the world above the water surface : fishes view

"the world above the water surface" viewed from fishes eyes

When light propagates through different medium, its wave speed changed,

which cause the light to reflect at the boundary.

The index of refraction of water is 1.33 (4/3.)

When light is traveling from water to air, it will bent away from the norm of the surface.

If the incident angle is greater than 48 degree,

all the light are reflected back into the water (total internal reflection).

So your pet goldfish in the bathtub looks up to see a reflected view

of the sides and bottom of the bathtub.

Directly above, it sees a compressed view of the outside world.

The refraction of light is responsible for many illusion:

What you see under the water surface is different from what it really is.

A submerged object appears to be nearer the surface than it actually is.

Would you like to know what is the view from the fish under the water looking at you?

This java applet let you feel it :

The world above the water surface viewed under the water. Have fun!

Usage: The whole area is divided into two region:

the light Gray area is above the water surface:

The cyan colored block is an object above the water surface.

The blue polygon is the image of the block.

The light path for one corner of the object is shown with light Gray lines.

The yellow lines indicate what the object appear to be.

Click one of the corner of the cyan block with left mouse button

to view light paths for that point.

Click near the center of the block with left mouse button

and drag the mouse to move the object.

Try to move the object from LEFT TO RIGHT / UP AND DOWN,

and watch how the image changes.

You will know the fish's view is so different from what we see.

Click the right bottom corner of the block with right mouse button

and drag the mouse to change the size of the object.

The green area is under the water surface:

A fish with two yes is under the water surface.

Click at one of fish's eye and drag the mouse button (left/right)

to change the location of the eye.

All the light from the world above the water surface enter the water

through yellow region.

Is it fun! Play with it! Think about it! Enjoy the fun of physics. : )

Fill a cup of glass with water and look at objects behind the glass. Try it!

Your suggestions are highly appreciated! Please click hwang@phy03.phy.ntnu.edu.tw

Author：Fu-Kwun Hwang, Dept. of physics, National Taiwan Normal University