Q:  What is the frequency of optical light at a wavelength of 550 nm?

                             c           3 x 10^8 m/s
             freq nu  =  ----------  =  ----------------
                         wavelength      550 x 10^(-9) m


                      =   5.4 x 10^(14) Hz



   Q:  What is the wavelength of the right-most symbol in this SED?
           What portion of the electromagnetic spectrum does it mark?


                                  c          3 x 10^8 m/s
               wavelength  =  ----------  =  ---------------
                              frequency      3 x 10^(17) Hz


                           =    1 x 10^(-9) m  =  1 nm      X-ray