A small coin is resting on the bottom of a beaker filled with a liquid. A ray of light from the coin travels upto the surface of the liquid and moves along its surface (see figure). [AIPMT (S) 2007] |
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How fast is the light travelling in the liquid? |
A) \[1.8\times {{10}^{8}}m/s\]
B) \[2.4\times {{10}^{8}}m/s\]
C) \[3.0\times {{10}^{8}}m/s\]
D) \[1.2\times {{10}^{8}}m/s\]
Correct Answer: A
Solution :
Key Idea : Critical angle is the angle of incidence in denser medium for which the angle of refraction in rarer medium is ![]() |
As shown in figure, a light ray from the coin will not emerge out of liquid, if ![]() |
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Therefore, minimum radius R corresponds to ![]() ![]() |
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or ![]() |
or ![]() |
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Given, ![]() |
Hence, ![]() |
or ![]() ![]() |
But ![]() ![]() |
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