The ability of a medium to refract light is expressed in terms of its optical density. Optical density has a definite connotation. It is not the same…

(i) Refractive index of diamond \(\displaystyle =\frac{\text { Speed of light in vacuum }}{\text { Speed of light in diamond }}\) Speed of light in diamond \(\displaystyle =\frac{3 \times 10^{8} \mathrm{~m} / \mathrm{s}}{2.42}=1.23 \times 10^{8} \mathrm{~m} / \mathrm{s}\)

(ii) \(\displaystyle \angle \mathrm{r}\) in carbon disulphide \(\displaystyle <\angle \mathrm{r}\) in glass \(\displaystyle <\angle \mathrm{r}\) in water

(iii) (A)

The speed of light in water is more than the speed of light in glass. / Refractive index of glass is more than the refractive index of water.

(iii) (B) \[\begin{aligned} \mathrm{n}_{\text {glass }} & =\frac{3}{2} \\ \mathrm{n}_{\text {water }} & =\frac{4}{3} \\ \mathrm{~V}_{\text {glass }} & =2 \times 10^{8} \mathrm{~m} / \mathrm{s} \end{aligned} \] \[\begin{aligned} \mathrm{c}= & \mathrm{n}_{\text {glass }} \times \mathrm{v}_{\text {glass }} \\ & =\frac{3}{2} \times 2 \times 10^{8} \mathrm{~m} / \mathrm{s} \end{aligned} \] \[=3 \times 10^{8} \mathrm{~m} / \mathrm{s} \] \[\mathrm{v}_{\text {water }}=\frac{c}{n_{\text {water }}}=\frac{3 \times 10^{8} \mathrm{~m} / \mathrm{s}}{\dfrac{4}{3}} \] \[=\frac{9}{4} \times 10^{8} \mathrm{~m} / \mathrm{s} \text { or } 2.25 \times 10^{8} \mathrm{~m} / \mathrm{s} \]