# Requency for a photon emitted from a hydrogen atom

1. May 3, 2005

### pak213

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.

2. May 3, 2005

### quasar987

1) The energy of an electron in an atom depends on the energy state he's in. The energy of the fundamental level (n=1) is -13.6 eV. Find the energy of n=3 in your book. You are told the electron jumps from the energy of n=3 to the energy of n = 1. Now according to the principle of conservation of energy, that energy must have gone somewhere: in the photon. The frequency of a photon is related to its energy according to $E = h\nu$

2) They just want to know the energy associated with the masses of the electron and positron. Use E = mc².