# CMB Peak Fregenucy (Planck's law vs. Wein's law)

by redrum419_7
Tags: fregenucy, peak, planck, wein
 Sci Advisor P: 2,193 In short, the difference is because you have to transform the differential element $d\lambda$ to $d \nu$ (or vice-versa) rather than just substituting in the corresponding expression from the dispersion relation.