Electromagnetism Definition and 853 Threads

First this Q might be trivial thus apologies. Consider two bar electromagnets that can simulate bar magnets M1 and M2, placed end to end at distance D apart (North Pole of M1 facing South Pole of M2). Magnet M1 is 'fixed' to a base. Assuming both electromagnets have the Current I1 and Voltage...

The definitions of D and H are: ##D=\epsilon_0 E+P## ##H=B/\mu_0-M####P=\epsilon_0 \chi E## ##M=\chi H## I was wondering, if E and B are the fundamental field relating to all charges/currents, why is the definition of the polarisation the opposite for each of them? So why is H in the...

Hey everyone! I am supposed to calculate the energy contribution of the magnetic field term of an electromagnetic field. Basically the term is the following: \int_\Omega dx^3 (curl(\vec{A}))^2 And we can use the following two equations for simplifying: div(A)=0 and \Box A=0 So basically...

Homework Statement I've not been able to do this question for years so I'd really appreciate some help. Light is normaly incident from a medium 1 with impedance Z1 through a layer of medium 2 of thickness L and impedance Z2 into medium 3 of impedance Z3. Obtain an expression for the total...

Considering the above diagram, I am failing to see why the aluminium ring floats upwards rather than oscillates. I understand Faraday's law, but I am struggling with Lenz's law - as there is an alternating current, an alternating magnetic field is produced, similar to a sine wave. Therefore, I...

I have looked in vain on the web for pictures of magnetic field lines for multiple linked current loops. I would be happy just to see a picture of the field lines for a simple Hopf link but somewhere there must be pictures for the Borromean rings and other more complex links - and also braids...

I seem to have a fundamental misunderstanding of the principle here. in the previous part it was required to sketch the graph for the hall probe. I knew since the speed was constant the field was cut at a constant rate hence a straight line was needed. However I did not understand why it...

Hi, so I've just started learning about physics and I get the gist of most of it. I understand motion, torque, energy, light, radioactivity. But there is one topic that absolutely stumps me. Electricity. Can someone explain to an absolute moron like me what it is? It seems like everyone around...

Hi, I am planning to conduct an experiment using electromagnet but I could not find the soft iron core. My school lab doesn't have it, and I tried asking around in shops which sell electrical appliances and shops which sell science apparatus but nobody seems to sell it. Does anyone know where...

The way I have interpenetrated this phenomena without technical jargon is that: Light is basically waves or ripples of the + and - charges of the electromagnetic field which permeates the entire universe. This is very similar to sound rippling through a field of air molecules. These waves can...

Look, I found that there exist two kind of electric current: conventional flow and electron flow. I have read that in every situation I have to use the conventional flow, however I'm going to work with electric circuits using copper wires. In solids, only negatively charged particles (electrons)...

Whenever a charged particle is in motion ,there is both electric and magnetic fields created. Why is it that we only study one of it at a time ?

I know that \oint \vec E \cdot \vec{dS} in Gauss Law indicates electric flux. \oint \vec E \cdot \vec{dS} = \frac{Q_{enc}}{\varepsilon_0} But what does B.dl indicate in Ampere's Law? ##\oint \vec{B} \cdot \vec{dl} ## = ??

Homework Statement You have a spring of length l, radius R, with N loops and n loops per unit length. If you consider it a solenoid, what current do you need to apply to withstand a mass m hanging from it, without stretching or shrinking the spring. Homework Equations Magnetic field inside a...

A changing electric field produces magnetic field and vice versa.Does that mean that this process will carry on forever?Think of a circuit with a capacitor.The magnetic field due to the current at a point on the wire(with Ampere-Maxwell law).But current was changing with time,so it also meant...

Homework Statement If you have a ring of charge, is it valid to say lambda = Q/L, or is it lambda = dQ/dL? Homework EquationsThe Attempt at a Solution

Why is the drift velocity of an electron in a wire defined as: tau*(E*e/m) and not 1/2 *tau* (eE/m) as it is the AVERAGE VELOCITY!? because the above defintion of drift velocity is the velocity that is attained before the collision so rather the maximum velocity of the elctron, isn't it?

