Answer
a. $36.9^{\circ}$.
b. Horizontal.
Work Step by Step
The sunlight strikes the water surface at Brewster’s angle (the polarizing angle) because we know the reflected light is completely polarized.
Equation 33.8 tells us $tan \theta_p=\frac{n_b}{n_a}$.
$$tan \theta_p=\frac{1.333}{1.00}$$
$$\theta_p=53.1^{\circ}$$
The angle is measured relative to the normal to the surface, i.e., in this case, it is measured off the vertical.
The sunlight is incident at an angle of $90^{\circ}-53.1^{\circ}=36.9^{\circ}$ above the horizontal.
b. Figure 33.27 shows that the plane of the electric field vector, after light reflects from the lake, is horizontal.
