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I NEED HELP WITH QUANTUM MECHANICS

Anonymous Wed 14 Nov 15:35:45 2018 No.10140064 View Reply Original Report

Quoted By: >>10140077 >>10140221 >>10142255 >>10144159 >>10146650

>quantum mechanics midterm in two days
>prof is nice but explains like shit, literally writing entire blackboards at top speed and erasing the blackboard before asking if he can erase it. He doesn't upload explained solutions to his exercise sheets
>Forced to try to understand the exercises he's solving focusing completely on what is he doing OR copying them, losing track of what am I even writing and why.

So basically I understand the photoelectric effect and some operators, but I don't know how to solve monodimensional, bidimensional and tridimensional "particle in a box" problems. Is there any webpage that has solved exercises that could help me? I literally need a resource that holds my hand during the solving process and I'm sure I will be able to understand it after I analyze and repeat those solved examples.

Anonymous

Anonymous Wed 14 Nov 2018 15:40:20 No.10140072 Report

Quoted By: >>10140089

Griffiths QM book is pretty hand holdy in that exact way in Chapter 2(?)

Anonymous

Anonymous Wed 14 Nov 2018 15:43:19 No.10140077 Report

Quoted By: >>10140089

>>10140064
Why don't you read the textbook?

Anonymous

Anonymous Wed 14 Nov 2018 15:48:02 No.10140089 Report

Quoted By:

>>10140077
Because we don't have textbook. We have shitty powerpoints that are ignored by the prof since he usually tends to explain everything at lightspeed using the blackboard until the projector turns off from inactivity

That would be an ok way of teaching, but we aren't in a physics degree so pure maths are something we aren't used to. That combined with his eagerness to "show us why this is like that althought is very complex mathemathically and won't be asked in the exam" clutters up the class so much our minds end exploding, not knowing what's useful and what isn't.

>>10140072
Checking it out right now. Yes, I think it comprises what we've studied so far. Thanks

Anonymous

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Anonymous Wed 14 Nov 2018 16:15:09 No.10140151 Report

Quoted By:

Ok, since I have around 36 hours left and I’m frantically desperate I would like guidance from you anons to a brainlet like me.
Taking a look at previous midterms of this subject I find that these are the most asked topics:
- Photoelectric problems
- Particle in a box, “m” mass, “L” longitude and “n=0,1,2,3,4…” state. Asking max probability points, nodes, mean value of kinetic energy, and probability of finding the particle between a/x and a/y
- Same, but considering 2 or 3 energy values degenerate, determining their quantic numbers of their states and degeneracy value
- Evaluate commutators
- Armonic oscillator, calculate energy of fundamental vibrational state, frequency of photon traversing from V=X state to V=Y state
- Particle with mass m and energy E with [this wave function], determine of which of these operators is eigenfunction

So assuming I perfectly know how to solve photoelectric problems and I’ve almost dominated operators, in which order, from easier to harder, should I study this to be as prepared as possible for the exam? I’m assuming that I won’t be able to get a grip of everything so I need to timely wise determine which topic is going to be easier to understand and nail in the exam.

Anonymous

Anonymous Wed 14 Nov 2018 16:51:12 No.10140221 Report

Quoted By:

>>10140064
https://4chan-science.wikia.com/wiki/Physics_Textbook_Recommendations#Problem_Books_in_QM

Anonymous

Anonymous Wed 14 Nov 2018 17:13:54 No.10140267 Report

Quoted By:

Farlow’s intro to partial differential equations for scientists and engineers has a really good breakdown of taking the laplacian in 3d. It’s totally different from what you’re looking at, but it’s a good reference to understand how we add dimensionality to PDEs

Anonymous

Anonymous Wed 14 Nov 2018 19:27:03 No.10140568 Report

Quoted By: >>10140597

Get yourself quantum mechanics for dummies.

Anonymous

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Anonymous Wed 14 Nov 2018 19:41:57 No.10140597 Report

Quoted By:

>>10140568
No, get the manga

Anonymous

Anonymous Thu 15 Nov 2018 09:28:10 No.10142244 Report

Quoted By:

OP here, 26 hours left. I'm finally understanding the formulas applied to particles in unidimensional, bidimensional and tridimensional boxes. Next I'll have to dominate how to evaluate commutators, wish me luck.

Will update in 6 hours.

