Question

What do you mean by an optically denser and optically rarer medium?

Answer 1

1. Light travels faster in air or vacuum. It travels at a speed of $3\times {10}^{8}m/s$ in vacuum.
2. However the speed of light in other media is less than this.
3. The speed of light in water is $2.25\times {10}^{8}m/s$.
4. The speed of light in glass is $2\times {10}^{8}m/s$.
5. A medium in which light travels faster is called an optically rarer medium.
6. On the other hand, a medium in which light travels slower is called an optically denser medium.
7. Optically denser and rarer media are relative terms.
8. For example, the speed of light in water is less than the speed of light in air. Hence water is optically denser than air.
9. Similarly, the speed of light in water is more than the speed of light in glass. Hence water is optically rarer than glass.

Thus, a medium in which light travels faster is called an optically rarer medium and, the medium in which light travels slower is called an optically denser medium.