1.

**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.

**Explanation:**

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,

\(\frac{sin\,i}{sin\,r}=\frac{n_2}{n_1}\) = _{1}n_{2} = a constant

Where _{1}n_{2} 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**°**