Confused by my modern physics class

In summary: Is there a good or bad quality to Modern courses depending on the instructor? And finally, how often should you revisit something in order to really understand it?In summary, my lecturer is currently addressing modern physics. We solved the Schrodinger equation for hydrogen, and then into all the quantized angular momentum, intrinsic momentum... now we are into quantum statistics... he is explaining that a modern physics course is a general survey of many different topics, and the scope isn't to go into great depth on anyone topic. He also warned us that it is impossible to fully understand any particular part of quantum mechanics unless you first understand some other part of it!
  • #1
tim_lou
682
1
My lecturer is currently addressing modern physics. "we" (more like "he") solved the schrodinger equation for hydrogen, and then into all the quantized angular momentum, intrinsic momentum... now we are into quantum statistics...

Seriously, I have absolutely no idea what my professor is talking about in class, and I doubt that if anyone else is following (at least none of my friends are). It seems like my professor just keeps throwing ideas at us without explaining why or where they come from. Example: electrons have intrinsic angular momentum, when "adding" wavefunction, femions is +, boson is - (i forgot, it may be the other way around...) four quantum numbers of hydrogen atoms n,l,m_l,m_s, j, m_j...

My professor does explain things (somewhat) but they do not really make sense to me. Am I supposed to be that confused? Is this the way one learns intro quantum/modern physics?
 
Last edited:
Physics news on Phys.org
  • #2
You will be a bit lost the first time these concepts are explained to you...you just need to make an effort on your own time to try and comprehend the stuff.

And typically, a "modern physics" course is a general survey of many different topics and the scope isn't to go into great depth on anyone topic.

Explanation of things like intrinsic spin is not trivial. The spin quantum number comes out of the solution of the relativistic Schrodinger equation, which I assume your professor hasn't touched.
 
Last edited:
  • #3
In my first "modern physics" course as a sophomore, our professor warned us that it was impossible to fully understand any particular part of quantum mechanics unless you first understood some other part of it! :bugeye:

leright is right, at the level you're at now, lots of times a modern physics course just has to give you results with only a sketchy derivation or justification. The full treatment requires a lot of math and is usually done in a senior-level or graduate-school course. I didn't see the complete solution of Schrödinger's equation for the hydrogen atom (including the radial part with associated Laguerre polynomials) until graduate school.

It's a lot different from classical mechanics and E&M where you can see most of the basic derivations even in the freshman general physics course.

You do have a textbook, right? It's often helpful to look in other textbooks for alternate ways of presenting the material, too.
 
  • #4
Yes, there is a textbook for my class. But the textbook is just as terrible... it doesn't have any "real" justifications for anything...for example, like jj coupling (or whatever, don't know the name), it just says that some angular momentum may interact and put a whole bunch of selection rules and quantized number which I have no idea why they are quantized... I guess I can't blame the text for not going into full depths of complicated math...
anyway, I've picked up some intro quantum physics books, relativity and such from the library... but its just that the class is covering so much in so little time. When I begin to get a firm understanding of some topic, the professor has already moved two chapters ahead... We are on Chapter 8 and I haven't even fully understood Chapter 6 yet... : (

Trying to understanding something from the text is really painful... For instance, the last Saturday I was trying to spend most of my day studying (Yes, I study on Saturday...), but I ended up trying to verify the equation for magnetic moment... which wasted me 3 hours (trying to go into generalization)...Ultimately, I didn't sucessfully verify the equation and my studying goes to waste.
 
Last edited:
  • #5
Here's some advice someone once gave me when I started college:

Try your best to learn what's going on... but if you get stuck trying to really understand things and you just have to move on [because of time constraints], press your "I believe" button and move on. In my experience, a deeper comprehensive understanding doesn't come during that first exposure. You have to revisit the subject several times, at various levels [e.g. as a tutor, as a more advanced student, as a teaching assistant, as an instructor, etc...].
 
  • #6
I got through my Modern Physics class by using this motto: "Just shut up and calculate."

I'm now taking an Intro Quantum Mechanics class, and I'm kind of starting to see the logic behind this stuff, but just barely.
 
  • #7
Y'all are making me glad Modern was not a requirement for my undergrad, and I didn't take it -- I opted to just go hard core to take more of the upper-level stuff. But -- I am tending to think the quality of Modern depends significantly on the instructor/book/curriculum, since it is inherently of a survey-nature. I hear really good things about Modern from some schools, and really bad things from other schools.

