# Why fish under water see a circle surrounded by darkness

1. Oct 22, 2012

### Drezzan

A fish looking straight up to the surface of a pond receives a cone of light filled with images. This bright field is surrounded by darkness. Explain what is happening and compute the cone angle.

No given data but $n_w=1.33$

No give equations but I anticipate Snell's law and maybe the critical angle equations will come into play.

My attempts were to explain this by the light rays being bent in a way that the higher $\theta_i$ completely miss the fish eye. However that would not create the dark halo effect the problem states. I have looked for an answer using total internal reflection but that requires the light to be passing from a dense medium to a less dense. Total external reflection also has the stipulation the that the frequency of the light must be much greater than the resonant frequency of the atoms, and this would cause no light transmitted correct? Please help me understand this question a bit better. Thank you !!

Last edited: Oct 22, 2012
2. Oct 22, 2012

### Antiphon

"I have looked for an answer using total internal reflection but that requires the light to be passing from a dense medium to a less dense"

So what would this look like to you if you were underwater? Assume that there is only darkness from the direction of the water and all the light is coming from above the water.

3. Oct 22, 2012

### marty1

outside of that cone, there is reflection only of the "darkness" from below.

4. Oct 22, 2012

### Drezzan

Oh wow thank you I guess I was over thinking this.