Radius divided or multiplied by refractive index?

[Mr. Floyd]

First of all, sorry for bad english. Second of all sorry if such thread is already created, but I really need fast help.

Homework Statement

There's a lamp in the bottom of the lake. If you watch the lamp from the surface(out of the water) and your eyesight is crossed with the lake, you can see a bright circle. Radius of the circle is 10 meters. Refractive index of the water is 1,33. how deep in the water the lamp is.

Homework Equations

radius divided or multiplied by refractive index? that's the only idea i can come up with.

The Attempt at a Solution

10/1,33=7,52m
10*1,33=13,3m

well the task only has 2 numbers(10 and 1,33), so i think it has to to something with these.
What considers me is that there might be some "hidden numbers" in the text, that i can't read out at the moment.
please read this too:I understand that it very rude to come to this forum like that, and create a thread, what might already have answer, but I really need help.

 

[tiny-tim]

Welcome to PF!

Hi Mr. Floyd! Welcome to PF!

I understand that it very rude to come to this forum like that, and create a thread, what might already have answer, but I really need help.

No, that's exactly what you're supposed to do!

There's a lamp in the bottom of the lake. If you watch the lamp from the surface(out of the water) and your eyesight is crossed with the lake, you can see a bright circle. Radius of the circle is 10 meters. Refractive index of the water is 1,33. how deep in the water the lamp is.

I don't completely understand the question ,

but it looks as if it's about the angle of total internal reflection. ​

 

[Liquidxlax]

pictures always help in my opinion, and you use what Tiny-Tim stated