Physics, asked by abc523, 11 months ago

A 2.5 cm cube is constructed of a material whose refractive index is 1.65. Calculate the least radius of an opaque circular disc, which must be placed centrally over each face of the cube, so that a small air bubble at its centre shall be invisible from an external point
(A) 0.95 cm
(B) 0.59 cm
(C) 1.25 cm
(D) 0.75 cm
Answer is A. Please explain it.. ​

Answers

Answered by Anonymous
14

Solution :

Given:

Height (cube) = 2.5 cm

Refractive index = 1.65

So,

\implies 1.65 sin r = 1

\implies sin r = 1 / 1.65

Now:

\implies \sf{R = \frac{2.5}{2}\:cos\:r}

\implies \sf{R=\frac{2.5}{2} \:\sqrt{1 - \frac{1}{(1.65) ^{2} } }}

\implies \sf{R=1.25\:\sqrt{1 - \frac{1}{2.7225}}}

\implies \sf{R=1.25\:\sqrt{1 - 0.3673}}

\implies \sf{R=1.25\:\sqrt{0.6327}}

\implies \sf{R=0.95 \: cm}

Hence:

Correct option: (A) 0.95 cm

Therefore:

The least radius of an opaque circular disc, which must be placed centrally over each face of the cube, so that a small air bubble at its centre shall be invisible from an external point is 0.95 cm.

_______________

Answered by: Niki Swar, Goa❤️

Attachments:
Answered by Anonymous
5

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