What is going on?
The inverted moving fish (virtual image) is what the observer (fish on the left) will see underwater.
When the moving fish is away from the observer,
light emitter from the moving fish will be totally reflected at the water-air interface.
So the water-air interface acting like a mirror.
When the distance is too short for the total internal reflection to occurs,
the virtual image above the water vanished.
You can click and drag the observer left/right to change its location.
More information will be shown when you drag the observer (fish).
Why does a fish appear to be closer to the surface of water than it really is?
The following java applet let you find out the answer,
and learn the physics of refraction, and total internal reflection.
A scanning eye represent the observer. You can click on it and drag it to any position you like.
The whole screen will be clear when you drag the scanning eye.
You can draw any pattern you like, and the java program will draw the virtual image of it.
( If the virtual can be formed due to refraction or total internal reflection)
When you draw in the water region,
the region where the total internal reflection is possible, will be shown.
If you click the right mouse button, it will show you many light rays emitted.
(including refraction rays and total internal reflection rays)
Right click the mouse button twice is another way to clear the screen.
You can draw any thing within the animation region,
for example: the object shown in the above image.
Light emitted from the object is refracted at the water and air interface.
The observer trace back those refracted light to find the image of the object.
The image appear closer to the water surface and its shape is different from the object.
How to determine the location of the image (yellow dot) ?
The world viewed under water is different from what we view it above the water surface.
Drag the observer (eye) under the water and find out more interesting phenomena.
Author¡GFu-Kwun Hwang, Dept. of physics, National Taiwan Normal UniversityLast modified : More physics related java applets