Does a swimmer underwater observe the same color or a different color for this light?

1. a swimmer underwater observes a different color because the wavelength changes.
2. it is not possible to know what a swimmer underwater will observe.
3. a swimmer underwater observes a the same color because the wavelength does not change.
4. a swimmer underwater observes the same color because the frequency does not change.
5. a swimmer underwater observes a different color because the frequency changes.

Explanation:

When a swimmer is underwater and a light pasess from air to water, there is a change in the medium and its index of refraction, hence the light is refracted. This means it changes its direction.

Nevertheless, in this process the refracted ray of light does not change its frequency , because frequency is:

Where is the period of the wave and this remains unchanged, hence the frequency, as well.

So, as the frequency does not change and the color of light depends on frequency, the color of the light remains the same.

heat the gas and measure the pressure