Question

At what angle is light inside crown glass completely polarized when reflected from water, as in a fish tank?

Short answer

The angle is ${41.2}^{\circ }$.

Step-by-step solution

 Step 1: Definition of polarisation

The term polarised refers to a medium that shows polarisation.

Finding the angle

The equation is used to solve this problem $\tan \left({\theta }_b\right)={\displaystyle \frac{n_2}{n_1}}$ where $n_1$ is the index of reflection for air and for water, is the index of redfraction for water is $n_2$.

$\begin{array}{rl}\tan \left({\theta }_b\right)& ={\displaystyle \frac{n_2}{n_1}}\\ & ={\displaystyle \frac{1.33}{1.52}}\\ & =0.875\end{array}$

Solving for the angle, we get

$\begin{array}{rl}{\theta }_b& ={\tan }^{-1}(1.14)\\ & ={41.2}^{\circ }\end{array}$

Therefore, the angle is ${41.2}^{\circ }$