Field Definition and 1000 Threads

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When a charged particle moves in a magnetic field, the magnetic field will not work. But when a nail flying over a permanent magnet is attracted by the magnet, the magnet does work on the nail. Can anybody explain why this is so?

From what I understand, electrons are negatively charged, however, I have recently come to learn that electrons also have a spin which creates a magnetic field around each electron. I don't understand how the electron can be a negative monopole, yet have a completely independent magnetic field...

This is not a homework problem, I want to calculate the equation of the magnetic field intensity from the 3 phase currents separated by 120Degrees. The 3 currents are ##I_{{aa}^{'}} = I_M\sin \omega t ; -> eq1 \ I_{{bb}^{'}} = I_M\sin(\omega t - 120); -> eq2\ I_{{cc}^{'}} = I_M\sin(\omega t...

I can calculate the fields generated by the cylinder and the wire but I don't know how to calculate their vector sum to evaluate it at point A. Cylinder field inside: ρR^2/2rε Cylinder field outside: ρr/2ε Field generated by the wire: λ/2πr I should break the fields into components but I don't...

Hello! So I need to find the potential function of this Vector field $$ \begin{matrix} 2xy -yz\\ x^2-xz\\ 2z-xy \end{matrix} $$ Now first I tried to check if rotation is not ,since that is mandatory for the potentialfunction to exist.For that I used the jacobi matrix,and it was not...

I used the concept of electrostatic induction, which would cause the charges in metal ball near the ebonite rod to have +ve charges on end next to rod and a -ve charge on the end touching the other ball. What confuses me is how charges separate on the second ball. The only way these balls can...

Hello! I am suspossed to write (sketch) this particular vector field. $$V2(r) = \frac{C}{\sqrt{x^2+y^2+z^2})^3} * (x,y,z) $$ Note that the x y z is suspossed to be a vector so they would be written vertically (one over the other) but I don't know how to write vectors and matrices in LaTeX,so...

[New poster has been reminded to show their best efforts to work the schoolwork problem when starting a homework thread] My question is : An electron beam with velocity vector v = (0; 0.6x10^8 ;0) m.s enters between two oppositely charged plates parallel to the xz plane. - How large is the...

I'm not quite sure where to start. If someone could help me I would very much appreciate it.

I'm given an ultra-high energy cosmic ray with energy 10^20 eV. It is coming from a source 10 Mpc away with an extragalactic magnetic field with strength B = 10^-9 G. I am to determine the maximum angular deflection of this cosmic ray, so it hits Earth. I don't have an attempt of the solution...

While classical mechanics uses single action optimizing trajectory, QM can be formulated as Feynman ensemble of trajectories. As in derivation of Brownian motion, mathematically it is convenient to use nonphysical: nowhere differentiable trajectories - should it be so? Can this connection be...

Summary:: Can a moving object cause disruptions in a magnetic field that could be detectable? Hello, I was hoping someone could assist me on a query I have regarding disruptions in a magnetic field. For some context, I am creating a science fiction story which features a non-humanoid alien...

Hi, I tried to solve this exercise but I'm not sure about the process. First of all, I imposed that "K = E": so that "v = √ ( (2q ∆V)/m))" then I replaced in "r = m v / (| q |B)", v with "√ ( (2q ∆V)/m))", and found out that R = (2√(2)) r. Then for the second point, I imposed Lorenz Force...

Hi, I was practicing some problems on the magnetic field and the electromotive force, when I got stuck on these two exercises. Could you help me figure out how to proceed? In the first problem, I tried to find the magnetic field flux by multiplying the induced current for ∆t and R. Should I now...

For a real scalar field, I have the following expression for the field operator in momentum space. $$\tilde{\phi}(t,\vec{k})=\frac{1}{\sqrt{2\omega}}\left(a_{\vec{k}}e^{-i\omega t}+a^{\dagger}_{-\vec{k}}e^{i\omega t}\right)$$ Why is it that I can discard the phase factors to produce the time...

