How Does Light Refraction Affect the Diameter of a Light Cone in a Pool?

[21385]

Homework Statement

At the shallow end of a swimming pool, the water is 70.0 cm deep. The diameter of the cone of the light emerging from the water into the air above, emitted by a light source 10.0 cm in diameter at the bottom of the pool and measured by an observer on the edge of the pool 2.50 m away, is
a) 1.60 m
b) 1.70 m
c) 1.75 m
d) 1.80 m

Homework Equations

nsin(angle)=nsin(angle)
nsin(criticalangle)=nsin90

The Attempt at a Solution

I am really confused, can anybody help me? I don't know where to start.

Thanks

 

[enricfemi]

i don't sure the situation is clear. how tall is the observer?

 

[Doc Al]

This is a critical angle problem. Draw a diagram of the light (at the bottom of the pool) being emitted at all angles. Figure out the maximum angle that will be refracted--anything greater will just be reflected by the water surface--and use that to calculate the diameter of the cone.