Recent content by asdf60

I'm kind of self studying from Griffiths's QM book, and I'd like to clarify a few things I find confusing. As I understand it, for any potential V, there can exist bound states or scattering states. In the case of the bound states, the solutions to the time-independent schrodinger equation are...

nothing is really missing, you just have to make a few assumptions. you have the time the ball takes to fall, and hence assuming g, you know the velocity as it hits the steel plate. You also know the velocity as the ball leaves the steel plate upwards, so you know the change in momentum from...

never mind, I'm an idiot.

Problem 1.17 in griffiths gives, at time t = 0, the state psi =A(a^2-x^2) for -a to a, and 0 otherwise. It asks then to find the expected value of momentum p at 0 and also the uncertainty in p. How do I do this? The only way momentum is defined is md<x>/dt, and since the state is only for time...

This thread is slightly related to another question: https://www.physicsforums.com/showthread.php?t=109211 I was hoping someone here could give a better explanation since it's essentially a relativity problem. In general however, what exactly does it mean to say that information propogates...

I'm quite aware of this. I've seen the derivation, but the derivation I saw doesn't satisfy me (from purcell's E&M textbook). I was hoping that someone could provide a better derivation or explanation.

Yes, that's correct. What I really mean is this: Say, for example, there is a star, 15 light years away, moving uniformly very fast relative to me and in a transverse direction (that is not along the line of sight). Now any time I see the star, the star is in fact (15 years * velocity of...

Consider a uniformly moving charged particle (moving along the x-axis say). Consider an observer a light minute away from the origin, on the y-axis. Now, when the particle crosses the origin, the observer measures that the electric field points towards the origin. Why is this? This seems...

It's a little meaningless to ask then if 'he' stops moving, since 'he' is not really defined. In reality, he (and the train) deform during the course of the collision.

Right! I quickly dismissed that idea because I thought that it assumed d(x) doesn't change sign, but i realize now after thinking for a second that it's only necessary that f(x) doesn't change sign, which of course we have control over. Thanks for the help, and sorry for wasting your time.

I don't think we'd be allowed to use gaussian functions. I don't even really know much about them. however, i was thinking about doing something like that, but i still don't quite know how to prove that the integral of d(x)*f(x) will start to be less than 1...

Unfortunately, that is not the way the function is defined in this problem. The definition given is: \int_a^b \delta(x) f(x) dx =f(0) where a = -1, and b = 1, always. Heh, i can't figure out how to make the limits of the integration -1 and 1 in latex.

How can I prove that no continuous function exists that satisfies the property of the dirac delta function? I thought it should be pretty easy, but it's actually giving me quite a hard time! I know that the integral of such a function must be 1, and that it must also be even (symmetric about the...

what about for something like a conducting volume, where the charge is distributed over the surface (and hence density is in terms of area not volume)?

How exactly does one find the potential energy of a charge distribution? More precisely, how does one get over the 1/r term in the integral goes crazy near r=0? Purcell says it is possible, but I'm not seeing how for an continuous distribution this is possible. Consider for a line of length L...