# Homework Help: Ionization and photon

1. Feb 5, 2010

### ricky red

This is the exercise:
Suppose that an hydrogen atom in its ground state absorbs a photon whose wavelength is 15 nm. Will the atom be ionized? If so, what will be the kinetic energy of the electron when it
gets far away from its atom of origin?

i have no idea how to procede!!! Someone can help me? Thank you!

2. Feb 5, 2010

### thebigstar25

first , what is the ionization energy? it is the minimm energy needed to remove an electron from an atom, and in your case you have a hydrogen atom which has an ionization energy of 13.6ev .. hint: you are given the wavelengeth of the photon find the energy from there then compare it with 13.6ev , if it is less then the atom wont be ionized .. if it is more then it will be ionized .. from there if it will be ionized, can you find out what will be the kinetic energy? ..

3. Feb 8, 2010

### ricky red

thanks for the hint. Well E=h*c/w =1.32E-17 J => 82.7 eV
So... Yes it will be ionized, and the kinetic energy should be 82.7-13.6 = 69.1 eV.
Is this right???

PS=don't know if this forum have an uniform use of the constant, in my calcolous:
h=planck costant, c=Speed of light and w = wavelenght

4. Feb 8, 2010

### thebigstar25

:) that seems logical enough and I believe that you got the right answer .. and welcome to the physics forum ..

but one thing I would like to add here, the problem you have would change, if for example the hydrogen atom wasnt in the ground state , if it was in the first excited state (second state) then you will need an energy of 3.4ev to ionize it ( since in this state it will have an energy = -3.4 ev, E2 = -13.6/4 ev )