# Bohr Atom ?

Discussion in 'Physics' started by Bigcountry, Jun 5, 2010.

1. ### Bigcountry Thread Starter Active Member

Jul 4, 2008
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I am having problems figuring this out. It is about the excitation energy.

I hope some one could help me.

The excitation energy is defined as the difference in energy of the electron in the excited state and in the groundstate. A hydrogen atom is in an excited state in which excitation energy is 12.75 eV. A photon with energy

then they put in a hint: Before going to excited state of the -3.40 eV, the atom was in the ground. Thus, the excitation energy for the this first transition much be calculated. The excitation energy for the second transition to 12.75eV is the difference between this energy and 12.75eV. If the 12.75eV is greater than the energy of the first transition then energy muust have been absorbed by the atom.

I am having trouble finding what i need to calculate.

2. ### lendo1 Active Member

Apr 24, 2010
34
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If you could please rewrite the question exactly as stated, it would be much easier to understand. It looks like the answer is 12.75 eV - 3.40eV or 12.75 - (-3.4) --- which would be illogical, right? ---, but it is hard to tell because of the way you designed your question!

3. ### Bigcountry Thread Starter Active Member

Jul 4, 2008
71
0
I think it would be easier if i put the answers. At least I am not the only one confused.

A photon with energy

1) 2.55eV was absorbed
2) 2.55eV was emitted
3) 12.75eV was absorbed
4) 12.75eV was emitted

I think the hint threw me off and the wording of the question seems unusual.

thanks for helping me.

4. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
The issue raised is that your statement of the question has several typos that obscure what is being asked. Knowing the potential answers helps, but it is still necessary to know unambiguously what the question is.

John

5. ### Bigcountry Thread Starter Active Member

Jul 4, 2008
71
0
To eliminate the problem with the question I decide to just scan the question straight out of the book. I hope this works.

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6. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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As a first step, have you calculated the ground state energy? You can look it up easily enough (-13.6 eV), but if you don't know how to calculate it, you will be cheating yourself. That value will then allow you to calculate the energy of the first transition. Thereafter, follow the instructions in the hint to get the correct answer.

John

Last edited: Jun 7, 2010
7. ### Bigcountry Thread Starter Active Member

Jul 4, 2008
71
0
what is the ground state equation to use. i think it is

-Z( En/N^2)

since it is at the ground state N would be 1 correct?

8. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
In the Bohr atom, n=1 for the ground state.

John

9. ### Redbelly98 New Member

Jan 16, 2010
5
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Though this has probably been solved by the OP by now, it's worth pointing out the different energy reference levels being used. Presumably this confusion is a deliberate attempt by the question's author to make students think about the two commonly used reference levels.

"Excitation energy" is in reference to the ground state (n=1), whereas just referring to "the energy of -3.40 eV" is in reference to an ionized hydrogen atom (n→∞).