The world above the water surface, as seen by a fish

[Fu-Kwun Hwang]

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There are 4 translations, select to view translated versionNederlands - Dutch(by mahjsa: 13)العربية - Arabic(by youmen: 12)English(by valerdragan: 12)English(by JoeBova: 12)
Higher number at the end means more translation been done.

or

When light propagates from one medium into another, its speed changes,
which causes the light to reflect and refract at the boundary.
 The index of refraction of water is 1.33 (4/3).
As light travels from water to air, it will bend away from the perpendicular to the surface.
When the incident angle is greater than 48 degrees, all the light is reflected back into the water (total internal reflection).

 As your pet goldfish in the aquarium looks up, it will see a reflected view of the sides and bottom of the aquarium beyond the 48 degree angle, while directly above, it sees a compressed view of the outside world.
 The refraction of light is responsible for many illusions:

• The shape of a thing 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.

This java applet lets you see the view as seen by your fish, looking up at you.. Pretty weird!

-*-

 Usage: The area is divided into two regions.
The light gray area is the air above the water surface. The green area is below the water surface.
A fish with two eyes is under the water surface.
 All the light from the world above the water surface that the fish can see enters the water through yellow region.
 The cyan colored block is an object above the water surface. The blue polygon is the imageof the block.
 The light path for each corner of the object is shown by the light gray lines.
 The yellow lines indicate where the object appears to be, to the fish.
As you will discover, the fish sees the world in very distorted form.

 Click one of the corners of the cyan block with the left mouse button to view light paths for that point.
 Click near the center of the block with the left mouse button and drag the mouse to move the object.
 Click the right bottom corner of the block with right mouse button and drag the mouse to change the size of the object.
 Move the object from LEFT TO RIGHT / UP AND DOWN/CHANGE ITS SIZE, and watch how the image changes.
Click at one of fish's eyes and drag the mouse button (left/right) to change the location of the eye.
 It's fun! Play with it! Think about it! Fish have to understand this! Enjoy the fun of physics. : ) Fill a glass with water and look at objects beneath the surface. Try it!

Registed user can get files related to this applet for offline access.
Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
If java program did not show up, please download and install latest Java RUN TIME

There are 4 translations, select to view translated versionNederlands - Dutch(by mahjsa: 13)العربية - Arabic(by youmen: 12)English(by valerdragan: 12)English(by JoeBova: 12)
Higher number at the end means more translation been done.

or

[AlbertF]

This is a quite an old and quirky Javascript program back from 2004.
-*-

[Fu-Kwun Hwang]

It is a java simulation. There is no javascript used in the above applet.
Java and Javascript are not the same (or similar at all).

[Bennigno]

Hi Prof Hwang,
  could you share the jar or xml source file of this java applet? I'd like to change the index of the water so that i can show the illusion position of what fish thinks. Or you could also add a negative checkbox into the current applet.
Many thanks!
CW

[lookang]

this is a older JDK1.0.2 simulations, they are not made using Easy Java Simulation (Ejs), thus they do not have *.xml source codes.

But you can download the standalone files, it think the source is inside but cannot be read by Ejs.

hope that helps
by the way,
you can search the entire forum and find that Prof Hwang has an Ejs version of a similar applet
An object under the water look differ! (Location and shape)
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=378.0

[Fu-Kwun Hwang]

The above applet was created with JDK 1.0.2
The java source code is available (attached file) if you want to modify it by yourself.

[leeyiren]

In the fish eye view from the water, why the image appears distorted? Any simple clear concise explanation? Thanks.

[lookang]

this is the same concept but the direction of light is opposite.

simply put, it is refraction of light hope it helps

[Fu-Kwun Hwang]

In the fish eye view from the water, why the image appears distorted? Any simple clear concise explanation? Thanks.

The first simulation was designed to help you understand why the image appears distored.
Please try to click the four corner of the object, the bending of the ray is different at different position.
The image was calculated from all points at the object. two rays emmitted from the the same point will refracted at different angle.  the interaction point of those two yellow line is the place where fish will see the image from that point.

You are welcomed to check out the following related applets.
An object under the water look differ! (Location and shape)
Where is the fish? (Refraction)

[koclup1580]

thank you..

[gulinekxchr]

Some of their own ideas, I do first under my experiment

[GolfBallJuggler]

How do I run this program offline...

[Fu-Kwun Hwang]

Did you find "get file for offline use button"?

Download file, unzip it and open index.html with your browser.

[tosraj]

I don't understand as to why light enters the water only through the yellow region. I understand that beyond the yellow region, the reflected bottom of the pool will be seen (green rays in figure below), but wouldn't it be a dim (less bright) compared to the light entering the water from the air (red rays in figure below) and reaching the fish? I assume a infinite or very large pond here (not an aquarium where light may enter from the sides too) so that the reflected light from the bottom of the pond is quite dim. Hence the fish must see the outside world superimposed with a dim reflection of the bottom of the pond. Where am I going wrong?

Thanks in advance for your reply and for your great post.

[susanrichard]

I was looking at your applet for the thin lens and really liked it. I am new to applets and
often it is possible to download them so that you can use them off line but I couldn't
work out what to do to download your applet.
I am a secondary teacher and would really like to show it to my students. Would I be
able to get a copy of it please. -*-

[Fu-Kwun Hwang]

Just click get file for offline use button to download jar file.

[susanrichard]

ok got it!! thanks for the answer. -*-