Homework Statement Good afternoon, How can you mathematicaly talk about how how group theory compares to electromagnetism. Homework Equations e^iθ=Cosθ+iSinθ The Attempt at a Solution I know that the above formula is because of a sin wave and a cosine wave. Put them together and you get a...

I stumbled upon this article: http://www.comsol.com/blogs/exploiting-symmetry-simplify-magnetic-field-modeling/ Since the article does not contain any mathematical formulations, I was wondering how the boundary conditions can be expressed in terms of magnetic vector potential. From what I...

Hey all, I realize a question on this topic has been asked elsewhere, but the links to references they use seem to be dead, so I'll press on! I'm reading some introduction to antenna theory and I've often puzzled on the equation: A_{eff} = \frac{\lambda^2}{4\pi} which relates the effective...

Hi all, I'm a Usman,a physics student from Pakistan .I have joined this forum to polish my physics skills and to share whatever I know about physics ,its principles and so many on......:smile::smile::smile::smile::smile::smile:

I have a question about magnetic repulsion. Suppose I have a permanent magnet (axially magnetized) placed on top of the iron core of an electromagnet. I want to switch on the elctromagnet to repel the permanent magnet. (Please assume the permanent magnet is contained in some kind of tube that...

When you have a metallic ball hanging from a electromagnet and you disconnect the electromagnet, there is a delay between the moment you unplug the machine, and the ball starts falling. Why does this happen?

I always heard that magnetic forces don't do work, and that they act perpendicularly to the direction of movement.

1. The problem statement, all variables and given/known Two long parallel vertical wires 0.3m apart are. ' placed east-west of one another. The current in the westerly wire is 30A and on the other 20A. The horizontal component of the Earth's magnetic flux density is 2*10^-5. Find the force per...

I'm a mechatronics engineering student, and I know that electronics is a requirement in most engineering programs. I'm been dealing with electronics recently and I've been studying electric circuits. I've been noticing that in some of them instead of being closed (in diagrams) they are like...

hi, everyone I didn't know where to post this thread so I posted it here. I have read many articles about EM wave to find what I'm searching for and nothing still. I have seen many pictures, animations and videos about EM wave, and about oscillating charge, but still nothing. What I am really...

Homework Statement Suppose I am undertaking an experiment using a scanning electron microscope in which there is a positively charged plate underneath the target sample. I want to find the change in energy of the electron due to a positive voltage on this plate from the point it leaves the...

Homework Statement One of the three types of radioactive decay is "β decay", during which protons decay into neutrons or viceversa, emitting either electrons (β) or positrons (β+) at high velocity as a result. In one experiment, a β source and β+ source are placed 10 cm apart from each other...

I have some doubts about minimal coupling of a field of spin 2 for example, with the electromagnetism and I hope someone can help me to clarify them. According to Pauli and Fierz one couples the field with electromagnetism introducing the covariant derivative at the level of the Lagrangian...

Hello there, people! I am quite new here; in fact, this is my first post. I am quite strange to this place. Feeling kinda welcome, though. Okay, so short to the point. I am an 8th grader, and my school just started teaching us about electricity. Well, the basics. I knew much about it, much...

Can anybody explain me relation between timetravel&maxweels theory

Since light, a form of electromagnetic radiation, gets bent in a gravitational field even though it does not have any rest mass, it is obvious gravity is a force that does much more than just attract two masses towards each other. Since it affects electromagnetic radiation, it has led me to ask...

Homework Statement Two charged particles (P & Q) are fired into a uniform magnetic field that is directed into the page. When a particle possessing charge q moved through a magnetic field B at a velocity v it experienced the lorentz force that has a magnitude of F=qvB. What is the sign of P...

