I am having some trouble w/ a take home Physics final. I am down to my last 2 questions: 1) What is the frequency for a photon emitted from a hydrogen atom when an electron makes a transition from an energy state n=3 to n=1? What is the energy of the photon in Joules and MeV? 2) A positron and an electron collide and annihilate each other. Since all of each of masses was converted into energy, how much energy was released in Joules? All the help/direction you can give would be much appreciated.