Question

What is the speed of light in water?

Answer 1

We can find the speed of light in water from the Snell's Law:

$$\dfrac{v_2}{v_1}=\dfrac{n_1}{n_2},$$

here, $v_1=3\cdot10^8\ \dfrac{m}{s}$ is the speed of light in the air, $v_2$ is the speed of light in water, $n_1=1.0$ is the index of refraction of the air and $n_2=1.33$ is the index of refraction of water.

Then, from this formula we can find the speed of light in water:

$$v_2=\dfrac{v_1n_1}{n_2}=\dfrac{3\cdot10^8\ \dfrac{m}{s}\cdot 1.0}{1.33}=2.25\cdot10^8 \ \dfrac{m}{s}.$$

Answer:

$v_2=2.25\cdot10^8 \ \dfrac{m}{s}.$