**3.3 Total internal reflection in fibers**

Light rays traveling from a denser medium to a rarer medium speed up at the boundary. This causes the rays to bend when they pass from glass to air at an angle

**Figure 5.** *Light travels in an optical fiber cable (credit: ProMotion/fotolia).*

**Figure 6.**

*Total internal reflection in an optical fiber.*

**Figure 7.** *Light rays undergo total internal reflection inside an optic fiber that is bent.*

other than 90°. This is called refraction. The two layers of plastic form the two mediums on which the reflections occur (**Figure 6**).

Beyond a certain angle, called the critical angle, all the waves reflect back into the glass. We say that they are totally internally reflected. The light rays stay inside the optic fiber and are transmitted over long distances with negligible loss (**Figure 7**).
