Magnetic field Definition and 1000 Threads

Hi all, I've recently become transfixed with the idea of magnetism and gravity. I have two main questions I'd like to see discussed more. 1. Would it be possible to harness magnetic fields for energy on earth/for acceleration between planets? 1a. Has this been studied at all? 2. Why do we...

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...

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

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...

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...

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 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]...

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?

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

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 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...

Hi, I have to find the magnetic energy inside a coaxial cable of inner radius ##a## and outer radium ##b##, ##I = I## By using Ampere's law if ##r<a## ##B = \frac{\mu_0Ir}{2\pi a^2}## if ##a<r<b## ##B = \frac{\mu_0I}{2\pi r}## if ##r>b## ##B = 0## Then, the energy in a magnetic field ##E_b...

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...

Basic descriptions of spin such as the beginning of Lindley's "Where does the weirdness go" state that an electron's spin doesn't exist or is "indeterminant" until measured (e.g. passed through a Stern-Gerlach field). However, isn't the magnetic field nonzero essentially everywhere (albeit...

Hi, I have to find the motion of a particles ##(x,y,z)##. However, I'm not sure where to begin. Is it correct to split the problem and first find what's the motion in the x direction then y and z. For exemple, ##m \frac{d^2x}{dt^2} = -kv_{0x} + qv_{0x}B sin 90 ## ##m\int\int...

I attempted to run a lab that would allows us to calculate the magnetic field strength of a couple different neodymium magnets. I would love some feedback on it and ways that I could potentially make it better. The numbers I calculated were very far off from what I expected. Apparatus set up: I...

The force on a charged particle that is moving through a magnetic field is explained in introductory physics textbooks. The magnetic field cannot change the kinetic energy of the charged particle because the force from the magnetic field is always perpendicular to the velocity, so no work is...

here is the question, don't mind about point (a) and (b) because i have solved them already...the main problem is the question on point (c) : so far, what i have done is : H = 2.7*0.1-(1.4*0.15+1.3*0.25) = -0.265 az A/m which is the wrong answer compared to the solution provided from the...

I calculate like this and I think the answer is E not D. N( µoI/2a + µo2I/2*2a) = 2µoNI/2a = µoNI/a

I haven't taken a physics courses in some time and I'm having trouble getting started with this textbook question. I know that there will be relativistic effects present, but I can deal with that. The problem is how I can approach the problem. I initially thought of a geometric way to set up...

A global environmental crisis 42,000 years ago https://science.sciencemag.org/content/371/6531/811

So force on a current carrying wire = ILxB. If I have a bunch of bar magnets making a uniform magnetic field of strength B, then a 1 meter long wire of 0 ohms carrying 1 Amp, the force on that wire is (1)(1)xB = 1B. If I let that force move the wire for a time T, let's assume the wire moved a...

On a previous thread (now locked) I was wondering about how, precisely, the Earth's magnetic field protects us from the solar wind. Posting this here because what I wrote in that thread is very wrong, and I think it's an interesting topic. I had a hell of a time finding good information. I...

So my idea was that to reach the equilibrium position, the final moment of force has to be 0 (so in the end the forces will “eliminate” each other). And I found the equation Fm=B*I*l*sinα, which should characterize the force, which affects wire with the current in a magnetic field, and Fleming’s...

I have some difficulties in solving this problem. This is what I did. I wrote down the equation of motion for the masses. For the first point \begin{equation} m\ddot{\textbf{r}}_1=\textbf{F}_1=q\dot{\bar{\textbf{r}}}_1\times...

We know that when a magnet is exposed to high temperatures, it loses its magnetic properties. Why then does the Earth's magnetic field behave differently? That is, why doesn't the Earth lose its magnetic properties? According to BBC News Brasil, the core temperature is around 6000 ° C, higher...

This should be pretty straightforward and my take gives B = 0.000193*T for a) and B = 0.00000063 T for b). Or have I misunderstood something?

In this lecture Lenny Susskind describes a spin in a magnetic field precesses around the axis of the direction of the magnetic field. This description is also frequently found in NMR theory which is a semi-classical theory. Lenny says if the magnetic field ##B_o## is applied in the ##z##...

If you take a horseshoe magnet and fuse the north and South Poles together (without destroying the magnetic field) would you have a “pole-less” magnet? And if so, what special properties would it have(other than other magnets)?

I was reading some papers about calculating the magnetic field produced by a coil using the biot savart law and I saw some graphs that caught my attention. This one from a paper from Ravaud, et al. Titled "Calculation of the Magnetic Field Created by a Thick Coil". I saw similar graphs in...

I got stuck near the beginning, so I tried working backwards. Starting from B = (k X E0)/ω * cos(k⋅r - ωt +φ) I found -∂B/∂t = -k X E0 sin(k⋅r - ωt +φ) So now I need to find ∇ X (E0 cos(k⋅r - ωt +φ)) and see that it is equal to the above result. This is where I'm stuck though, I'm not sure...

Assume a solenoid coil(made up of ##N## windings) placed in the horizontal(##\hat{y}##) direction and in a constant uniform magnetic field. Would an induced current run through the(closed) coil if it spins around its central horizontal ##\hat{y}## axis? My guess is "no", since such a current is...

Hello people, in a near future I'd like to calculate (numerically, with finite elements) the magnetic field of several permanent magnets of various shapes. I am wondering which equation(s) I should solve, exactly. It's been a long time I dived into an EM textbook and I don't have one in hand...

A thought experiment: A electron is moving in a straight line at velocity v. It instantly stops dead. It doesn't move another femtometer. Obviously its magnetic field collapses and produces light. What is the waveform of the light produced? Is it something like this...

Here this is my attempt : Reference Textbook : Zangwill's Modern Electrodynamics I stuck at the last step , I really have no idea what to do next.

Hi all, I interested in how can I get low of motion in for orbiting particle in a uniform magnetic field $$\frac{d\vec{r}}{dt} = \vec{\omega}\times\vec{r},\qquad \vec{\omega} = \frac{e\vec{B}}{mc},$$ Of course, rotating about z' axis is very simple. \begin{equation}\label{eq:K}...

So I'm confused what the Saturation Flux Density is referring to. Defintion says it is when you no longer get an increase in H-field when increasing external B-field. So, does the satuation flux mean the core can only create fields UP TO that saturation flux, or that it can make a stronger...

I'm looking for an estimation or simulation of the magnetic field in the horizontal plane just above a typical lens in a transmission electron microscope. A rough cross section of such a lens can be seen here: electron lens - Bing images . The lens is cylindrically symmetric around the vertical...

Hi everyone, I'm currently working on the problem listed above. I'm pretty new to electrodynamics, and I'm learning on my own through a book. I was wondering if someone can please help me through this problem. Here are my thoughts:I think I need to use Faraday's Law of Induction for part (a)...

I understand that because the vectors are perp, k x i = j, but why is k x j = -i? Why the minus? Could you please explain?

Suppose there is a charged line and near that line, there is a magnetic needle lying in the vertical plane of the line. The magnetic needle is radially placed. If the charged line and the magnetic needle are moving at a same constant velocity(parallel to the line, v<<c) towards an observer. I...

Hello folks, I'm working on a question as follows: I appreciate that there might be more sophisticated ways to do things, but I just want to check that my approach to the line integral is accurate. I will just give my working for the first side of the path. So I have set up the path as a...

This problem honestly got me in big confusion. I managed to find the angle ##\theta## at which the rod rests by equalling the components of weight and Lorentz's force... but from this point on I really don't know how to manage the harmonic oscillation part.