Field Definition and 1000 Threads

I'm already stuck on A. I'm hoping once I figure that out the rest will just fall into place but be prepared for this to take awhile. I understand how to use Faraday's law to get the current or voltage of the system based off the movement of the bar but I have no Idea how to relate the rate of...

I am trying to derive the expression in components for the covariant derivative of a covector (a 1-form), i.e the Connection symbols for covectors. What people usually do is take the covariant derivative of the covector acting on a vector, the result being a scalar Invoke a product rule to...

My attempt so far: $$\begin{align*} (\nabla_X Y)^i &= (\nabla_{X^l \partial_l}(Y^k\partial_k))^i=(X^l \nabla_{\partial_l}(Y^k\partial_k))^i\\ &\overset{2)}{=} (X^l (Y^k\nabla_{\partial_l}(\partial_k) + (\partial_l Y^k)\partial_k))^i = (X^lY^k\Gamma^n_{lk}\partial_n + X^lY^k{}_{,l}\partial_k)^i\\...

ok probably if one did a lot of these this could be solved by observation others separate the variables and take to Integral to get the equation

Since E_i=0 for the ground state, and $$E_f=\frac{(\hbar)^2l(l+1)}{2I}$$, $$w_{fi}=\frac{E_f-E_i}{\hbar}=\frac{(\hbar)l(l+1)}{2I}$$. So, $$d_f(\infty)=\frac{i}{\hbar}\int_{-\infty}^{\infty}<f|E_od_z|0>e^{\frac{i\hbar l(l+1)t}{2I}+\frac{t}{\tau}}dt$$ My question is in regards to...

Not a homework. Just self-studying electromagnetism. I am stuck at understanding the very beginning of the solution steps in this example: The E as given in the solution is the field away from a long straight line with charge Lambda. That's clearly not the current configuration. E should...

Since there is no charge inside the cone, the total flux through its surface is zero, hence Ø(lateral surface)+∅(base surface)=0. But ∅(base surface)=E.πR².cosΩ, because electric Field is homogenous. But by the figure, Ω is just arctg(h/R). So Ø(lateral surface)=-E.π.R².R/√(R²+h²). This is not...

From Feynman's Lectures, Part I , Ch. 28 Purely in terms of predictive success and useful applications, what kind of physical / practical problems are we not able to calculate because of this gap in our understanding? Have things become clearer in any way, as of 2019?

Hi I'm looking at Tong notes http://www.damtp.cam.ac.uk/user/tong/qhe/two.pdf deriving the Kubo Formula, section 2.2.3, page 54,I don't understand where the Hamiltonian comes from (eq 2.8). I tried a quick google but couldn't find anything. I'm not very familiar with EM Hamiltonians, any help/...

Hey everybody, Background: I'm currently working on a toy model for my master thesis, the massless Klein-Gordon equation in a rotating static Kerr-Schild metric. The partial differential equations are (see http://arxiv.org/abs/1705.01071, equation 27, with V'=0): $$ \partial_t\phi =...

Folks, I'm not sure if this is the correct forum topic for my question, but it seems to be close or related. Question: If you have a wire carrying current then it creates a magnetic field as in the diagram in the link below...

In David Tong's QFT notes (see http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf , page 131, Eq. 6.38) the expression for canonical momentum ##\pi^0## is given by ##\pi^0=-\partial_\rho A^\rho## while my calculation gives ##\pi^\rho=-\partial_0 A^\rho## so that ##\pi^0=-\partial_0 A^0##. Is it...

Homework Statement: This is not for homework but I have an AP physics exam on field lines and am confused about the proportionality between the charges of objects and the number of field lines. Homework Equations: E=(k*q)/r^2 I am struggling with the number of field lines to put based on the...

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Sorry if I am asking in the wrong fashion as I am new. The above questions are easily solvable: 1) U = -μBcos(0) 2) U = -μBcos(180) 3) W = ΔU = 2) - 1) My question is more related to some theory: where is this work/energy coming from since a magnetic force, to my knowledge can't do "work"...

A simple question, I read that the particles in a plasma (protons , electrons) travel along the B field lines in a plasma which I know and they loop around the field lines each in opposite direction (clockwise, anticlockwise ) but both in the same direction. My question then is this. If I have...

