Determine dispersion from fitting equation

AI Thread Summary
To determine the dispersion at a wavelength of 800 nm, the fitting equation y = 7e-15 x + 1.60 is used, where x represents 1/lambda^2. The user attempted to calculate the derivative of x, resulting in -2/lambda^3, but received an incorrect answer. The issue identified was the omission of the coefficient of x in the derivative calculation. Correctly incorporating this coefficient is essential for obtaining the right dispersion value. Proper application of the fitting equation and its derivative is crucial for accurate results.
mufc4ever
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1. Homework Statement

Determine the dispersion (dn/d lambda) at a wavelength of 800 nm from fitting equation.


2. Homework Equations

Fitting equation from graph of n vs 1/lambda^2

y = 7e-15 x + 1.60


3. The Attempt at a Solution

Since it is a plot of n vs 1/lambda^2 I thought that x would be 1/lambda^2 so I took the derivative of that to get -2/lambda^3 and then put in the number. However I did not get a correct answer consistent with earlier findings.

What am I doing wrong?
 
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You forgot the coefficient of x.
 

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