Q:  What is the total energy emitted in one second by one square meter of a
            blackbody at temperature T = 5800 K?


            E(tot)  =  sigma * T^4   =   5.67 x 10^(-8) * (5800)^4

                    =  6.4 x 10^7   Joules per second


  Q:  If all that energy has the form of photons with wavelength 550 nm,
            each with energy 3.61 x 10^(-19) Joules, how many photons
            must be emitted per second?


                              6.4 x 10^7  Joules per second
             N(photon)  =   -------------------------------------
                              3.61 x 10^(-19) Joules per photons


                        =     1.78 x 10^(26)   photons per second