# Homework Help: Velocity in fiber optics cable

1. Aug 23, 2011

### mmanu

1. The problem statement, all variables and given/known data
I'm taking an introduction course in optics and I came across this exercise which I can't find how to solve:
"Two light pulses with different wave lengths 500 and 600 nm is sent in to a 1 km long fiber.
n(610 nm) = 1.399, n(600 nm) = 1.400, n(510 nm) = 1.448, n(500) = 1.45.
When will the two pulses come out of the fiber relative to each other?"
(Hopefully the translation is OK..)

2. Relevant equations
I suspect that I might need to use group velocity (http://en.wikipedia.org/wiki/Group_velocity), but this has not been taught in the class so far, so perhaps there is an easier way to tackle the problem??

3. The attempt at a solution
Nothing that has ended up embarrassingly wrong... :/

BR
/Manu

2. Aug 23, 2011

### Hootenanny

Staff Emeritus
Welcome to Physics Forums, mmanu.

So you have been given the refractive index of the fibre optic cable for a range of frequencies. How is the refractive index defined?