If $\displaystyle \theta$ is the angle at which the light ray strikes the surface of the water, $\displaystyle \phi$ is the angle at which the light ray continues into the water, $\displaystyle m_a$ is the "refractive index" in air and $\displaystyle m_w$ is the refractive index in water then $\displaystyle \frac{sin(\theta)}{sin(\phi)}= \frac{m_a}{m_w}$. If you know the angle, $\displaystyle \theta$, at which the light strikes the surface of the water, as well as the indexes of refraction, then the angle at which the light continues into the water is given by $\displaystyle sin(\phi)= \frac{m_w}{m_a}sin(\theta)$.
That follows directly if you know what "Fermat's theorem" **is** but I don't know what else you want.
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Last edited by HallsofIvy; Apr 24th 2017 at 06:58 AM.
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