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JEE Advanced 2019 Paper 2
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© examsnet.com
Question : 13
Total: 54
A monochromatic light is incident from air on a refracting surface of a prism of angle 75° and refractive index
n
0
=
√
3
other refracting surface of the prism is coated by a thin film of material of refractive index n as shown in figure. The light suffers total internal reflection at the coated prism surface for an incidence angle of
θ
≤
60
°
The value of
n
2
is
Your Answer:
Validate
Solution:
For TIR at other face.
sin
θ
c
′
=
n
√
3
Snell law at first surface
sin
θ
=
√
3
sin
(
75
−
θ
c
′
)
⇒
For
θ
=
60
∘
∴
√
3
2
=
√
3
sin
(
75
−
θ
c
′
)
⇒
sin
(
75
−
θ
c
′
)
=
1
2
∴
θ
c
′
=
45
∘
⇒
1
√
2
=
n
√
3
⇒
n
=
√
3
2
∴
n
2
=
3
2
=
1.5
© examsnet.com
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