Chapter 18.1, Problem 10SSC

To determine

Whether there is a critical angle for light travelling from glass to water, or from water to glass.

Answer to Problem 10SSC

Critical angle will be there when light travels from glass to water.

Explanation of Solution

Introduction:

When a ray of light moves from a medium of higher index of refraction in to a medium with a lower index of refraction, then light reflects back to its incident medium for certain angles. This phenomenon is known as total internal reflection. And, the angle of incidence at which the ray of line lines along the boundary of the mediums is called critical angle which is given as,

  $\sin {\theta }_c=\frac{n_2}{n_1}$

Here, $n_1$ is the index of refraction of incident medium and $n_2$ is the index of refraction of refracting medium.

Now, it is known that index of refraction of glass is greater than the index of refraction of water, that is,

  $n_{water}<n_{glass}$

Hence, when the light ray travels from the glass to water, then only total internal reflection occurs and then only there will be critical angle.

Conclusion:

Hence, there will be a critical angle when light travels from glass to water.