Calculating Difference in Speed of Light in Glass: Help Needed!

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Homework Help Overview

The discussion revolves around calculating the difference in the speed of light in glass for different colors, specifically blue and red light, based on their refractive indices. The original poster presents a problem involving the time interval for light traveling through an optical fiber made of glass.

Discussion Character

  • Exploratory, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to calculate the difference in speed of light for blue and red light using the refractive index. They express uncertainty regarding the subsequent part of the problem, which involves determining the time interval for light traveling through an optical fiber.

Discussion Status

Some participants have offered guidance by referencing fundamental physics formulas, indicating a potential direction for the original poster's inquiry. However, there is no explicit consensus on the approach to the second part of the problem, and multiple interpretations of the question are being explored.

Contextual Notes

The original poster mentions specific values for the refractive indices of blue and red light, as well as the length of the optical fiber, which may influence the calculations. There is also a separate question posed about a lamp underwater, indicating a broader context of light behavior in different mediums.

CathyLou
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Hiya.

I'm really stuck on the following question. I think that I have got part a alright, but I've no idea what to do for part b. Any help would be really appreciated.

The refractive index of glass is 1.643 for blue light, and 1.618 for red.

(a) Calculate the difference in the speed of light in the glass for the two colours.

Okay, for this one I got that if n = C/V, for blue light V = 1.83 x 10^8 and for red light V = 1.85 x 10 ^8. Therefore, the difference is 2 x 10^6 m.s^1.

(b) If a very short pulse of white light is sent in a one end of an optical fibre made of this glass of length 1 km, find the time interval between the arrival at the other end of the red and blue light.

Thank you.

Cathy
 
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Go back to what was probably the very first fourmula you used in physics: d=vt.
 
Chi Meson said:
Go back to what was probably the very first fourmula you used in physics: d=vt.

Oh, yeah! Thanks so much for your help! :smile:

Cathy
 
I also had no idea how to work out the next question and would really appreciate it if someone could please help me out.

A diver working in water has a lamp which is 3 m below the surface. Viewed from above, the lamp produces a circle of light on the surface of the water. What is the diameter of the circle?

Thanks again.

Cathy
 
Last edited:

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