## Search found 15 matches

Thu Apr 02, 2009 6:34 am UTC
Forum: Science
Topic: Magnets and Their Fields!
Replies: 7
Views: 1089

### Re: Magnets and Their Fields!

As others have already pointed out, magnetic fields do obey superimposition. However, for a magnetised object placed into a uniform field, you either have to specify the magnetisation of the object (the tractable by hand case is uniformly magnetised sphere/long rod... this is the problem of a perman...
Thu Apr 02, 2009 6:21 am UTC
Forum: Science
Topic: Physics, quantum mechanics
Replies: 8
Views: 1188

### Re: Physics, quantum mechanics

You can also recall, that to have a mutual eigenstate for two operators A and B, [A,B]=0. (they must commute).
Fri Dec 12, 2008 6:09 am UTC
Forum: Science
Topic: Physics GRE
Replies: 13
Views: 22193

### Re: Physics GRE

I got rejected from the top-tier (Berkeley, Harvard, Stanford, didn't bother with Caltech or MIT). I had a similar GPA, two publications and a higher GRE score (not much higher, 80 something percentile). (Also domestic student). I got accepted into all schools I applied to that were as good as UCSB ...
Fri Oct 17, 2008 11:04 pm UTC
Forum: Science
Topic: Magnetic Field by Rotating Sphere
Replies: 5
Views: 7992

### Re: Magnetic Field by Rotating Sphere

This is a good problem. It gets a little tricky evaluating the integral though, you have to whip out some fancy or clever tricks that you may have never used before. For the current density, you want to use: current = (charge density) * (angular velocity) x (radial position vector) where the x is a ...
Tue Aug 12, 2008 4:38 am UTC
Forum: Mathematics
Topic: Something I've been wondering since 7th grade
Replies: 22
Views: 4562

### Re: Something I've been wondering since 7th grade

Taking the logarithm gives you the behavior you'd like (with the usual caveat about what sort of numbers you can take the log of):

ln(xy) = ln(x) + ln(y).

it is a very useful property.
Thu May 29, 2008 4:45 am UTC
Forum: Science
Topic: Help me save my REU
Replies: 4
Views: 1319

### Re: Help me save my REU

I think you're freaking out. 8 weeks is a long time to spend focusing on one thing. REALLY focusing, not like how the usual coursework can be skated through. You've got two months of full time work to try figuring out how to model a 1d plasma. Teach yourself the simplest 1d model currently out there...
Sat Feb 16, 2008 4:53 am UTC
Forum: Mathematics
Topic: Eigenvalues of a special case matrix help
Replies: 20
Views: 2802

### Re: Eigenvalues of a special case matrix help

Hahaha, I'm glad to see my question has spun off. Actually, I poorly phrased the question in the beginning. It is the nearest neighbor lattice problem if you take A and B to be the same all the way down. And the solution you guys found is the familiar eigenvalues. The case I was actually thinking ab...
Fri Feb 15, 2008 5:02 pm UTC
Forum: Mathematics
Topic: Eigenvalues of a special case matrix help
Replies: 20
Views: 2802

### Re: Eigenvalues of a special case matrix help

Nathanielj You're right about the characteristic equation. (I investigated it by picking a few particular N and seeing what pops out, and I do get a polynomial with only the odd powers). However, what is this permutation definition thing you speak of? Honestly, I had 4-5 weeks of Linear algebra in u...
Fri Feb 15, 2008 4:54 pm UTC
Forum: Mathematics
Topic: Eigenvalues of a special case matrix help
Replies: 20
Views: 2802

### Re: Eigenvalues of a special case matrix help

http://en.wikipedia.org/wiki/Tridiagonal_matrix would help i think, although as your case always has 0s on the diagonal it should be slightly simpler again what sort of lecture was it btw? Ah, yes, I knew there was a name for a matrix of this form. That was one of the things I was hoping to be remi...
Fri Feb 15, 2008 5:00 am UTC
Forum: Mathematics
Topic: Eigenvalues of a special case matrix help
Replies: 20
Views: 2802

### Eigenvalues of a special case matrix help

Hi everybody, I'm trying to figure out how this trick was done in lecture once. I've never had a proper linear algebra class, but I sort of use it here and there anyway. We have a NxN matrix (Where N is odd). The diagonal is 0. The elements are most easily described by: a ij = A d i,j+1 + B d i,j-1 ...
Sat Jan 12, 2008 6:55 pm UTC
Forum: Science
Topic: Banana Stacking
Replies: 10
Views: 1898

### Re: Banana Stacking

Obligatory:

I got your banana hammock right here....

On topic:

I am trying this apple + banana ripening method in my fridge as we speak. There's about 4-5 red delicious apples bagged with 4-5 greenish bananas. As of last night anyway.
Thu Jan 03, 2008 7:42 am UTC
Forum: Science
Topic: [PHYSICS] Alfvén waves!?
Replies: 6
Views: 1250

### Re: [PHYSICS] Alfvén waves!?

The reduction to the 1d case is what I was thinking, but I don't think it's the way to approach this; it makes sense for part B (which you got wrong; assuming B=0 breaks the problem. It's non-dispersive normally), but not part A. There's a rather limited amount of information on spherical standing ...
Mon Dec 31, 2007 7:12 am UTC
Forum: Science
Topic: [PHYSICS] Alfvén waves!?
Replies: 6
Views: 1250

### Re: [PHYSICS] Alfvén waves!?

My superficial answer would be to just work it out like a guitar string problem, ignoring that we're even dealing with a spherical object and ignoring that the boundary field might not be zero. So, just force it to be a standing wave through the diameter, with nodes on each end. This is a standard i...
Thu Dec 06, 2007 8:14 am UTC
Forum: General
Topic: Prove You Are Real
Replies: 167
Views: 15682

### Re: Prove You Are Real

Ok -- first you need to define "real." However, taking just the colloquial meaning of the word, I offer the following points: First, you've already acknowledged our existence in a sense by directing a request towards us. How could you direct a request towards something that doesn't exist i...
Thu Dec 06, 2007 8:06 am UTC
Forum: General
Topic: Who the dickens are you?
Replies: 10922
Views: 2380307

### Re: POST HERE FIRST - INTRO THREAD THE THIRD

Hi everybody, new here. Been lurking a while here and there, now I will be able to act out more often on my urges to post. I suppose I'll edit in more info, as most of these posts are much more detailed. I'm a physicist to-be (I don't know when I can start officially start calling myself that, perha...