Calculating Wavelengths in de Broglie's Standing Wave Condition

[powerof1004]

Homework Statement

de Broglies standing wave condition demands that an inegral number of wavelengths fit into the circumference of the Bohr orbit. How many "interal wavelengths" are there in the fourth exited state of Be3+?

Homework Equations

n lambda = 2 pi r

The Attempt at a Solution

i tried to solve using the equation above but was confused on lambda and r, both unknowns.

n = 5 because of fourth excited state i think
not sure what use the charge is in this problem...

 

[PeterO]

Homework Statement

de Broglies standing wave condition demands that an inegral number of wavelengths fit into the circumference of the Bohr orbit. How many "interal wavelengths" are there in the fourth exited state of Be3+?

Homework Equations

n lambda = 2 pi r

The Attempt at a Solution

i tried to solve using the equation above but was confused on lambda and r, both unknowns.

n = 5 because of fourth excited state i think
not sure what use the charge is in this problem...

It seems to me the question is asking for the number of wavelengths, not a value/size of each wavelength. You had answered that. Perhaps I misread, or there was more to the question than you wrote ??

 

[SpecialKM]

Yeah, I think you just answered your own question. As you said, there are 5 internal wave-lengths.

 

[powerof1004]

Yeah, I think you just answered your own question. As you said, there are 5 internal wave-lengths.

really??
but i just used one piece of info and totally disregarded the rest and didnt use any formulas...

 

[PeterO]

really??
but i just used one piece of info and totally disregarded the rest and didnt use any formulas...

As I said, the [part of the] question you posted did not include any information which you feel you have "totally disregarded" ?

EDIT: And don't get hung up on always wanting to use a formula.

 

[powerof1004]

I didnt use Be3+ or any of the information of the circumference. I just came to n=5 due to fourth excited state.
wouldn't that be disregarding the other pieces of information?

 

[PeterO]

I didnt use Be3+ or any of the information of the circumference. I just came to n=5 due to fourth excited state.
wouldn't that be disregarding the other pieces of information?

If the question had said:

"How many "interal wavelengths" are there in the fourth exited state"

people may be wondering "How many "fourth exited state of what?"

I think the use of Be3+ is just there because some atom had to be.

 

[powerof1004]

Wow than this was a much simpler problem than i thought it would be
Thanks Guys