| Total Internal Reflection :- When the light source is in the denser medium as the angle of incidence increases so does the refracted angle in the less dense medium into which it escapes. Eventually, the refracted angle reaches 90º and the light is totally internally reflected BACK into the more optically dense medium. The unique angle when this phenomena first occurs is called the critical angle, ?c. In the diagram shown below, you can see that rays #1, #2, and #3 are refracted from the prism along its hypotenuse; while rays #4 and #5, after being totally internally reflected off the hypotenuse, are only refracted out of base of the prism. Also notice the relative intensity of the five rays emerging from the base: #4 and #5 are equally bright while #1, #2, and #3 show less intensity since they were only partially internal reflected off the hypotenuse.
The following formula allows you to calculate the critical angle at which all the light is totally internally reflected and none is refracted n1 sin(?1) = n2 sin(?2)
n1 sin(?c) = n2 sin(90º)
n1 sin(?c) = n2 sin(?c) = n2/n1 Notice that this is merely a rearrangement of Snell's Law in which ?2 = 90º. Remember that total internal reflection can ONLY occur when the light BEGINS in the denser medium - for example, the light starts in water and is bounced back into the water at the water-air interface. Notice that ?reflected = ?critical according to the Law of Reflection. | 
Back to Community Shelf
Awaiting Review for Nickels![[Post New]](/templates/default/images/icon_minipost_new.gif){kind=icon}
222
