Okay, guys. I passed Physics I and II (intro classical mechanics and intro electromagnetism), but only because I memorized a bunch of equations and methods of solving the problems. I only barely passed the second class because all the other students were retarded and the teacher applied a huge grading curve. I don't feel like I've learned any physics. Physics right now just seems like a big mess of equations; no intuition.
How do I become less shit at physics? Or am I just retarded?
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I also just finished Physics I and II. Passed with an A and B, but I feel like I only received such grades due to the other areas of the class, such as homework, labs, etc. Quizzes and finals I sucked complete ass. I feel pretty dumb.
Going to watch this thread.
Read books. Git gud at math. Do exercises. Don't be discouraged about having to memorize the equations, you shouldn't be deriving them every time you have to use them. And special cases and solutions using things like Legendre polynomials and Bessel functions took many man hours to solve, don't feel discouraged if you need to memorize those or don't understand when or how to use them at first.
The solved examples in books are usually problems that explain the basic concepts of the topic and should be taken as basic fact and the intuition built around them.
Give an example of what you felt like you haven't learned or are missing from your education.
OP here. I also got those same grades. I'm not ashamed of them, obviously, but I still don't feel like I've learned any physics.
>Give an example of what you felt like you haven't learned or are missing from your education.
Well, one of the biggest sources of my frustration was not fully understanding the physical significance in the equations. This was especially bad in electromagnetism, since the concepts seem more abstract, like fields, voltage potential, etc. Doing problems came down to finding the equations that have the right terms and plugging and chugging without any understanding of the concepts underlying those equations and why they are useful for solving that particular problem. Yes, it is discouraging to memorize equations without understanding their connection to the physics.
As for an example, take any of Maxwell's equations.
>his was especially bad in electromagnetism, since the concepts seem more abstract, like fields, voltage potential, etc
Easy stuff. You see the electromagnetic potential is actually just (the pullback of) a connection on a U(1) - Principal bundle fibered over the spacetime manifold, which means the electromagnetic field itself is just the curvature of said connection.
Dont worry. You are supposed to feel like this in the beginning, I know I felt like that.
What comes next will start to put some hair in your chest, and before you know it, you will use knowledge you didn't even knew you could use.
Just don't make my mistake and go hard from the start.
Yeah, I know what you're getting at. It's not stuff that can be easily understood at this level. It's still frustrating to mindlessly plug stuff in to equations you barely know anything about.
So should I just chug along and hope I'll eventually understand?
Electric field is just force per coulomb of charge. Voltage difference is how much energy a charge gains per coulomb.
READ READ READ
(physic/math that is)
Specifically a good place to start is Feynman's lectures on physics to round out the conceptual side.
>Voltage difference is how much energy a charge gains per coulomb.
*charge gains along the path, per coulomb. Voltage is potential energy per coulomb.
>Electric field is just force per coulomb of charge.
Of course that's the definition. What does that mean, physically? Or is it just a completely abstract concept that has no physical meaning or connection?
If a charge is placed at a position that has an electric field, E, it's force at that instant would be qE. You determine the electric field from free charge by Gauss' law, which is hard to solve for non-symmetric geometries. If instead you wish to determine the electric field from certain voltage boundary conditions or geometries, you solve Poisson's or Laplace's equation. These are also hard to solve for strange geometries. Poisson's and Laplace's equation are solved more often [most likely by FEM], since what we usually control in a lab setting is the voltage on an electrode.
The E field is not just some abstract concept, since the propagation and intensity of light depends on it (as well as the B field). IIRC the potentials V and A are more fundamental since there are experiments with electron diffraction that are effected by the A potential even though no B field in the area exists. Can't remember the name of the effect.
*You determine the electric field inside a certain space
I can't find any useful resources on Legendre Polynomials
Do you know of any? I have a 1000 page textbook on that kind of stuff but it only covers Legendre transformations
Not off the top of my head, no. Most of the textbooks I used just mentioned them as a solution to a certain example problem without any explanation as to why or how they were derived. They're just solutions to a specific form of differential equation that comes up often enough. There are resources online that show how to generate the polynomials, though. Just search Legendre polynomials in google and you'll find some.
I thought the final exam is easy because its AC RLC circuit analysis and ray diagrams. Easy peasy compared to fucking magnetism.
I haven't read it but there is a book called a student's guide to maxwells equations that is supposed to be good.