I know we can represent it two different ways. First: \mathbf{B} = \frac{\mu_0}{4\pi}\int_C \frac{I d\mathbf{l} \times \mathbf{\hat r}}{|\mathbf{r}|^2} If we open up unit vector, then it becomes: \mathbf{B} = \frac{\mu_0}{4\pi} \int_C \frac{I d\mathbf{l} \times \mathbf{r}}{|\mathbf{r}|^3} I...

The formula for Helmholtz coil is given by mu*(0.8^1.5)*nI/R, where I is the current, n is te number of coil and R is the radius of the coil. Now assume the bunch of coils have a small 'thickness' w (so it looks like a hollow cylinder with a very small height), and the the two coils are...

We know Total Magnetic Flux B = B_0 + B_m Where, B_0 is the external field and B_m is the field inside a material. Now, we get, B = B_0 + μ_0*M (M is the magnetization) My question is - Do I always have to use μ_0 ? If yes then Why? The material isn't free space, is it?& also B =...

Homework Statement These are actually two problems that I'm merging into one because each of them seem to have conflicting solutions, and I want to clear this up. Consider a long cylinder (very long) extending in the z direction with a constant magnetization ##\vec{M}=M\hat{z}##. What are the...

I'm looking for history books on the beginnings of physics (mechanics, electromagnetism, etc) focused on explaining the evolution of the various fields that we have nowadays in physics more than trying to introduce them. For example, I'm looking for books that talk about how Newton discovered...

I was under the impression that an emf is the work done per charge by any source that is not electrostatic. However, there are such things such as emfs produced by varying magnetic fields. Being that magnetic fields never do work, what is an appropriate way of thinking of an emf?

In Feynman Lectures on Physics (you can find it online), chapter 33 of volume 1, the author derives Fresnel's formulas for the coefficient of reflection in an unusual way by making considerations about the different possible polarization of light. In this way he derives the squares of the...

I was under the assumption that a magnetic field acts similar to that of the normal force in mechanics; both affect the path of the object, but do no work. So now suppose that we have a rectangular circuit with the left side in an uniform magnetic field that is pointing towards the computer...

Homework Statement (a) Find the four-vector potential of a moving charge (b) Find source time and z-component of electric field (c) Find electric potential to first order of x and hence electric field[/B] Homework EquationsThe Attempt at a Solution Part(a) [/B] \phi = \frac{q}{4\pi...

Homework Statement (a) Find faraday tensor in terms of ##\vec E## and ## \vec B ##. (b) Obtain two of maxwell equations using the field relation. Obtain the other two maxwell equations using 4-potentials. (c) Find top row of stress-energy tensor. Show how the b=0 component relates to j...

I'm delving into AC as well as attempting to understand the various wave forms used in electrical engineering, and I am curious how engineers are able to generate current which alternates in a sinusoidal manner. What specific phenomena allows us to achieve this? Is it a special circuit, or does...

Well, recently I have started to deal with electronics and I've seen several new concepts such as ohm's law, parallel and series circuits, what's AC and DC and many other topics. Ok, I have no doubt on what's direct and alternate current or what a series and parallel circuits are; rather than...

Hi all, My question is, in electromagnetism, magnetic field intensity H is equivalent to electric field intensity E , right?? Now, definition of E says that E is the force experienced by an unit positive charge in an electric field created by a source charge. So what is the definition for...

http://en.wikipedia.org/wiki/Jefimenko's_equations What is the integral in these equations called? how do you integrate over (d^3)r'?

I have 2 questions about those 2 equations. 1-) Which one came first in the history of electromagnetism? Some articles say: Biot-Savart derived their equation from Ampere's Law. Some say: Ampere derived from Biot-Savart. Which one is true? 2-) Since Ampere is special form of Biot-Savart and...

This is Newton's law of universal gravitation. $$F=G\frac{m_1.m_2}{r^2}$$ Gravitational field $$g$$ is derived from this formula $$g=G\frac{m_1}{r^2}$$ This is named gravitational "field" strength. If Newton knew nothing about "field concept" and formulated his formula in the form of "action...