Ray Optics and Optical Instruments - Result Question 12
12. 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?
[2007]
(a) $2.4 \times 10^{8} m / s$
(b) $3.0 \times 10^{8} m / s$
(c) $1.2 \times 10^{8} m / s$
(d) $1.8 \times 10^{8} m / s$
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Answer:
Correct Answer: 12. (d)
Solution:
- (d)
From pythagorus theorem, Hypotenuse comes out to be $5 cm$.
Since, $\frac{1}{\mu}=\frac{\sin i}{\sin 90^{\circ}}$
$\mu=\frac{1}{\sin i}=\frac{5}{3}$
Speed, $v=\frac{c}{\mu}=\frac{3 \times 10^{8}}{5 / 3}=1.8 \times 10^{8} m / s$
