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In one of my textbooks, I'm given these two equivalent equations for energy flux radiated from a black body, one dependent on frequency, the other on wavelength:

[tex] I(\lambda)d\lambda = \frac {2c^2h}{\lambda^5} \frac {1}{e^{(hc/KT\lambda)}-1}d\lambda[/tex]

and

[tex] I(\nu)d\nu = \frac {2h\nu^3}{c^2} \frac {1}{e^{(hv/KT)}-1}d\nu[/tex]

Now, I'm just trying figure out how are these equations equivalent? At first, I thought it was simple substitution of the relation [tex]\lambda = \frac{c}{\nu}[/tex], but that doesn't work... so I realize that you have to convert units by differentiating say in this case lambda, and I get the same equations with the exception of a negative sign which I can't see how it cancels.

To be quite honest, I'm just not sure I'm doing the converting right. I'm not exactly sure how to handle the left side of the equation in this case.

Any suggestions or references would be great... Thanks!

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# Homework Help: Black Body Equations (more of a math prob)

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