Light in Underwater Pool Refraction Problem

[JSGandora]

Homework Statement

A small underwater pool light is 1 meter below the surface of a swimming pool. What is the radius of the circle of light on the surface, from which light emerges from the water?

Homework Equations

Snell's Law
Fermat's Principle

The Attempt at a Solution

I have no idea about how to approach the first part because we're not given the radius of the light.

 

[ehild]

A small underwater pool light is 1 meter below the surface of a swimming pool. I also have no idea how to approach the first part because we're not given the radius of the light.

It is small. Consider it a point source of light. It will illuminate the surface: the light rays cross the water surface and arrive to the eyes of the observer. But not all rays can escape from the water: Find the angle where the rays incident on the surface of the water totally reflect. Make a drawing!

ehild

 

[JSGandora]

Ohh, thank you so much. It's just the critical angle, or 48.6 degrees, making the radius to be 1/tan(48.6)=1.13m.

 

[ehild]

It is correct.

ehild