posted by Bob .
At what angle to the surface must a submerged diver in a lake look toward the surface to see the setting sun just along the horizon?
Let A be the required angle to the VERTICAL.
Snell's law says that, in this case,
N sin A = 1*sin 90 = 1
sin A = 1/N = 0.75
A = 48.6 degrees
where N is the refractive index of water.
The angle they want is 90 - A
therefore Theta= 19.87
therefore Theta=19.87 degrees