What is the peak wavelength, in angstroms, emitted from a type F star with a temperature of 6900 K?

Wien's displacement law says the maximum wavelength is given by 

λ_max = b/T  where b = 2.897721*10^-3 m.K and T is the absolute temperature (in K).

 

So λ_max = 2.897721*10^-3/6900 m = 4.2*10^-7 m

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I am glad that you are back Alan.   :D

We have missed you and no one could answer these questions :(