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Light Reflection and Refraction
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15/08/2021 1:44 pm
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(a) State and explain the laws of refraction of light with the help of a labelled diagram.
(b) What is meant by the refractive index of a substance?
(c) Light travels through air at 300 million ms-1. On entering water it slows down to 225 million ms-1. Calculate the refractive index of water.
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15/08/2021 1:47 pm
(a) Laws of refraction:
First law: According to the first law of refraction, the incident ray, the refracted ray and the normal at the point of incidence, all lie in the same plane.
Second law: According to the second law of refraction, the ratio of the sine of angle of incidence to the sine of angle of refraction is constant for a given pair of media.
(b) Refractive index of substance: The ratio of speed of light in vacuum to the speed of light in a medium, is called the refractive index of that medium.
(c) Speed of light in air = 300 million m/sec
Speed of light in water = 225 million m/sec
We know that
Refractive index of water = \(\frac{speed\;of\;light\;in\;air}{Speed\;of\;light\;in\;water}\)
Refractive index of water = \(\frac{300 \;million \;m/sec}{225 \;million \;m/sec}\)
= 1.33