Brewster Angle and Fresnel Reflection

What you are seeing: a light ray incident on an interface between two media at angle $\theta_i$ . Snell s law $n_1 \sin\theta_i = n_2 \sin\theta_t$ gives the refraction angle; Fresnel coefficients give $R_s(\theta_i)$ and $R_p(\theta_i)$ . At Brewster angle $\theta_B = \arctan(n_2/n_1)$ the p-reflectance vanishes; at the critical angle $\theta_c = \arcsin(n_2/n_1)$ (when $n_1 > n_2$ ) TIR sets in

Figure 1. Light at oblique incidence onto an n1-to-n2 interface. Method: closed-form Snell + Fresnel; reflectance curves R_s, R_p as functions of theta_i.

theta_i (deg)50.0

medium 1 (top)water

medium 2 (bottom)air

animation speed0

WHAT TO TRY

Sweep the incidence angle to Brewster: the p-polarized reflectance R_p drops to exactly zero, so reflected light is fully s-polarized. That is the angle polarizing sunglasses exploit to kill glare.
Go from glass to air and past the critical angle: the refracted ray vanishes and the light totally internally reflects, the principle behind optical fibres.
Change the media (water, glass, diamond): Snell law bends the refracted ray more for higher index, and both Brewster and critical angles shift with the index ratio.