# Homework Help: Quantum physics- kinetic energy of electron after collision

1. Oct 2, 2014

### desmond iking

1. The problem statement, all variables and given/known data

since the bombarding electron has only 7.0eV ... it's not sufficient for the electron in the ground state to be excited which needs 10.4eV , so no excitation occur. and in my opinion, the bombarding electron should emerge with the same amount of energy .... but the ans given is here different . Can somoene explain what's the ans is about? thanks!

2. Relevant equations

3. The attempt at a solution
SAMPLE ANS : 7.0- ( (-3.7eV) - (-10.4eV) ) = 0.3eV...

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2. Oct 2, 2014

### nasu

The picture does not show what the question is.
You cannot discuss the answer unless you know the question.:)

3. Oct 3, 2014

### desmond iking

Sorry.. The question should be
If the kinetic energy of an electron 7.0eV collides elastically with an atom in ground state , what's the kinetic energy of the elctron after collision? Ps I forgot to post the question........

4. Oct 3, 2014

### nasu

It need 10.4 eV to ionize the atom but not to excite it.
The atom can go from the ground state to one of the other states in the diagram. This transition will require less than 10.4 eV. Which transitions are possible in this case?

5. Oct 3, 2014

### desmond iking

-10.4eV to- 5.5eV , -10.4eV to -3.7eV are possible

6. Oct 3, 2014

### nasu

What will be the KE of the initial electron after each of these two processes?

7. Oct 3, 2014

### desmond iking

for -10.4eV to- 5.5eV , using ke= hf-W
i have ke= 7.0eV - ( 10.4-5.5) = 2.1eV
for -10.4eV to -3.7eV , i have ke= 7.0eV - ( 10.4-3.7) =0.3eV

so? what does it mean?

8. Oct 3, 2014

### nasu

What do you mean?
What was the question, again?

9. Oct 3, 2014

### desmond iking

If the kinetic energy of an electron 7.0eV collides elastically with an atom in ground state , what's the kinetic energy of the elctron after collision?

10. Oct 4, 2014

### nasu

So what did you find in the previous calculation? Were not these values of kinetic energy after collision?