Recent content by quarky2001

I didn't put this in the Education forum because I feel the level is probably too high. I have a physics degree and an education degree, but due to my inability to tolerate students who simply don't care about learning, I became an electrician instead. My colleagues and I were having a...

Well, think of what happens when there is no current in the disc, and it starts spinning. The moving electrons spinning with the disk see a changing magnetic field, and the corresponding Lorentz force causes them to drift in the disk with some current density \vec{J} . These electrons...

If I recall correctly, that's because the model you're using is actually decelerating, which means that the redshift will be decreasing with time, making \frac{dz}{dt} negative.

I'm manipulating an equation, and I think I am correct in doing this, but not sure. Could someone tell me if the equality I've written below is true? [\nabla\cdot [\rho\vec{v}\vec{v}] ]\cdot\vec{v} = \nabla\cdot[\frac{1}{2}\rho v^2 \vec{v}] (where \rho is dependent on position) *NOTE* that...

Actually, I finally did manage to rewrite it. (although I'm not familiar with Einstein's tensor notation) Assuming my math is correct, the following equality should hold: \vec{v}\cdot (\vec{v}\cdot\nabla )\vec{v} = \frac{1}{2}(\vec{v}\cdot\nabla )v^2

Sorry - I'm not sure what you mean by that subscript notation. I know v dotted with nabla is an operator on the v on the far right, and I know the result will be a scalar. I just don't know how I could re-write that expression in a simpler fashion.

I'm working on simplifying a big physical expression (I don't like the Navier-Stokes equations at all anymore), and I'm curious how to simplify the following term: \vec{v}\cdot (\vec{v}\cdot\nabla )\vec{v} where v is a fluid velocity - i.e. definitely spatially varying. I'm just not sure...

Thanks for the reply - I asked the professor today. He just worded the question funny. By "nearby", he meant that the globular cluster's stars were redder than other stars of similar metallicity "nearby" the solar system, not nearby other stars in the globular cluster!

This is the exact question: Stars in a globular cluster are observed to be one magnitude redder (in terms of B-V color, so the color excess E_(B-V) = 1, and extinction in the V band is 3.1) than other nearby stars having similar metallicity. What causes this? I'm aware of why two stars...

This should be a simple question, but I haven't found a clear explanation anywhere yet. Suppose that there are a bunch of particles in a gas, with their velocities "uniformly distributed over solid angles", and I want to find out what fraction of particles are traveling with velocities in a...

Whoops, forgot that! Thanks for checking it though. It's a shame it doesn't simplify more, but so long as it's correct I'm fine with it.

I'm trying to find the time derivative of the following function, where E is a constant, spatially uniform vector field, and B is as well, but B varies with time. \frac{d}{dt}\left(\frac{\vec{E}\times\vec{B}}{B^2}\right) Remembering that B is time dependent and E is not, I've calculated the...

I think I might have come up with a solution, but I'm a bit unsure, as it came about without as much math as I thought it would take. Given the constant E-field, and the time varying B-field, we know there will be an E-cross-B drift term in the new drift velocity. The other part I think I...

It's an intro plasma physics course, and already starting to get to me... I'm asked to derive an expression for the drift velocity of a particle in a constant uniform E-field, and a slowly time-varying B-field. I've looked at a few books to see if I can even find the final result, so I...

Okay, well challenging relative to other courses... supposing I'm used to 400-level courses. For example, two other 400-level courses I took were "Introduction to Condensed Matter Physics" and "Quantum Mechanics B". Needless to say, there was no comparison between the difficulty of the two.