So my questions: Is Modern a requirement in most programs nowadays? If so, what is the reasoning? For those that HAD modern -- what are their impressions? I feel I did OKAY (even fine) without it... but maybe in retrospect having a survey class would be good for perspective... maybe I'm lacking some perspective on the nature of physics in the modern world.
 
  • #8
Yep, it's pretty much a requirement everywhere. And yep, you will do a lot of calculating without knowing WHY. Modern physics texts are teasers for the material you'll encounter in later semesters, and most of them let you know beforehand that some of the derivations are beyond the scope of the text. It's a shame, since first impressions are usually lasting ones, and I know my impressions of certain subjects were tainted. If you're a go-getter, find yourself more advanced, undergrad texts that cover the material you're going through in your modern class and appreciate the Why.
 
  • #9
I took a 2 semester modern course using Kenneth Krane's Modern Physics. As a physics major, I was frustrated by the lack of mathematics in the book and a serious lack of challenging end of chapter exercises. The first semester was also for chemistry, materials science, and EE majors so it was conceptual since everyone's backgrounds were so varied. I think that physics departments see these courses as an extension of basic freshman physics. You learn mechanics and EM at a shallow level as a freshman, and then take the upper division courses. I think the same concept applies to these modern physics courses.
 
  • #10
Bingo! That's exactly it... it's a survey course. Most students can't handle a full-blown upper-level QM or nuclear physics or atomic physics course without having seen some of the basic stuff beforehand, just like most freshmen can't jump right into Symon or Marion for mechanics. Also, most upper-level courses don't do much with the history or the experimental side of the subject, and most "intro modern physics" textbooks provide some of that background.

You have to keep in mind that just by being here, you're not like "most students." How many other students do you know at your school who hang out on Physicsforums or other similar sites? :smile:
 
  • #11
jtbell said:
You have to keep in mind that just by being here, you're not like "most students." How many other students do you know at your school who hang out on Physicsforums or other similar sites? :smile:

That's something I noticed that blows me away. Most of my school bench comarades (and I'm talking final undergrand year) don't like physics! It's probably the scholarly discipline that they dislike the less but they are not passionate about it and they won't talk about it for fun. It's just a chore to them..

I guess I should consider myself lucky. I get to have fun even when I'm doing my "chores". :smile:
 
Last edited:
  • #12
jtbell said:
You have to keep in mind that just by being here, you're not like "most students." How many other students do you know at your school who hang out on Physicsforums or other similar sites? :smile:

It is funny because it is true... I often check this forum when I go on the internet...

I bet most of my friends don't even know that this website exists.
 
  • #13
tim_lou said:
It is funny because it is true... I often check this forum when I go on the internet...

I bet most of my friends don't even know that this website exists.

Tell them about it and see if they'll visit it. :rolleyes:
 
  • #14
jtbell said:
How many other students do you know at your school who hang out on Physicsforums or other similar sites? :smile:

While it's surely been around for a while NOW, I don't think Physicsforums was around when I was a student... (yep -- SHOCKING! )

I found PF the week I defended my PhD (hence the name... which I'll change to something more modest soon). Since I had lots of free time after defending, I inquiried the undergrads in the research lab -- and a surprising number of them knew and used the forum... but they probably aren't "normal" undergrads, since they are in the lab doing research.

I guess I'm just surprised Modern is a REQUIREMENT, not an ELECTIVE. I never took a "math methods" for that matter... I just took a lot of MATH.
 
  • #15
Did your freshman general physics course include "modern physics" topics? Some schools have a three-semester general physics sequence in which the third semester is mostly modern physics. Or else they have a two-semester sequence and do some modern physics during the last two or three weeks. But I think in those cases they also have a separate modern physics course.

Next year our separate intro modern course will become part of a three-semester calculus based general physics sequence.
 
  • #16
I remember during our first Modern Physics Lecture our professor busted out the gradient and derived the EM wave equation from Maxwell's equations. I went home that morning and told my girlfriend that I hit the limit of my academic abilities and could no longer be a physics major.

As the lectures went on, things got a bit easier to follow.
 
  • #17
That is exactly what I am talking about! My professor went straight to Fourier series, delta function, and Fourier inverse when we were doing Schrödinger's equation...couple lecturers later, we went over harmonic oscillator and hydrogen atom... I mean they were fascinating stuffs but everyone was totally lost when my professor was deriving stuffs in such a short amount of time.

