Chapter 18, Problem 44A

To determine

The angle of incidence in the glass.

Answer to Problem 44A

  $20.8°$

Explanation of Solution

Given:

The light travels from flint glass into ethanol.

The angle of refraction of the light, ${\theta }_2=25.0°$

Formula used:

Snell’s law of refraction,

  $n_1\sin {\theta }_1=n_2\sin {\theta }_2$

Where,

  $\begin{array}{l}{n}_1=\text{ index of refraction of first medium}\\ n_2=\text{ index of refraction of second medium}\\ {\theta }_1=\text{ angle of incidence}\\ {\theta }_2=\text{ angle of refraction}\end{array}$

Calculation:

It is known that,

Index of refraction of flint glass, $n{1}_{}=1.62$

Index of refraction of ethanol, $n{2}_{}=1.36$

Then, using Snell’s law of refraction, angle of refraction will be,

  $\begin{array}{c}{n}_1\sin {\theta }_1=n_2\sin {\theta }_2\\ \left(1.62\right)\sin {\theta }_1=\left(1.36\right)\sin 25.0°\\ {\theta }_1={\sin }^{-1}\left(0.355\right)\\ =20.8°\end{array}$

Conclusion:

Hence, the angle of incidence in flint glass is $20.8°$ .