For t < 0 , all I can think of is a qualatative " the field is zero because the intensitity is 0 when the burst of light hasn't been emitted yet " For t >= 0 , I've tried squaring the given E and that let's me say the amplitudes are proportional (with a cos^2 term in the mix) But I feel like...

Hi! I need help with this problem. I tried to solve it by saying that it would be the same as the field of a the spherical shell alone plus the field of a point charge -q at A or B. For the field of the spherical shell I got ##E_1=\frac{q}{a\pi\epsilon_0 R^2}=\frac{\sigma}{\epsilon_0}## and for...

Problem Statement : Here's my attempt : * By assuming that the fringing and leakage effects are ignored. I find the flux density , the permeability and the reluctance of the iron , but then I get stuck . Any help would be greatly appreciated .

Firstly, I need to determine what the electric field is causing. Using left hand rule, the force due to the field is acting down the slope. Hence my FBD looks like: Where the two arrows pointing towards the right represent the force due to the field and weight of the cylinder. Since ...

Option B is correct. Using Lenz's law, the direction of current flowing in coil 1 is counter clockwise while in coil 2 is clockwise. Option A is correct. Using Fleming's left hand rule, the resultant magnetic force acting on the both coils is to the left. I am not sure about option C and D. I...

Hi All. Given that we may write And that the Stress-Energy Tensor of a Scalar Field may be written as; These two Equations seem to have a similar form. Is this what would be expected or is it just coincidence? Thanks in advance

I think choice B is correct because when I draw the free body diagram of each object, there are three forces acting on each of them and the resultant force is towards the center. Choice C is wrong because the net field at center is zero. I think choice D is also correct because if the...

Please refer to the screenshot below. Every step is justified with an axiom. Please see the link to the origal document at the bottom. I am trying to understand why the proof was not stopped at the encircled step. 1. Is there no axiom that says ## x \cdot 0 = 0 ## ? 2. Isn't the sixth...

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Hello everybody, Lets say we have an atom with an electron that have a spin. That spin can only pointing in 2 directions, in s_1=\hbar*1/2 and s_1=-\hbar*1/2 and therefore the magnetic moment of an electron is pointing on the opposite site. My Problem here is appearing when whe apply an...

I think the solution to this problem is a straightforward calculation and I think I was able to make reasonable progress, but I'm not sure how to finish this... $$\begin{align*} \vec{P}&=-\int dx^3 \pi \nabla \phi\\ &= -\int\int\int dx^3\frac{dp^3}{(2\pi)^3 2e(p)} \frac{du^3}{(2\pi)^3}...

In a recent test we were asked to calculate the electric field outside a concentric spherical metal shell, in which a point dipole of magnitude p was placed in the center. Given values are the outer radius of the shell, R, The thickness of the shell, ##\Delta R## and the magnitude of the dipole...

Setup: Let ##\hat{\mathbf{e}}_1,\hat{\mathbf{e}}_2,\hat{\mathbf{e}}_3## be the basis of the fixed frame and ##\hat{\mathbf{e}}'_1,\hat{\mathbf{e}}'_2,\hat{\mathbf{e}}'_3## be the basis of the body frame. Furthermore, let ##\phi## be the angle of rotation about the ##\hat{\mathbf{e}}_3## axis...

So I think I do understand how to do this, but the thing is my answers are always incorrect. Will need some guidance/help on this. ##B =\frac{\mu_{0}I}{4\pi}\int\frac{dysin\theta}{r^2} ## ##y = Rtan\phi## ##dy = Rsec^2\phi d\phi## ##B = \frac{\mu_{0}I}{4\pi}\int\frac{dysin\theta}{r^2} =...

Okay, I am not even sure how to startr with this question. But here's my theory: First I will need to the electric field produced by the ring using the formula: ##E = k\frac{\lambda a}{(x^2+a^2)^{3/2}}## After finding out electric field produced by ring, am I supposed to find out the...

I don't know where to start for part (c), I've managed to get (a) and (b). Can someone simply guide me, I think I'm having trouble understanding what the teacher means by just having an x dependance... Does this mean I only work with the x components of the magnetic field and the electric...

