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A small coin is resting on the bottom of a beaker filled with liquid. A ray of light from the coin travels upto the surface of the liquid and moves along its surface. How fast is the light travelling in the liquid?

1. 1.33
2. 1.40
3. 1.50
4. 3.00

Correct answer: 1.50

Solution

The light ray traveling along the surface indicates that it is at the critical angle. Using Snell's law and the refractive index of the liquid, the speed of light in the liquid can be calculated as v = c/n. Here, n = 1.50, so v = 3.00 x 10^8 / 1.50 = 2.00 x 10^8 m/s. Thus, the refractive index is 1.50.

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