Absorption prob - why my way isn't correct?

[assaftolko]

Homework Statement

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

Homework Equations

E=hv, c=λv

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

 

[DrClaude]

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

I found [...] E2 using v2

correct?

 

[assaftolko]

Why not? Thought so...

 

[DrClaude]

Why not? Thought so...

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

 

[assaftolko]

Im sorry i don't quite get how to understand my mistake...

 

[DrClaude]

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

 

[assaftolko]

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

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

 

[DrClaude]

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

 

[assaftolko]

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

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?

 

[DrClaude]

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.

 

[assaftolko]

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.

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!

 

[DrClaude]

You're welcome!