I received a 30% or so on my final. :X
(Coming from the guy who you quoted)
It seems like you dont have enough mathematical background
Actually once you understand the proof of stokes law you understand all oft em
>Physics I and II (intro classical mechanics and intro electromagnetism),
Hey, what are some good textbooks for learning this stuff? Like, what are the canon texts?
Giancoli is a fantastic textbook and I was advised to use it to study for the Physics GRE by multiple professors and my internship mentor.
Does Maxwell's equations ever get used in practical circuit design or is it just theory circlejerking?
My guess is they would be applied in capacitor and inductor/transformer design but would generally provide little meaningful analysis beyond the component level.
>Hey, what are some good textbooks for learning this stuff? Like, what are the canon texts?
Young & Freedman - University Physics with Modern Physics
Haliday, Resnick, and Krane - Physics I & II
Read a slightly more advanced book like Kleppner & Kolenkow and Purcell & Morin
I also used this book. It's quite simple and outlines the steps for solving problems. Also has a lot of practice problems.
MIT Prof. Walter Lewin posted his entire lectures as videos online. I swear I sucked at physics and going through his lectures made me not only understand basic physics, but get the confidence to pursue much higher end physics and math. The reason good universities produce good students is not because they are harder, but because the professors teach so well that the content is easy. I now have a PhD in Geophysics and it's pretty much thanks to this guy.
Use a better book or wherever you got the graphic from. That isn't Coulomb's law.
I wouldn't worry about it too much.
Coming to terms with mental retardation is something a lot of people have to go through.
>How do I become less shit at physics?
Understand rather than memorize. Nothing in physics is arbitrary, but it may take some thought to grasp.
Also practice. Working problems is the only real way to build intuition.
I am well aware of MIT's OCW material, and I agree with you completely. The professors at MIT are superb. Makes me kinda jealous sometimes.
>That isn't Coulomb's law.
Yeah, I just pulled a random image off the Google.
I'm just trying to be a little less retarded than I am right now, f a m.
Kinda hijacking this thread :
I failed EM I despite getting perfect or almost perfect grades in the other courses and know I need to learn the material for re examination. Our proffesor is really shitty (he's a very smart man but awful at teaching) and he also has a book on this course. In his book, when it comes to Gauss law, he somehow justifies using it even when the charge is exactly on the surface. I've read that part numerous times and I have no idea what the hell he's doing, I've looked elsewhere and always people say that you can't use gauss law for charges on the surface.
Any thoughts?
ask him
>Or am I just retarded?
Don't be too hard on yourself. Get a tutor, read from different sources and practice!
Would you recommend going through Lewin's lectures or through Khan academy for the first time learner?
Honestly, it depends on your level of math understanding. Lewin's classes are calculus-based while khan academy tends to be more trig based. If you have a strong calc background, go to Lewin's. If not, go to khan academy, then proceed to lewins for further learning. Make sure to have an intro textbook near you
I am wondering do physics courses like this ever get better?
Do you ever get to a level comparable to a high quality courses in the world?
one possible way to better understand equations is to give them context e.g. historical context. for example do you know how or why gauss bothered to come up with the equations in your pic? how did it change other areas of study? to understand these contexts either read the biographies of mathematicians and physicists and the histories of their fields leading all the way back to the greeks. academics may disagree with my advice because it will not improve your skill in math or physics, therefore to them may seem like a waste of time. however gaining meaning can easily make these subjects seem more real, more profound. popular science media, while simplified, can also explain context. since its simplified you dont need to go too far deep into fields that ultimately have nothing to do with you but they still give you context.
Understand these, understand everything.
Physics is very simple in the end, it will click eventually.
> Smart
> Awful at teaching
Pick one.
if you are smart, you are also smart enough to figure out how to be a good teacher.
What's your own reasoning for why he should be mistaken user
>implying its impossible to be smart and have trouble with something moderately difficult
>Does Maxwell's equations ever get used in practical circuit design or is it just theory circlejerking?
You need them for more complex systems. The reason we use component theory is so we don't have to use Maxwell's equations every time. You use them to justify a simple way of transformer and magnetic circuit design, although it's only valid up to the magnetic saturation point. Air core inductors you'd use Maxwell's equations, although it's just solving for the magnetic potential A to find the distribution of the B field. That ends of being mostly FEM territory. If you wanted a capacitor that doesn't have any parasitic inductance you be mindful to use a foil rolled capacitor and instead use a purely parallel plate capacitor. Component manufacturers take that into consideration.
