This video shows how to use boundary conditions along with the time-independent Schrodinger equation
to obtain the wave-function parameters for the bound states of a finite square well. Normalizing and actually matching the wave-functions at the boundaries, takes more work.
At 2:00 I say " the states will divide up into even and odd states",
but really I should have said "the energy eigenstates will divide up into even and odd states".
Added notes, 4-17: So basically the procedure you can use is:
1) obtain k as outlined in the video
2) use k to obtain b
3) use k to obtain B/A
4) use the normalization condition to obtain specific numerical values of A and B. That condition is that the integral from -infinity to infinity must be 1, so that the sum of three integrals for the three different regions. That sum must add up to one.
Added note, 4-17, 3:45 PM
The way one gets k in the video is totally fine, but there are lots of ways. All starting from the same place. For example, you can use: k2+b2=2mU/ℏ2, from the Schrodinger equation, and ktan(k)=b from the boundary conditions at x = 1nm. Feed those to Wolfram alpha and it will give you values of k and b which "belong to" particular energy eigenstates. This way is kind of appealing since you have a nice circle as part of your graph, with a radius proportional to U, and the values of b and k come together in pairs.
(In general it is: ktan(kL/2)=b. For our particular case, L/2=1 nm.)
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ReplyDeleteAt 26:00 in the video you incorrectly put the value for mc2. It should be 0.511x106eV but you forgot the 106.
ReplyDeleteIt does come out to 26.25 when you include the 106
DeleteAlso at 9:20, should that be a positive b on the right hand side?
ReplyDeleteyour right. Yes. I agree
DeleteI thought b should be positive as well.
ReplyDeleteyes. (use reply next time)
Delete