Question

Optical fibers are generally composed of silica, with an index of refraction around 1.44 How fast does light travel in a silica fiber? 

Answer 1

$$v=\dfrac{c}{n}=\dfrac{3\cdot10^8\ \dfrac{m}{s}}{1.44}=2.08\cdot10^8\ \dfrac{m}{s}.$$