Please help with Physics... hydrogen atom absorbs photon of energy, how does the kinetic energy change????

Question

When the hydrogen atom absorbs a photon of energy Ephoton resulting in the atom being in an excited state, the kinetic energy of the electron changes by

a)-Ephoton

b)-Ephoton/2

c)Ephoton

d)2Ephoton

e)0

also....

When the hydrogen atom absorbs a photon of energy Ephoton resulting in the atom being in an excited state, the potential energy of the electron changes by

a)-2Ephoton

b)-Ephoton/2

c)0

d)-Ephoton

e)2Ephoton

I know the correct answers are a) and e), but I don't understand how one reaches that answer. Thanks for any help you can give.

Answer 1

Im guessing but, id go with:

1) e

2)d  

Im assuming you meant to put positive instead of negative

For the first question I chose "e" the electron absorbing energy will not cause it to physically move to the next energy state  (So velocity will remain unchanged.  The angular velocity will probably be different, but thats another problem) .  What will happen is more like the electron will disappear and then reappear in its new energy state.....quantum mechanics is strage indeed.

On the other hand it is true that the electron will gain potential energy.

Thats why i chose "d" for question 2.  

You already know that it will be positive because the energy will increase.  But, I chose E instead of 2E because the source of the energy is only one photon.   if there were 2 photons, or another source of energy then id say 2E.

BEKKI:

Bekki  has a good point below, but...i'll stick to my guns.  Ignore that she is the best of us physics answerers ok (kidding).   It looks like she is referencing to tangential velocity due to its distance from the center...which i did say may decrease (angular velocity).  But, i think your question is not asking that.

Answer 2

According to the virial theorem (which, you can prove, holds in quantum mechanics), if the potential energy goes like 1/r, the average kinetic energy is related to the average potential energy by:

<T> = -1/2 <V>

The total energy is <T> + <V> = 1/2 <V> = -<T>

So if the total energy goes up by E, then <T> drops by E and <V> goes up by 2E.

Answer 3

1. The atom absorbed the photon, so its total energy has to go up.

2. An excited atom has the electron further out from the nucleus, so its potential energy is larger.

3. Electrons further out move slower than those further in, so the kinetic energy goes down.