What don't I know?

January 26, 2011 7:16 PM

Out of my depth in a physics class, what do I need to study to catch up?

I was last in school a... while ago, and though I passed an introductory calculus class, it was never my best subject. I'm currently in a physics class which I was told uses 'a bit' of calculus, but that '[you] don't need to worry about it'.

So, for an example of our second assignment, we need to:
Use Wien's Exponential Law to derive:
-Wien's Displacement Law
-Stefan's Law

I will link to a scribd thing that I found which has these equations in it [on page 22]

I won't be able to do this assignment [successfully] for sure, but what sorts of things do questions like these assume I know how to do?
I have a few calculus textbooks and 2 physics books that cover similar subject matter, but I am overwhelmed by my inability to even know what process I don't know how to follow.

I have a few weeks to figure out if I should abandon ship, but I'd really like to just put in some extra effort and catch up. I enjoy [and have no problems with] the concepts discussed in the lectures, but I lack the calculus skills to even understand what to do here.


So... I guess I'm asking for some sort of assessment of what kinds of skills I'd need to do things like this. I hope that's not too vague of a request.

What don't I know here?

posted by Acari to Science & Nature (8 answers total)

Go talk to your professor asap. Try to be clear about what you're having trouble with and see if he can make recommendations on how to get up to speed. Do you know any of the students in the class? Try to get involved in a study group...preferably with students that know what's going on, not students that are struggling too. If you have a bit of cash then you could also consider a tutor until you've got your physics sea legs. Physics classes move pretty fast because there is a lot of ground to cover so I'd suggest being pretty aggressive in getting help if you want to stay in the class.
posted by victoriab at 7:27 PM on January 26, 2011

General advice about university courses where you're feeling a bit stuck or confused -- step 1 is to make use of the resources you have on campus! Do you have teaching assistants for the course? Email them and ask what they recommend, or arrange a time to meet and they can help walk you through things on paper. Is there a math/science tutoring center on campus? Go! Definitely make use of those types of resources, including going to the professors' office hours with a few clear-cut questions to ask, or ask how he/she would recommend studying for the course. Maybe you can form a study group with other students in the course? You want to be sure you're using every tool available to help you succeed before you decide to abandon ship.
posted by LobsterMitten at 7:28 PM on January 26, 2011

This sounds like a second year Modern Physics course, right? They'll say you don't need much calculus for it, which is technically true, but you're going to need to be familiar with the concepts. Are you at least familiar with what a derivative means, and how to do straightforward ones?

I'd say that even if there isn't difficult calculus in the course, you're going to want to be pretty comfortable with 1st year level math to get through it easily.

Professors have a tendency to say "don't worry about the math, the math is easy" for just about any course, because, well, the math is easy... to them. Not so easy to us mortals.

I stay stick with it, but ask lots of questions.
posted by auto-correct at 7:30 PM on January 26, 2011

To add to the "get help from TAs" answer, ask the TAs to give a list of math concepts for the whole year in advance, so that you can find appropriate resources and also have time to catch up. Otherwise, for every new concept you encounter, you will have to repeat the process.

My sympathies - physics classes can be really difficult.
posted by theobserver at 8:34 PM on January 26, 2011

If there is a math tutoring lab at your school (and there should be, I'm pretty sure they all have them) this is one place to go for help on your calculus skills (and the tutors are probably pretty used to helping with physics problems, too).
posted by Green Eyed Monster at 8:34 PM on January 26, 2011

I won't be able to do this assignment [successfully] for sure, but what sorts of things do questions like these assume I know how to do?

i think you're faking yourself out a bit here... the first derivation exponential -> displacement looks like it's probably a straightforward min/max problem for the exponential law. i think you need to just make clear to yourself in english what this derivation is asking you to find i.e. what do the two wien's laws say in english rather than math. this should tell you what math you need to do.

the 2nd derivation might involve a three-dimensional integral and gauss's law to go to a surface integral or vice versa just from glancing at the wikipeda article

but mainly, i don't know how they do things in canada, but the derivation of stefan's law will likely be in a book somewhere, if not wikipedia. go find a solution, understand it, and write it up from the beginning doing every step. don't copy straight out of where you found, but make sure you understand it on your own.

also. it's not going to get a whole lot better, you need to find study partners who can explain things to you when you are stumped and give your moral support. these mid level physics classes can be really brutal because they require you to regurgitate answers to material whose foundations you really can't be asked to understand.... i.e Q.E.D. or even classical statistical mechanics. my point is that you can drive yourself totally crazy if you try to actually understand this material on a fundamental level. the best way to probably learn the calculus you need is to try to work through derivations from a book or try to solve this problem. starting in at some calc. textbook will likely waste time and frustrate you.
posted by ennui.bz at 8:44 PM on January 26, 2011

just to continue: problems like this that ask you to 'derive' formulas can be really cheezy, they are either totally elementary in a tricky formulation, or require you to play fast and loose with something.

i'm not into trying to figure out the stefan's law derivation right now, but it might not even require three-dimensional calculus if you can state the problem clearly.

so i guess my advice is really: make sure you really understand what each of these laws are in english and what it would mean to derive one from the other and this will tell you what math to do. or there could be a dirty trick somewhere.
posted by ennui.bz at 8:50 PM on January 26, 2011

Don't know what forms of the laws your class is using so it might require less or more, but some things you might need to understand to do this particular problem:

• The concept of a derivation — roughly, how to use mathematical techniques to change an algebraic relationship into a different form that expresses a related algebraic relationship
• Standard rules of differentiation (first-year calculus, first semester)
• Multivariable methods of integration, e.g., knowing what it means to integrate a function over the sphere and having some memory of how to do it (first-year calculus, second semester)
• Substitution of a dummy variable or function as an integration technique (first-year calculus, first and second semester)
• Possibly the knowledge of how to do a numerical integration, or how to find the value of a standard solved integration in a book of look-up tables or an equation solver like Mathematica

For the problem itself, take a look at

• http://planetphysics.org/encyclopedia/WienDisplacementLaw.html (the Planck law is similar to the exponential form of Wien's law)
• http://en.wikipedia.org/wiki/Stefan–Boltzmann_law (has the derivation from the Planck law)

For most people, I can't imagine taking a second-year modern physics class with only a background of one introduction to calculus class taken a long time ago. If you took the full first-year sequence and were pretty comfortable with it at the time, I'd say stick with it for a couple weeks and try to get through the rustiness before deciding whether to drop it. But it makes me a little nervous for you that you don't have an idea of where to begin. Math/science tutoring resources on campus are a great idea, but only if you've actually taken the math you need to get through the class.

Definitely talk with the class TA about what background the class requires and how to go about doing the homework problems. If you're still completely at sea after being walked through homework solutions and there's no sense of "oh, it's starting to come back to me," you may need to drop.
posted by hat at 9:05 PM on January 26, 2011