plankes constant

[james-p]

is it possible to calculate plankes constant from only knowing the frequency of a emited phonton and the speed of transition. if so how

thanks

[Schrödinger's hat]

Yes

As this looks a bit like a homework question, I'll let you do a bit of reading and come back when you have trouble.

[james-p]

no it is not for homwork i have just heard from my friend that it was possible but my physics teacher told my class that it was impossible.

although could you show me the equations if they are the same as my freinds.

he showed me that he startes with the speed of transition = frequency of the emited photon x the wave lenght

[Schrödinger's hat]

(the yes was a link if you didn't notice, but I suppose I was a bit curt) Well I guess it depends a bit on what you mean by speed of transition. Also it's not the frequency of the photon, but the range of frequencies, or the linewidth.

If you have something like this:

 

 

The position depends on the frequency, but some of the lines are fuzzier than others. It's a bit hard to distinguish from bloom in a photo, but if you get the chance to look through a good spectrometer it's easier to see.

 

There's something called the time-energy uncertainty principle.

[math]

\Delta E\Delta t /geq \frac{\hbar}{2}

[/math]

(or sometimes h, depending on how many dimension you have)

It follows naturally from the momentum-position uncertainty principle the second you think about relativity, but I think you can also derive it from non-relativistic models fairly easily, and I think it comes up if you apply some thermodynamics to the Schroedinger equation as well.

 

Now I come to what do we mean by uncertainty in time?

This was the source of a lot of argument, and you should read the wiki page for more info.

Eventually the conclusion was reached that it is the uncertainty in the time the transition will happen, or how long the excited state lasts before decaying.

This is what I took you to mean when you said it was the speed of the transition, but reading again, it may not have been (I'm not sure speed of transition is quite the right thing to ask of a quantum interaction, I certainly can't think of any way to gradually apply an operator).

[james-p]

thank you for your answer.