Homework Help: Absorption prob - why my way isn't correct?

1. Mar 14, 2013

assaftolko

1. The problem statement, all variables and given/known data
A hydrogen electron is at its ground level when it's radiated in wave length of 94.92 nm. As a result it arrises to level a. then emission occures with frequency of 2.34*10^14 Hz and the electron falls to level b. What's the energy difference between the 2 levels

2. Relevant equations
E=hv, c=λv

3. The attempt at a solution
I found E1 using λ1 that's given to me, E2 using v2 given to me and substracted E2 from E1. Why isn't this way correct and you have to use rydberg's formula? whay the 2 don't give the same result? I got 1.94*10^-18 J

2. Mar 14, 2013

Staff: Mentor

You don't have to use Rydberg's formula, but is
correct?

3. Mar 14, 2013

assaftolko

Why not? Thought so...

4. Mar 14, 2013

Staff: Mentor

Make a diagram with the energy levels and the transitions, you will see.

5. Mar 14, 2013

assaftolko

Im sorry i dont quite get how to understand my mistake...

6. Mar 14, 2013

Staff: Mentor

Ok, lets try another approach. Can you tell me what happens in the last step of the process?

7. Mar 14, 2013

assaftolko

Energy is emitted from the electron so it "drops" to a lower energy level, closer to the ground level than it was at first after it arrived to level a

8. Mar 14, 2013

Staff: Mentor

And to what does the energy of the emitted photon correspond?

9. Mar 14, 2013

assaftolko

to hv... so what you're saying is that this energy is not the energy of level b with respect to the ground level, but with respect to level a?

10. Mar 14, 2013

Staff: Mentor

Exactly! You get directly the the difference in energy between the levels from the emitted photon. The difference between the ground state and level a is actually irrelevant here.

11. Mar 14, 2013

assaftolko

that's weird because you still don't get the correct answer - which should be 1.55*10^-19 J

Oh **** yes it does... Oh man :/

Thanks!

12. Mar 14, 2013

Staff: Mentor

You're welcome!