More complex systems like particle accelerators or magnetrons or plasma physics or w/e, you need them. Also if you want to model wave propagation you use them in FDTD numerical approximations.
You do use it for charges on the surface, to the extreme approximation that the closed gaussian surface integral follows the surface closely. IOW when you use it, you make a gaussian surface that is a rectangular prism which encloses the conductor's surface with the height of the prism extended out of the surface infinitesimally small, such that the E field flux is considered parallel to the surface of integration. It's used to justify the parallel plate capacitor equation C = A*epsilon/d and also the E field between the plates of a capacitor. You also use it to justify some boundary value conditions at the junction between two materials.
>mindful to use a foil rolled
mindful not* to use a foil rolled
he is really smart, I mean he's the dean of the best faculty of physics in my country, there is a good amount of scroll on his uni page, tons of research, conferences, seminars, lectures, he makes problems for the international physics olympiad, you get the picture.
but he is awful at teaching, there are a few smart people in my class and none of them got anything out of his lectures, I talked to (smart) people from previous generations and they are saying the same thing, they had to learn the material totally on thier own.
well he uses a solid angle approach to justify gauss law results, and it makes sense when you have the charge inside the gaussian surface, it also works when you have it outside the gaussian surface, but when you have it exactcly ON the gaussian surface he goes on and says something along the lines of:
"so the angle under which the closed surface can be seen from one of its points is equal to half of the entire solid angle" and he concludes that in this case the flux due to a charge on the gaussian surface through that surface is the charge divided by 2 epsilon. I mean wtf nigga, this dosen't make sense to me and seems handwasy af. Also I tried looking at other resources and found nothing about the flux due to charges on the gaussian surface
I don't think you understand what I meant, see above ^^
The charge has to be inside the gaussian surface. It doesn't make sense for it to be on the surface since the field would be infinite, unless special geometry cancels it.
yes, exactly, that's what I said, that's what other people from my class thought, but in his book that's how it's presented.
I remember this being confusing but a better way to think about it is this: If you find an infinitesimally small section of the surface it will look flat the same way the earth looks flat to us. Because of this when you look around half of your field of vision will be occupied by the sky (outward) and half of it by the earth (inward). So the flux is half of what it should be if it was inside because each charge "sees" only half of the surface. This is what your prof is saying about the solid angle.
This is also a bit handwavy but maybe it helps.
yeah, but here is what I don't understand:
you need the flux through that surface, so you need the electrical field to be well defined in every point. but the electrical field is not defined for r=0, i.e. on the charge. you may say that you can get infinitesimally close to the charge, but that dosen't help, as you need the surface to be closed in order to apply gauss law, and if you take out the point where the charge lies on the gaussian surface, you can't apply gauss law, as the surface is not closed, you broke the math behind it
This is the best response. I had zero to no intuition about spins until I learned that Sp(n) is just the metaplectic cover of SO(n) with representations on a finite international Hilbert space. Everything became so clear afterwards.
I never heard of it being used in 3D but it can probably be fixed using Lebesgue integration. The Lebesgue integrals of two functions which are equal everywhere on the interval, except for a finite set of points, are equal.
I'm guessing you haven't heard of it if you just finished Physics II but it's very intuitive, a single point (or rigorously a set of measure zero) won't contribute anything to the surface under the graph. Generalizing to 3D, the value of the field in the charge doesn't matter because it's only one point and it won't affect the whole surface integral.
yeah, I know that, but my problem is with the whole "closed surface" thing.
I mean, if you take 1 out of [0;1] you end up with and OPEN interval, [0;1), isn't this the same thing as taking out the point where the electric field isn't definde out of the gaussian surface? now you can't use gauss law results because you don't meet the requierments
the part with Lebesgue integration may be the way to go, but I don't know much about them except that they exist
What problem/geometry is he using Gauss' law for?
I'm not sure I understand what you're asking
it's about finding the flux of the electric field through a closed surface. The "geometry" is the usual euclidean space.
That isn't an open interval.
>it's about finding the flux of the electric field through a closed surface. The "geometry" is the usual euclidean space.
How is the charge distributed? Is there a conductor there? Why would he even talk about putting it on the edge of the gaussian surface, or is he just saying you can do it? What's the motivation? You said the charge is on the surface, is it a point charge, sheet of charge, etc?
I don't see the point in him bringing it up.
I had the opposite problem. I suggest looking at the diagrams and read about how the science was first discovered.