Recent content by fadecomic

What happens, and why? (This isn't homework, just curiosity.) To be more precise, what would happen to the magnetic field of the magnet if we passed a current through it (assuming it is conductive). Will the current disrupt the magnetic domains? Will the magnetization disappear?

Incidentally, the expected value for the U statistic is (n_an_b)/2, which is easy to prove. So why does the Mann-Whitney test require a statistic that is shifted to a central value of (n_an_b)/2?

I'm reading up on the Mann Whitney test, and I can't wrap my head around one thing. Most of the test makes perfect sense. If two samples come from populations with similar medians, then the sum of ranks of both of those populations should hover around some expected value. The "T" or "U"...

Oh, never mind. I figured it out. Above, y_i is a random draw from the population, not the sample, so by definition, its variance is the population variance, not the sample variance.

Hi, I'm trying to prove to myself that the formulation of sample variance as s^2=\frac{1}{n-1}\sum_{i=1}^{n}(y_i - \mu_y)^2 is an unbiased estimator of the population variance \sigma^2. Of course, I proceed by checking the expected value of the sample variance, which flows smoothly until I...

I should probably clarify that the loop is at x=y=0, and that \rho, \phi, and z are cylindrical coordinates.

Hi, I'm trying to wrap my head around the derivation of the current density of a filamentary loop. On the face of it, the result seems obvious since it involves Dirac delta functions, but it's the rest of the formulation I don't quite follow. The derivation begins by considering a loop of...

Right, I understand all that, and I may have gotten sloppy with notation, but the question is still the same. You're right though. It would've been more proper for me to say that the PE drops back to its original level, not to some absolute zero. Even considering that, what's getting me is the...

That's hard to envision, because the resistor's not really drawing anything, is it? Isn't the battery is the only active agent. This is my confusion. The battery creates a PE/charge difference that's there regardless of load. The resistance of the load controls the number of charges, each with a...

Hi, I am having difficulty understanding why potential must drop completely over a circuit from the high side of the source to the low side of the source. I've seen this statement in several books now with no further explanation other than "it must". Consider a simple dc circuit consisting of...