Anyway, as time went on, I eventually understood the harmonic oscillator and some of Fourier series...
 
  • #18
There is a story of a baseball player who struck out the first time at bat in the Majors. The catcher was supposed to have said, "Welcome to the Majors". The player eventually went on to have a fairly good career in baseball inspite of the slow start. Well, when it comes to modern physics, I say welcome to the majors. Keep swinging. Everyone finds it hard.
 
  • #19
Sometimes I get a little discouraged because I don't know Fourier Transforms, Guassian Integrals and Differential Equations, but I guess we really don't need to know how to solve those things at this time.

Overall the professor is not that tough on us. We don't have to remember derivations for this class.

What is annoying is that people in my class like to get the professor off track. We were supposed to have learned the Hydrogen atom already and are supposed to be on spin and atomic physics. There are 3 other chapters where we are supposed to at least touch on having to do with bonding and particles, but I doubt it's happening. :( I will read it myself.
 
  • #20
I've had quite an interesting experience with my modern physics class this semester. We started out the first couple weeks with special relativity, and a small intro to general. That was all fine. I understood it well, I aced the first test, and we continued.

Then, all of a sudden, the professor hit the gas. Class started to get hard. Really hard. And the professor has just been breezing through all of the topics. Now, as the semester draws to a close, I only have 4 classes left before the final!

Yeah, I'd say it's been a pretty tough class.
 
  • #21
May I ask what modern physics texts are being used by everyone here?

I used Tipler when I was in college.
Recently, I've taught out of Serway.
 
  • #22
my textbook:
Modern Physics
For Scientists and Engineers
Third Edition

by
Stephen T. Thornton
Andrew Rex
ISBN: 0-534-41781-7

it's not a very good book in my opinion (I like my classical mechanics book much better (although not by Goldstein)).
 
  • #23
Harris Benson
 
  • #24
tim_lou said:
my textbook:
Modern Physics
For Scientists and Engineers
Third Edition

by
Stephen T. Thornton
Andrew Rex
ISBN: 0-534-41781-7

it's not a very good book in my opinion (I like my classical mechanics book much better (although not by Goldstein)).
I am also using this book, and I agree that it is not a great book. Interestingly enough, my school's library has a copy of Tipler's Modern Physics that I like more.
 
  • #25
Modern Physics
3rd Edition
Serway,Moses,Moyer(sp)

I like the book. I think it explains things well and also delves into the history and experiments behind the theories, very nice. Its a relief after using Knight for Intro Physics-...can't say I'm a fan of Knight.
 
Last edited:
  • #26
Interesting Thread. I am taking Modern right now as well. I think there are two students (out of ~30) that seem to be understanding the material. The average on the last test was in the forties. We are using the Bernstein, Fishbane, and Gasiorowicz book, which I dislike very much. I have learned nothing from it, and I have spent many hours reading it. However, I am actually one of the two students who are doing well in the class. The key for me, was understanding that it IS a survey course of very complicated ideas. The professor will go crazy with mathematics deriving various ideas, and most of the students freak out thinking they have to remember all the derivations. You need to concentrate on the concepts. There will be some mathematics on the tests, but nothing too involved like you might see in lecture. I am constantly asking myself, "what is the general idea here?" and "What is that general idea based on?".

Also, I have taken Calc III and am concurrently taking diff eq and math methods, which have exposed me to much of the mathematics already. The prereq is only calc II, but I feel sorry for anyone coming into the class with only calc II. I know there is a lot of pressure for the schools to get the physics degree finished in four years, and so they make the math classes corequisites when they should really be prerequisites. Physics is HUGE in terms of a knowledge base. It seems a bit absurd that anyone can be expected to get 'up to date' in the field after just four years. Attempting to do so will inevitably lead to many courses that go WAY too fast for the students.
 
  • #27
At my university, the general track is General Physics 1 and 2 as freshmen, and then Modern Physics frist semester of sophomore year. Again, as others have said Calc 3 is only a co-requisite. I am a freshmen now in Gen Physics 1, but started in Calc 3, so I will be ahead fo the game. I almost can't imagine how some of the students in my class are managing being only in calc 1 for the first time. Alot of class time is spent on teaching the math to the students who haven't seen it before.
In my opiion even in my general 1 class, I have benefits form being in higher math. When we did Newton's Law of Gravity, and studied Gravitational Potential, our profesor very very briefly touched on the fact that F = - grad U for a conservative force, and it was well over the heads of most people in the class. My clac 3 class is currently studying Green and Stoke's theorems and have studied conservative fields already so I was able to really understand the material in my General Physics class.
It would severly limit those that could begin their physics as a freshmen, but I think schools should really consider making Calc a PRE-requisite fot their classes and no co-requisites
 
  • #28
My "quick" observations concerning Modern Physics Courses

The issue that seems to arise from any Moden Physics course, and I am getting this impression from both my own modern course as well as comments from others, is that the course is "dumbed down" and we are all told that it is done that way. When you tell some one, again this is just a subjective observation, that they are being told the "dumbed down" version of something they tend to ignore it to become overwhellmed by what the real topic is.

