Refraction on water

Refraction is the bending of a wave caused by a change in its speed as it moves from one medium to another.
This occurs because of the slow speed of light in dense materials.

Examples of phenomena caused by refraction

• When you place a bar in a cup with water, the bar looks bent.
• If you dip your feet in the water, it looks shorter than the original.
• The fish looks smaller when you take it out of the water.

But, why does the image of the fish in the water look smaller?

It’s not like that. Obviously, the image of the fish in the water appears larger than it should be. The reason for the illusion is that you are looking at this situation from the side. If you are in the eye position of this simulation, the fish in the water will appear larger than it should be.
Please see the viewing angle in the picture below. When the fish is in the water, they have a field of view of 36˚ and 26˚, respectively. However, without water, these fish are reduced to a field of view of 31˚ and 23˚, respectively. Therefore, fish appear larger in the water.