How Do You Calculate Group and Phase Velocities for a 550nm Wavelength?

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To calculate group and phase velocities for a wavelength of 550nm, the user needs to determine the refractive index (n) from a provided tab. The relevant equations are v(phase) = c/n and v(group) = dw/dk, with the relationship v(phase) * v(group) = c²/n². Interpolation is suggested as a method to find n, but it is emphasized that the equations may not hold true universally, as they imply v(phase) equals v(group) in all cases. Understanding the context and validity of these formulas is crucial for accurate calculations.
Dassinia
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Hello

Homework Statement


I have this tab
http://img18.imageshack.us/img18/3317/eyph.png

Anf I have to find the group and phase velocities for a wavelength λ=550nm

Homework Equations


v(phase)= c/n

v(group)=dw/dk

v(phase)*v(group)=c²/n²


The Attempt at a Solution


I don't know how I can determine n for the wavelength of 550nm using the tab ?
I was absent the day of this course
Can I use the relation v(phase)*v(group)=c²/n² ?

Thanks !
 
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Dassinia said:
v(phase)= c/n
v(phase)*v(group)=c²/n²
Where do those two formulas come from? Where are they valid? Can you use them here?

I don't know how I can determine n for the wavelength of 550nm using the tab ?
Do an interpolation.
I was absent the day of this course
Interpolation is a much more general concept you should know.
 
The formulas come from my book, for electromagnetic waves.
Why can't I use them ?
OK, so I'll do an interpolation !
Thanks
 
Those equations would give v(phase)=v(group) everywhere, which is not true.
Please check how they got defined, and where they are applicable.
 

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