All material objects (bodies) emit electromagnetic waves with a characteristic spectrum. Letx be a spectral variable i.e., x is one of (, f, ) (wavelength, frequency, or energy). Considera region of the electromagnetic spectrum between x and x + dx. Then we define the radiationdistribution function dudx as the fraction of a bodys total energy per unit volume du radiated inthe region dx:du =dudx|dx|.The form of the radiation distribution function depends on the spectral variable we choose(but the energy per unit volume does not). Plancks law gives dudx for a blackbody. In terms ofwavelength we haveu :=dud =8hc51ehckT 1.(a) (1.5 pt) Derive uf .(b) (1.5 pt) Derive u.Hint: Energy, frequency, and wavelength are related by = hf = hc/ so an increment of thewavelength d > 0 corresponds to a decrement of frequency df < 0. From the definition,ud = uf |df| = uf df.If you are not using this, youre missing something important!