If anyone's modern physics course is like mine it has been one set of disasters after another:

Hinting towards more advanced (general and yet sometime easier methods) of calculation for relativity without actually showing it.
For 2-3 weeks.

4 weeks on compton effect and the wave nature of matter.

3-4 weeks on schrodinger equation, with very little mathematics focus.

----

It seems like a waste, to me personally, to have a "concepts" course taught without truly discussing the concepts and without going over the mathematics.

If I had my way I would have much rather perferred that the requirement for modern physics be calculus 4 (I am at a 10-week term university, so 3 terms in a year), and/or a course on PDE's.

Because at least for how I learn, I can't truly understand a general concept until I have the tools to play with the concepts. Give me the mathematics, and I can sit all day with a parabolic-second order partial diff. eq. and be perfectly content. Likewise I will understand many more of the intricies of the subject, if the mathematics is there.

----

Oh and as a side note, I really dislike both Serway and Beiser (I don't have any book for the course, as the text is optional, and as a result is not ordered by the school bookstore; however, the professor takes all of his questions directly out of these two books, and many of his notes...which often times are either difficult to follow or do a lot of "hand-waving" at equations).

I ended up buying Modern Physics, by Frank Blatt (there is only 1 edition and it is from 1992), and a book titled: 6 Core Theories of Modern Physics by Charles F. Stevens. The latter is rather useful for more than just the modern physics course as it covers the methods for quantum, statisitical, classical, E&M, quantum field theory, and special relativity. Though Blatt isn't bad either. He leans a bit more towards the math, which is to my liking; however, from time to time he makes a "hand-waive" and then proceeds with his derivation...which is frusturating.


Oh well only 1 more term of it to go, and the next term we actually do some 3D schrodinger and a bit more of a survey of particle physics (though it is only about 3 weeks of that).
 
  • #29
One complication in a university program is that students come in with a variety of experiences and exposures to mathematics and physics/science. We certainly need to address that in the primary educational system - high school and below (which are subjects in other threads).

I took 'Modern Physics' 30 years ago. It followed a basic curriculum of Mechanics/Waves, Thermodynamics and E&M during the first three semesters. The fourth semester was Quantum Mechanics/Modern Physics which dealt with phenomenon on the atomic, nuclear and particle levels. The textbook was 'quantum physics' by Eyvind Wichmann (UCal-Berkeley) from the Berkeley Physics Course (Vol 4).

This prepared us for the third year where we tackled Schrödinger's Equation for the hydrogen atom, while concurrently studying Classical Dynamics (using Marion) and E&M (using Lorrain and Corson).

Now importantly, freshman students were expected to take Ordinary Differential Equations (1st sem) and Multivariable/Vector Calculus (2nd Sem), and some could take courses in Analysis. During the second year, one was expected to take courses in Linear Algebra, Complex Analysis and Partial Differential Equations. All of the math courses went in parallel with physics courses.

The problem was that this was an ideal approach that was not really official. Most of it the students had to figure out for themselves. My approach was to read the advanced textbooks and figure out what math courses I needed to understand the physics. As an aside, the year I started studying physics, my faculty advisor was on sabbatical and the department never bothered to assign a new one. I should have gone to the department and asked for a new advisor, but I thought I could handle it myself. Well, I overdid it and burned out by my junior year.

I did not find a strong coordination between the math and physics departments. It would be great if math and physics were taught in a way so as to make both meaningful. Perhaps it is at some school.

edit: Throughout all this, every year while in academia, I purchased at least 2 or 3 supplemental books in math or physics, because the assigned texts were inadequate for my needs. I also spent a lot of time in the library, and often xeroxed sections of texts.
 
Last edited:
  • #30
My preparation was very similar to Astronuc's...

