraction into air is not possible
Therefore correct options are :
(B) The light ray is finally reflected back into the medium of refractive index 𝑛1 if n2<n1n_2 < n_1
(C) The light ray is finally reflected back into the medium of refractive index 𝑛1 if 𝑛2>𝑛1𝑛_2 > 𝑛_1
(D) The light ray is reflected back into the medium of refractive index 𝑛1 if 𝑛2 = 1