State the laws of refraction of light. If the speed of light in vacuum is $3 \times 10^{8} \text{ ms}^{-1},$ find the speed of light in a medium of absolute refractive index 1.5.
CBSE DELHI - SET 2 2014
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Laws of refraction of light:
- The incident, the refracted ray and normal at the point of incidence, all lie in the same plane.
- The second law of refraction is called snell’s law of refraction. According to snell’s law, “The ratio of sine of angle of incidence to the sine of angle of refraction is a constant for a given pair of mediums”.
$\frac{\text{Speed of light in vaccum}}{\text{Speed of light in a medium}} = \text{Refractive index of the medium}$
$\Rightarrow \frac{3 \times 10^{8} \text{m/s}}{x} = 1.5$
$\Rightarrow x = \frac{3 \times 10^{8} }{1.5} = 2 \times 10^{8} \text{ m/s}$
$\therefore \text{Speed of light in the medium} = 2 \times10^{8} \text{ m/s}$
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