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Question : 20
Total: 26
(i) A ray of light incident on face A B of an equilateral glass prism, shows minimum deviation of 30 ∘ . Calculate the speed of light through the prism.
(ii) Find the angle of incidence at faceA B so that the emergent ray grazes along the face AC.
(ii) Find the angle of incidence at face
Solution:
(i) Calculation of speed of light
(ii) Calculation of angle of incidence at face AB
(i)µ =
=
= √ 2
Also µ =
⇒ v =
m ∕ s
v = 2.122 × 10 8 m ∕ s
(ii)
At faceAC , let the angle of incidence be r 2 .
For grazing ray,e = 90 ∘
⇒ µ =
⇒ r 2 = s i n − 1 (
) = 45 ∘
Let angle of refraction at faceAB be r 1 .
Nowr 1 + r 2 = A
∴ r 1 = A − r 2 = 60 ∘ − 45 ∘ = 15 ∘
Let angle of incidence at this face bei
µ =
⇒ µ = √ 2 =
∴ i = s i n − 1 ( √ 2 ⋅ s i n 15 ∘ )
(ii) Calculation of angle of incidence at face AB
(i)
(ii)
At face
For grazing ray,
Let angle of refraction at face
Now
Let angle of incidence at this face be
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