Sarthaks Test
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The light rays travelling from rarer to denser medium is given in the figure

1. Redraw the diagram and correct it

2. State the law relating i and r for retracted ray.

3. Velocity of light in water is 2.25 × 108 m/s, If angle of incidence is 30° calculate angle of refraction.

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2. Snells law:

The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media and for the given colour of light used. This constant is known as the refractive index of second medium w.r. t. the first medium.


If ‘i’ is the angle of incidence in the first medium and ‘r’ is the angle of refraction in the second medium, then by Snell’s law,

\(\frac{sin\,i}{sin\,r}=\frac{n_2}{n_1}\) = 1n2 = a constant

Where 1n2 is the refractive index of the second medium with respect to the first medium. If the first medium is air, then sin i/sin r is known as absolute refractive index of the second medium.

i.e, \(\frac{sin\,i}{sin\,r}\) = n

where ‘n’ is the refractive index of the second medium.

3.  n = \(\frac{sin\,i}{sin\,r}\) But n = \(\frac{c}{v}\)

\(\frac{c}{v}\) = \(\frac{sin\,i}{sin\,r}\)

\(\frac{3\times10^8}{2.25\times10^8}\) = \(\frac{sin\,30°}{sin\,r}\)

sin r = \(\frac{\frac{1}{2}\times 2.25\times10^8}{2.25\times10^8}\)

sin r = 0.375, r = 22°

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