Anonymous

Anonymous Thu 15 Nov 2018 09:36:07 No.10142255 Report

Quoted By: >>10142620

>>10140064
put your cell phone on silent and take photos of the board
>2018
>problems like this

Anonymous

Anonymous Thu 15 Nov 2018 15:40:33 No.10142620 Report

Quoted By: >>10142782

>>10142255
Why not just record the whole thing on video?

Anonymous

Anonymous Thu 15 Nov 2018 16:55:20 No.10142782 Report

Quoted By: >>10142788

>>10142620
That isn’t allowed here because the profs don’t allow it, unfortunately

Anonymous

Anonymous Thu 15 Nov 2018 16:58:12 No.10142788 Report

Quoted By: >>10142796

>>10142782
did I fucking stutter
>put your cell phone on silent

Anonymous

Anonymous Thu 15 Nov 2018 17:02:45 No.10142796 Report

Quoted By:

>>10142788
I always do this. Quantum mechanics is a subject that will make you waste an entire hour of class if you stop paying attention during 2 minutes. Hell, I even lose track of what is the prof even doing even paying full attention

Anonymous

Anonymous Thu 15 Nov 2018 17:53:59 No.10142900 Report

Quoted By: >>10144115 >>10145115

OP here, 17 hours until the exam. Everything made sense through exercise solving, it’s really fun now that I get it! It wasn’t that difficult! I’m currently finishing commutators and I would only need to check some armonic oscillator exercises and i will probably be more than ready to pass the exam. Needless to say I’m on stims to absorb as much content without burning out. But really, seeing step-by-step solved exercises and understanding every step is what is really bearing fruit.

I will study for 3-4 more hours and probably the stims comedown will make me want to sleep, so then I will check my formulas until I pass out in bed and wake up early to continue checking my solved exercises.

Now I understand why upperclassmen told me that the exams of this subject are very short, the exercises can be solved in less than two minutes if you know what to do.

Anonymous

Anonymous Fri 16 Nov 2018 03:20:42 No.10144115 Report

Quoted By: >>10145693

>>10142900
How do you study commutators? Any good resources?

Anonymous

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Anonymous Fri 16 Nov 2018 03:43:01 No.10144159 Report

Quoted By:

>>10140064
"Particle in a box' typically means we apply Born-von Karmen boundary conditions, or in other words we study quantum mechanics on the Pointrjagyn dual of the box instead.
Let $H$ be a Hamiltonian that acts on the Hilbert space of sections $\Gamma(L^d,F) \cong L^2(L^d,\mathbb{C})$ of a FLAT Hermitian line bundle $B \rightarrow L^d$ . Let us suppose the Weil integrality condition is satisfied and a proper holomorphic polarization $P$ on the tangent bundle $TL^d$ is given to simply our discussion.
For each Hilbert section $\psi: L^d \rightarrow \mathbb{C}$ covariantly constant on $P$ (i.e. a $P$ -wavefunction), Born-von Karmen periodic boundary conditions means that $\psi$ descends to the quotient space $L^d/\sim \cong \mathbb{T}^d$ , where $x \sim y$ iff $y_i = x_i + L$ for some $1 \leq i \leq d$ and $y_j = x_j$ for all $j \neq i$ . Now since $L^d$ is compact, the Fourier transform $\mathcal{F}$ is an isometric, fibre-preserving automorphism on the Hilbert sections of the Hermtian line bundle $B\rightarrow \mathbb{T}^d$ , hence $\mathcal{F}\psi$ is a Hilbert section on the Hermitian line bundle $B' \rightarrow \mathbb{Z}^d$ , where $\mathbb{Z}^d$ is the Pontrjagyn dual of $\mathbb{T}^d$ . If $\operatorname{Spec}H$ is bounded from below, then spectrum of its "Fourier pullback" $\mathcal{F}^*H$ is isomorphic to $\mathbb{N}^d$ . These give rise to the discrete/quantized energy levels.
Hope this is clear enough.

Anonymous

Anonymous Fri 16 Nov 2018 14:44:04 No.10145115 Report

Quoted By:

>>10142900
How did it go anon?

Anonymous

Anonymous Fri 16 Nov 2018 19:43:09 No.10145693 Report

Quoted By:

>>10144115
Canonical computation relations aren’t bad at all. A lot of it is playing around with the equations

Anonymous

Anonymous Sat 17 Nov 2018 02:06:58 No.10146650 Report

Quoted By:

>>10140064
Most textbooks will include standard exercises like that. Binney and Skinner is my favourite and there's also a pdf of it online that can be found easily.

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