J-Space Calcs - Learn Quantum Mechanics

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Piano man
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Hi,

I'm currently studying my Quantum Mechanics notes from college last year and I've got to the bit about j-space calculations. The slide is very scant on details and google isn't yielding anything on this either.
I would skip it but it seems important for deriving expressions such as Energy E(\lambda)d\lambda =k_b T\left[\frac{8\pi L^3}{\lambda ^4}\right]d\lambda and the energy density in a cavity u(\omega)d\omega = \frac{\hbar\omega^3}{\pi^2c^3}\frac{1}{e^{\hbar\omega/k_bT}-1}d\omega

Does anyone have any good sources for learning more about j-space?

Thanks
 
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