Why is the energy of a circuit placed in a magnetic field at infinity zero?

Hi guys ! I am taking phys102 course .I figured out that i didnt fully understand the concept that is the Voltage. Please look at this question. In this case we can see that there is no voltage in point C and there is no electric field is in point D and as you know V=U/q .So i always thought...

In QFT where the electromagnetic field is mediated by virtual photons, is it possible to describe the larmor precession of an electron as a series of emission and absorption of virtual photons? how does the spin angular momentum "evolve" over a series of events? This feels like a challenging...

I am only asking about part (b)(i) and (b)(ii). Below is the explanation for (b)(i). What is going on in the above? I understand up till the 3rd line, about the left/right hand circular motion. What is the "upward motion" the solution mentioned? Is it suggesting that ions are moving...

Hello! Lately I've been experimenting with the ways an electromagnet effects a Rare Earth magnet. The electromagnet we used was taken from a vibrator massager, probably 50s vintage. The resistance of the coil is 96 ohms and consumes about 1.25 amps when operated on 120 volts AC. When the...

I am a little confused why my answer is wrong... Briefly, my answer is as follow: $$P = \epsilon_{0} X E = (\epsilon-\epsilon_{0}) E; \space \space \space \space \space \space \space E = P/(\epsilon-\epsilon_{0})$$

So what I'm not sure on, is calculating the matrix elements for part (iii) with Pauli spinors and Pauli matrices, and then finding the form of the corresponding states. As I don't see how using the hint helps. The following is using the eigenvalues of the spin-operators. Provided what I...

For a solenoid, magnetic field at the centre = ##\mu_0nI##. I see the argument on why at the opening at the ends of the solenoid, the B-field is ##\frac12\mu_0nI##. Apparently, B-field is ##\frac12 \mu_0nI## at the sides of the solenoid too. (ie at/within the wires that make up the solenoid)...

In Theoretical Minimum: Quantum mechanics, Leonard Susskind describes an electron in the higher energy spin state in a magnetic field radiates a photon of energy ##\hbarγ|B_0|## and flips into the lower energy spin state. I am wondering if this photon is related to the "virutal photon" that...

I understand that negative charges create electric fields pointing inwards, and positive charges create electric fields pointing outwards, but what does this have to do with field stength? What is the relationship between field strength (flux?) and direction?

weight/mass = gravitational field strength. my working is -> weight = 150kgx10m/s² = 1500N mass = 150kg gravitational field strength= 10N/kg. is this correct?

A massless scalar field in a curved spacetime propagates as $$(-g)^{-1/2}\partial_\mu(-g)^{1/2}g^{\mu\nu}\partial_\nu \psi=0 .$$ Suppose the gravitational field is weak, and ##g_{\mu\nu}=\eta_{\mu\nu}+\epsilon \gamma_{\mu\nu}## where ##\epsilon## is the perturbation parameter. And let the field...

Will translation parallel to x-axis work ? Else please suggest the symmetry? And does symmetry here refer to the symmetry of the sheet which causes the symmetry of the field or something else? Please be kind to help.

Our class modified an experiment to measure the magnetic field strength in mT between 5cm and 30cm, and I have plotted data and found that the relationship resembles a power relationship (using a log vs log graph). In order to find the percentage uncertainty for the whole experiment I need the...

I used a couple ways to do this question, but I got neither correct. Can someone help, please? Thank you. 1. E= V/r = 700 / (60*10^-3) = 11667 (very far from the given answer) 2. E = (-kQ/r)⋅ dr = kQ/r^2 = kQ/ [( 1/20/ 10^-3)^2 - (1/80/10^-3)^2] (For this method, I stuck...

In string theory, physical states satisfy QBΨ = 0, where QB is the BRST operator. This equation of motion can be obtained from an action S = ∫ QBΨ*Ψ + Ψ*Ψ*Ψ There is a gauge invariance under δΨ = QBΛ. what is the framework in which the role of the BRST operator QB is understood in open string...

