People with normal vision cannot focus their eyes underwater if they aren't wearing a face mask or goggles and there is water in contact with their eyes. Explain why not.

Explained

Explanation:

This happens because the water cancels the focusing effect of our eye lens. A drop of water makes a lens because of the different refractive indices of water and air.

When we are underwater with naked eyes, the front part of our eye lens does not have different refractive indices anymore ... both the inside lens and outside lens are essentially water (lens inside our eyes are water only surrounded by a membrane) ... hence, that part of the lens does not focus the light anymore. And thus, your eyes don't work well anymore. (It can only partly correct for this, by bending the lens more)

When we put swimming goggles on, we remove the water and again have air in front of our eye lenses, and they work normally now. Obviously, we have created an extra interface between water and air in front of our swimming goggles. However, this surface (the goggle) is flat. And thus it does not function as a lens but only as a window.