How necessary is upper level E&M for QM

[koab1mjr]

Hi

I want to take a year long QM squence at my school but the prereqs is a year long sequence in E&M. I was wondering what skills are picked up from E&M that is used in QM. I have taken modern physics which had light exposure to QM and I did not see much drawn from what little E&M i know.

If I wanted to test out after some self study what's a nice E&M book to self study with

From a math standpoint i would declare myself intermediate as i am know dabbling in real and complex analysis stuff.

Thanks in advance

 

[SpectraCat]

Well, if you are going to get into quantum field theory in your Q.M. class (and I guess you will in a year-long sequence), then E&M will be very helpful, if not essential, since that is where one usually learns to deal with the details of vector calculus.

Jackson's "Classical Electrodynamics" is the quintessential E&M text, and gives a thorough treatment of the subject, but I am not sure I would characterize it as "nice to study with".

 

[koab1mjr]

there are some scary comments about this book. While the math does not scare me the holes in explanation do. And they seem to be referring this as a grad level textbook is that the case?

 

[SpectraCat]

there are some scary comments about this book. While the math does not scare me the holes in explanation do. And they seem to be referring this as a grad level textbook is that the case?

I have seen it used for both grad and undergrad classes (I used it as undergrad). I have also heard the same critical comments about "holes in explanations" ... in my personal experience with the text, the "holes" were filled by the professor during lecture. However, you might also want to consider a "companion" text, such as Fleisch's "A student's guide to Maxwell's equations", that explains things at a bit lower level.

 

[Phyisab****]

Where did you go that you used jackson as an undergrad? Was it a least an honors class or something? That seems like a great way to just completely destroy the sanity of a lot of well intentioned undergrads.

 

[Fredrik]

I was wondering what skills are picked up from E&M that is used in QM.

I would say "almost none". The class based on Jackson's book was probably the most useless class I ever took. Even when you study quantum electrodynamics, you're not going to be needing the stuff from Jackson. You can learn the parts you need directly from your QFT book. Also, you're talking about introductory classes to QM, not about QED. So Jackson is even less useful for you.

I think Jackson is much more useful for people who intend to work with the applications of physics than for people who just want to be prepared for graduate school. (A theory nerd is much better off taking another math class, say advanced analysis or differential geometry). In another one of these threads, one of the experimentalists here (I think it was ZapperZ, but I'm not sure) said that he actually uses the stuff from Jackson at work.

Where did you go that you used jackson as an undergrad? Was it a least an honors class or something?

I have to ask... I keep getting confused by how people use the terms "graduate" and "undergraduate" in this forum. How are those terms defined in the USA? I mean, how many years have you studied when you go from undergraduate to graduate? I was especially confused when someone said (in another thread) that Sakurai is a graduate book. It was what we used at the start of the third year. Jackson was at the start of the fourth year I think. There was no such thing as "honors" at our university.

Here in Sweden, you do 4 or 4.5 years before you get to apply to a graduate school. A graduate student is someone studying and working to get a Ph.D. This is a job you get paid for. It's supposed to be the equivalent of 1.5 years of studies and 2.5 years of research, but usually takes 5 years to finish. One of the reasons for that is that you're supposed to do some teaching as well.

 

[cmos]

Replying to the original post, I assume you are talking about an introductory QM course (i.e. a junior/senior level undergard course), right? In that case I doubt you'll see a lot, if any, QFT. With that said, I would say that unless your school has a very specific curriculum, then you would be fine taking QM before EM.

The only place where some knowledge of EM comes in handy in an introductory QM course is time-dependent perturbation theory. Applications of this include calculating transition rates between energy states. Even then, if you could take for granted electric and magnetic dipoles, then there isn't much else you absolutely need.

As others have said, Jackson is a graduate level text for EM. The undergrad standard is Griffiths (Intro. to Electrodynamics). Funny thing is that one of the standards for undergrad QM is also Griffiths (Intro. to Quantum Mechanics).

As a related aside, I've heard of some universities changing their curricula to teach QM (junior year) before EM (senior year). The rational being that the students would then be more apt for senior year research with earlier exposure to QM.

 

[Phyisab****]

Frederick: In the US undergrad is a 4 year degree, but there is about a years worth of non-technical courses required in the first two years, which I've heard is not the case elsewhere.

 

[CastorPollux]

Just to reiterate, because a lot of people have been throwing the word Jackson around. Typically Jackson is not used until the graduate level, so you don't have to scale that mountain just yet. Although, if you do theory, you may have the great fortune of using Landau and Lifschitz instead of Jackson. Enter the crazy Russians.

Take QM before EM, as long as you've seen some multivariable calc, linear algebra, and know what imaginary numbers are, you'll be fine.

Someone else talked about David J. Griffiths. I would like to profess that I have never been quite as taken with any book as I was with his Intro. to Electrodynamics. No one can do quite what he can in one little book - present the beauty of math with clarity of exposition, physical reasoning with intricate proof, additional problems designed to take you to the limits of your understanding and then push the boundary a bit farther. There's an intermission, as he says that all the underlying framework is in place, and you will then begin looking at the applications. He even manages to keep it light and crack some jokes. I refrained from sending him fan mail at the end of the course.

His QM book isn't quite up to the standard he set with Electrodynamics, but then again, nothing can be.

 

[Matterwave]

All I know is, whatever you do, don't use Wangsness's Electromagnetic Fields textbook...holy crap that book was boring...and dense!

 

[CKtalon]

The concept of using orthogonality in solving the Laplace equation through Fourier Series, etc might be useful when you study QM. Orthogonality is used much more in QM than EM though.

 

[ZapperZ]

I would say "almost none". The class based on Jackson's book was probably the most useless class I ever took. Even when you study quantum electrodynamics, you're not going to be needing the stuff from Jackson. You can learn the parts you need directly from your QFT book. Also, you're talking about introductory classes to QM, not about QED. So Jackson is even less useful for you.

I think Jackson is much more useful for people who intend to work with the applications of physics than for people who just want to be prepared for graduate school. (A theory nerd is much better off taking another math class, say advanced analysis or differential geometry). In another one of these threads, one of the experimentalists here (I think it was ZapperZ, but I'm not sure) said that he actually uses the stuff from Jackson at work.

I do. In accelerator physics, one such area is designing accelerator structure and cavity that's filled with RF field. So this is EM field with some exotic boundary conditions. We also deal with beam dynamics in various EM field geometry and modes.

So certainly, in accelerator physics, Jackson's text (or equivalent) is flat-out a requirement. I don't know about QED though.

Zz.

 

[Phyisab****]

True orthogonality of functions is an important concept. I took EM as a sophomore and had never even heard of orthogonal functions. When I tried to get help my professor could not even comprehend my level of ignorance. That chapter on Laplace's equation was so brutal. Some schools require a class on PDE's before EM or quantum, which is pretty helpful in my opinion.

I'd say the bigger obstacle is not that any particular knowledge from EM is required in quantum, but if you have not taken any upper division physics and you jump right into a course which is typically for seniors at your school, you may lack the "mathematical maturity" so to speak.