Total internal reflection

 

View the video above. You will see that the light coming from the laser is trapped in the column of water. Only to be released at the very end. The light bounces inside the column of water and only escapes when it gets to the very end. Optical fibers work in exactly the same manner.

Low grade optical fibers are used for signs and advertsing. Have a look at the video on the right. This was done with low grade optical fibers.

 

 

When light enters an optical fiber at a certain angle, known as the critical angle, it is reflected internally and trapped inside the fiber , as shown on the right. This is the bases of modern telecommunication involving optical fibers and some very impressive light shows at Crown Casino in Melbourne.

Click to read more about total internal reflection, then explain the disappearing coin trick as seen on the right and answer the questions below.

What is the critical angle?

Using the term "total internal reflection" explain why the coin appears to vanish.

 
Looking a the video on top why can we not see the light trapped in the water fountain at point "B"?