Question

Is water optically denser than air?

Answer 1

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

Thus, water is optically denser than air.