Kinetic Enegry and Hydrogen Atoms

[ljucf]

Homework Statement

(a) What is the minimum kinetic energy in electron volts that an electron must have to be able to ionize a hydrogen atom (that is, remove the electron from being bound to the proton)? Answer: 13.6 eV

(b) If electrons of energy 12.8 eV are incident on a gas of hydrogen atoms in their ground state, what are the energies of the photons that are emitted by the excited gas?
Energy of highest-energy photon: 12.8 eV
Energy of next highest-energy photon: 12.089 eV
Energy of next highest-energy photon: 10.2 eV
Energy of next highest-energy photon: 2.6 eV
Energy of next highest-energy photon: 1.9 eV
Energy of lowest-energy photon: ?? eV

(c) If instead of electrons, photons of all energies between 0 and 12.8 eV are incident on a gas of hydrogen atoms in their ground state, what are the energies at which the photons are absorbed?
Energy of highest-energy dark line: 12.8 eV
Energy of next highest-energy dark line: 12.089 eV
Energy of lowest-energy dark line: 10.2 eV

Homework Equations

-13.6/n²

The Attempt at a Solution

I thought you would take 12.8-12.089 = .711 eV, however it states this is wrong. I have tried answers 0, .7, .711, and .6. Not sure why it's wrong.

 

[Simon Bridge]

OK - so how was the highest energy photon generated?

 

[ljucf]

OK - so how was the highest energy photon generated?

Due to the fact that the questions says 12.8eV is the ground state, wouldn't that result in 12.8 being the highest energy photon?

 

[Simon Bridge]

Due to the fact that the questions says 12.8eV is the ground state, wouldn't that result in 12.8 being the highest energy photon?

The question does not say that 12.8eV is the ground state.
What is the ground state energy of a hydrogen atom?

But you didn;t answer the question: what is the mechanism that generates the photons?

BTW: are those numbers given to you are did you work them out?

 

[ljucf]

E_n=K+U_e=-13.6eV/N²

-13.6/N_o²+13.6=12.8

N_o²= -13.6/0.8= -17
√(17) ≈ 4

-13.6/4²+13.6=12.75

 

[ljucf]

BTW: are those numbers given to you are did you work them out?

I worked them out.

 

[Simon Bridge]

That's just a bunch of equations - please use English to explain what you are doing.
What is the physical process you are thinking of ... an electron flies through the gas, it encounters a H atom, and then what does it do?

 

[ljucf]

That's just a bunch of equations - please use English to explain what you are doing.
What is the physical process you are thinking of ... an electron flies through the gas, it encounters a H atom, and then what does it do?

I have know idea...I am using the equations that were given in class.

 

[ljucf]

I solved it.

-13.6/4²+13.6/3²=.66

 

[Simon Bridge]

Well great - but I have no idea what you did because you have not used an physics.
It sounds like you don't know either. This does not bode well for the future - when there will be no equations given in class.