Recent content by BearY

Homework Statement Introduction to Electrodynamics (4th Edition) By J Griffth Ch.4 Problem 4.18 The space between the plates of a parallel-plate capacitor is filled with two slabs of linear dielectric material. Each slab has thickness a, so the total distance between the plates is 2a. Slab 1...

If you have a distribution of mass, you may find a point where g = 0 through simple math. The question is do you have a distribution of mass? Probably not.

Did you just... I mean, you answered the 2nd and the 3rd question yourself.

How about this: You will tell me what you know about Friedmann's solutions. And I will see if I know enough GR to help you.

Yes after a night's sleep I realized ##m\times B = 0## implies ##m_1 \parallel m_2##. Since the dipole term can be written as ##B=\frac{\mu_0}{3\pi r^3}((m\cdot \hat r)\hat r - m )##. If the second term does not become 0 after cross product with ##m_2## that would mean porjection of ##m## on...

Thermal radiation is just a fancy way to say photon emission in this case.

Would Stefan–Boltzmann law suffice? As for how long, It will always emit photons. As long as T > 0K.

Just for the record, The text is Introduction to Electrodynamics (4th Edition) by David J. Griffiths Chap.6. What does "when the magnetic dipoles are aligned" mean? Does it mean Both moments are parallel to each other's magnetic field? i.e. ##m\times B = 0## for both? Or is it ##m_1\parallel...

Heh maybe that's why ##\oint## is used :-p I am a sheeple and I am good as long as I know the convention is what I think it is.

In many texts I have seen, Gauss theorem has the form of$$\frac{q}{\epsilon_0}=\oint\vec{E}d\vec{A}$$ Why a line integral symbol was used for this surface integral everywhere? The more I see it the more I believe there is something wrong with my understanding about this. I didn't think too much...

If the radial dispersion velocity is too large then the system is probably no gravitational bounded, because then the kinetic energy of most of the galaxies in the cluster would be enough to escape? If it is very slow too slow I can't think of anything else except that it can be bounded...

Homework Statement Estimate how long a galaxy in the Coma cluster would take to travel from one side of the cluster to the other. Assume that the galaxy moves with a constant speed equal to the cluster’s radial velocity dispersion. How does this compare with the Hubble time, t H ? What can you...

Actually never mind, the question asked for z component only, I can't believe I overlooked it and spent 2 hours on this.

Homework Statement A charged sheet with charge density ##\sigma## is described by ##-\infty<x<0,-\infty<y<\infty, z = 0##. Find the electric field at ##(0,0,z)##. Homework Equations Electric field of continuous density charged body from the Coulomb law: $$E = \frac{1}{4\pi...

When I was studying vector calculus we only did parameterizing dimention x, y, and z with t and then integrate w.r.t dt only. So without parameterization, we still integrate each dimension separately? That makes sense. I suppose I will have to redo vector calculus to know for sure.