
$$
{\rm Energy\ of\ photon\ } \thinspace E = \thinspace h \thinspace \nu  =  \thinspace h \thinspace { {c}\over{\lambda}} 
$$


$$
 E =  \thinspace { {1240 {\rm \ eV\ nm} }\over{\lambda}}  \qquad \Longrightarrow  \qquad 
  { {\lambda } = \thinspace { { 1240 {\rm \ eV\ nm} }\over { E }} }
$$


$$
  E_n = {- { {13.6} \over {n^2} }} \thinspace {\rm \ electron Volts }
$$


\bye