I'm having a little trouble understanding how to go about solving this problem. I was in class Tuesday and the hint I got from the T.A. running my discussion section was that : "because the electric field is only non-uniform along the x axis, the electric field will both enter(negative flux) and...

I used the two equations i listed by using B1=B2 and by doing that i ended up finding that N1/N2=λ. However i am not sure if that's the correct answer as λ is just a variable and not an actual number. Do you think it has to be an actual number or is it not really necessary?

This question is motivated by Problem 7.12 in Griffiths Electrodynamics book. I have not included it in the homework section, because I have already solved it correctly. However, I question whether my solution which agrees with the solution's manual is correct. Relevant Equations: $$\Phi =...

If i had a bosonic field ##\phi(x)## and I took the exponential in the following way to get the operator $$W=e^{\imath f \phi(x)}$$ where ##f## is a parameter what effect would this have when acting on the vacuum ##|0\rangle##? Is it analogous to the space translation operator? Will it transform...

What is/are the potential or theoretical effect on electricity due to reversal of planetary magnetic field? Would circuitry continue to function or would knowledge and understanding need re-evaluating as a result of a reversal of our magnetic field on planet Earth? Note: this is not a homework...

So I just wanted to see if anyone could offer some suggestions. So in my mind this seems impossible, in the case of electric field a jump in time derivative of that field would indicated in my mind that electric charge was either introduced or removed from the system instantaneously which would...

Sorry in advance if this question doesn't make sense. Anyway, I am reading a paper about quantum field theory and the Whitman Axioms (http://users.ox.ac.uk/~mert2060/GeomQuant/Wightman-Axioms.pdf), and it describes a field (Ψ) as Ψ:𝑀→𝑉⊗End(𝐷) where 𝑀 is a spacetime manifold, 𝑉 is a vector...

Please help me understand this line from P&S, or point me towards some resources: Why is there another Lorentz transformation acting on the derivative on the RHS? Thanks

Hi! I need help with this problem. I tried to do it the way you can see in the picture. I then has this: ##dE_z=dE\cdot \cos\theta## thus ##dE_z=\frac{\sigma dA}{4\pi\epsilon_0}\cos\theta=\frac{\sigma 2\pi L^2\sin\theta d\theta}{4\pi\epsilon_0 L^2}\cos\theta##. Then I integrated and ended up...

Hi! I need help with this problem. I tried to solve it like this: First I calculated the electric field of each ring: Thus the electric field at a point that is at a distance z from the ring is ##E=\frac{Qz}{4\pi\epsilon_0(z^2+r^2)^{3/2}}##, Thuss for the upper ring, the electric field would be...

Hello, Today I am wondering if anyone can help me quantify the strength of the magnetic field created by a permanent cylindrical magnet. I have been able to find equations online for the strength of the field within the z axis, (ie. the longitudinal length) but I would like to know the strength...

I know that the field inside sample is a combination of the demagnetizing field and whatever applied field you may have. So these two fields together influence how big a field you need in order to magnetize the sample.

Would this also be correct? Or is there something wrong with it? I appreciate all your responses! Snarlie

I'm currently watching lecture videos on QFT by David Tong. He is going over lorentz invariance and classical field theory. In his lecture notes he has, $$(\partial_\mu\phi)(x) \rightarrow (\Lambda^{-1})^\nu_\mu(\partial_\nu \phi)(y)$$, where ##y = \Lambda^{-1}x##. He mentions he uses active...

I was looking at a sphere that has a positive point charge at the center of a sphere with radius R. Now, I understand that the electric field is pointing outwards (in the direction of dA), so $$d\phi = EdA$$ However, I am told that since the magnitude electrical field is the same because the...

What happens to research when a leading researcher passes away? A new study looked at this in the Life Sciences . The study observed that when a leading expert in a field died there was a significant increase in publications by new researchers (with new ideas?). it was also determined that...

I have no idea how to approach the problem using Gauss's Law. I found the electric field using superposition, and it was incorrect. I am assuming you treat the wire as a continuous electric field, and then also treat the pipe as a continuous electric field. I solved for this using...

Since coordinate transformations should be one-to-one and therefore invertible, wouldn’t there be no restriction on pushforwarding or pullbacking whatever fields we feel like (within the context of coordinate transformations)?