I find a exercise in Leonard Susskind's book Classical Mechanics the Hamiltonian of a charged particle in a magnetic field(ignore the electric field) is $$H=\sum_{i} \left\{ \frac{1}{2m} \left[ p_{i}-\frac{e}{c}A_{i}(x) \right]\left[ p_{i}-\frac{e}{c}A_{i}(x) \right]...

Hi! I have been looking at differential forms, manifolds and de Rham cohomology. Now I'm trying to figure out the connection from cohomology and equations of motions and topological field theory. Problem is that I am only looking at abelian field theories and I only find introductions into...

I have been analyzing a set of data from a lab activity on the Zeeman effect. The data (i.e. images) gathered can be previewed via this Google drive link here. While I am provided with the numerical data on the current (##I##), I am not provided with any data on the magnetic field. With the...

https://www.physicsforums.com/attachments/282201 Are we using this equation above to explain this question? The magnetic field is definitely in sinusoidal form but how does it proportional to the frequency of the source?

I used the equation below and the attachment to rationalize. https://www.physicsforums.com/attachments/282163

Torque appiled by smaller disc = mga emf of disc due to B = Bwr2/2 Current I = Bwr2/2R force = IBr = Bwr3/2r torque = rF = Bwr4/2r mga = Bwr4/2r

So I was wondering, can a moving electric field produce a drag force on gas for example similar to that which would result from physical blades moving the gas. Electric field applied to a dielectric if not as strong as to produce breakdown produces polarization. I wonder can this polarization...

I am confused about why spin down has a lower energy than spin up. What is the correct interpretation of the equations? If we have a spin ##\frac{1}{2}## particle in a magnetic field ##B_0## that is applied in the positive z direction The spin states of the particle are $$\ket{up} =...

I have the following lagrangian density: $$L = \bar{\psi}i \gamma^\mu \partial_\mu \psi - g\bar{\psi}(\sigma + i\gamma^5\pi)\psi + \frac{1}{2}(\partial_\mu \sigma)^2+ \frac{1}{2}(\partial_\mu \pi)^2 -V(\sigma^2 + \pi^2)$$ where $\pi$ and $\sigma$ are scalar fields. I have show that this...

Please help me on this question I have tried to do it many times but I end up getting the wrong answers. I have show my work what I have done.

I have a toroid with square cross section and 2 different circuit: ##C_1## where ##N=N_1## and ##I=I_1## ##C_2## where ##N=N_2## and ##I=I_2## I have a question that say I have to find the magnetic field ##B## produce by ##C_1## everywhere inside the coil. I assume here I have to find the...

I know how to derive field using ##E = -\nabla V## in polar coordinates and doing so gave me $$E = (kP/r^3)(1 + 3cos^3\theta)^{1/2}$$ now I am trying to derive ##E## at point P using the fields produced by +ve and -ve charge respectively and taking components of each along the radial direction...

Hello, I would like to present my situation and maybe hear some suggestions on how to overcome the challenge I am facing: I have a PhD in a STEM field from Canada (I am an immigrant), and after I received my PhD, I worked 18 months in the academia as a postdoctoral researcher. During my...

Why the equation of state parameter w for a quintessence field with potential m²Phi² is not in between 0 and 1/3 depending on the energy of its particles relative to the mass of the field instead of the w resulting from formula 9 of https://arxiv.org/pdf/1504.04037.pdf which seems to be...

Background Information (Not Strictly Necessary): As a quick recap, the graph I am dealing with is a semi-logarithmic graph of free induction decay (FID) amplitude as a function of time. To acquire the value for ##{T_2}^*## (and its uncertainty) in the graph, I used the below equation to do so...

I identified $$(\Phi_{SN})_{*})$$ as $$J_{(\Phi_{SN})}$$ where J is the Jacobian matrix in order to $$(\Phi_{SN})$$, also noticing that $$\frac{\partial}{\partial u} = \frac{\partial s}{\partial u}\frac{\partial}{\partial s} + \frac{\partial t}{\partial u} \frac{\partial}{\partial t} $$, I wrote...