Four semesters of calc-based physics ending with an intro to modern physics : we had 8 weeks of special relativity then the balance of the semseter in modern phyiscs culminating in the Schrodinger equation

As a Junior we took Quantum Mechanics (McGervey, which is a fine book to read and learn from) along with Mechanics out of Marion. Our math preparation thru this time consisted of Calc 1-3, Diff Eqn, Applied Math 1 & 2 (advanced vector calculus, and Fourier series along with PDE).

As as senior we had E&M (Wangsness) and Thermo/Stat Mech (Reif) without any more math preparation.

AS for learning modern physics, it takes time. After earning terminal degrees and haveing 13 semesters of QM at all levels I am still learning the material. Work, work, work is all I can say. One of my old professors said during the first day of graduate QM "Your homework is EVERY problem in this text, each chapter due one week after I finish lecturing. Get working because the only way you are going to learn this stuff is lots and lots of practice." When you do 200 problems during the course of a semester, you'll figure out something. I'll bet I only got 50% of them even close to correct.
 
  • #31
Dr Transport said:
"Your homework is EVERY problem in this text"


Ouch, Dr. Transport, Ooouuuuuucccccchhhhh:smile:
 
  • #32
G01 said:
Ouch, Dr. Transport, Ooouuuuuucccccchhhhh:smile:

I found that if you didn't attempt every problem in the book at one point or another you were short changing yourself. Example: My E&M Professor would assign between 5 and 8 problems per week out of Wangsness equally distributed between even and odd so you could look up the solution in the back to check your answer. Before an exam I would work ALL the rest of the problems in the chapters covered, didn't help though, still only got B's, but I can stil do E&M after nearly 20 years, practice, practice, practice is the only way you will learn something.
 
  • #33
After reading all the replies, it seems that a lot of the people are having similar experiences about modern physics. My friends said that the material covered in class will eventually be learned again later in our physics career...Well, do you think students would be better off without the modern physics class? or not?

Anyway, our class has just took the midterm about a week ago. I spoke to a lot of the people and they said that the general consensus is: everyone fails. My feeling is the same... Anyway, I can't blame the professor, so I guess I will pick a couple more Intro quantum books from the library and begin studying for the final.

My conclusion for this semester of physics is:
Modern physics=the first physics class I've ever disliked.
Classical Mechanics=one of the best physics classes I've ever had. I've finally learned the mysterious Lagrangian formalism.:smile: and the Hamiltonian formalism, non-inertial system and much more will be covered next semester... it's going to be LOVELY!
 
Last edited:
  • #34
So strange to comment on Modern Physics part of the beginning engineering physics courses as being so difficult. Among the three fundamental beginning courses, the modern physics course was both the most enjoyable and most learnable. The Electricity & Magnetism course was the most incredibly difficult and confusing. The Modern course as I remembered gave good very meaninful mathematics to support the topics, making the study of those topics a very reliable study. Maybe the one drawback of the course was that the treatment of quantum physics was fairly light, although much of the supporting topics needed in the development of quantum physics were well presented with good exercises.

If I were to complain of any parts from the fundamental physics courses being difficult, I certainly would not choose Modern Physics; but I would say that the E&M part was the confusing one.
 
  • #35
tim_lou said:
After reading all the replies, it seems that a lot of the people are having similar experiences about modern physics. My friends said that the material covered in class will eventually be learned again later in our physics career...Well, do you think students would be better off without the modern physics class? or not?

As others have said, the Modern Physics course is the survey course that naturally follows the Mechanics and E&M survey courses. In fact, I would say that it is the most important survey course for physics majors and potential physics majors. This is the course where one could learn what the state of the art is... and where tomorrow's physics major can contribute. Without this course or with a poorly taught course, a physics department can easily lose potential majors to engineering or math. Few will slog through another pass at mechanics and E&M (at the intermediate level) to await their first taste of Quantum, Relativity, and Stat Mech.
 

Similar threads

  • STEM Academic Advising
Replies
12
Views
2K
  • STEM Academic Advising
Replies
3
Views
678
  • STEM Academic Advising
Replies
6
Views
1K
  • STEM Academic Advising
Replies
17
Views
2K
  • STEM Academic Advising
Replies
2
Views
1K
  • STEM Academic Advising
Replies
2
Views
2K
Replies
8
Views
1K
  • STEM Academic Advising
Replies
27
Views
2K
Replies
9
Views
974
  • STEM Academic Advising
Replies
4
Views
1K
Back
Top