Answer
The diameter of the circle is $~~4.56~m$
Work Step by Step
We can use Equation (33-45) to find the critical angle $\theta_c$ at the interface between water and air:
$\theta_c = sin^{-1}~\frac{n_2}{n_1}$
$\theta_c = sin^{-1}~\frac{1.00}{1.33}$
$\theta_c = 48.75^{\circ}$
The maximum refraction angle of the light as it enters the water is $48.75^{\circ}$
We can find the radius of the circle:
$\frac{r}{2.00~m} = tan~48.75^{\circ}$
$r = (2.00~m)~tan~48.75^{\circ}$
$r = 2.28~m$
Since the diameter is twice the radius, the diameter of the circle is $~~4.56~m$
