What is Electromagnetism: Definition and 838 Discussions
Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force is carried by electromagnetic fields composed of electric fields and magnetic fields, and it is responsible for electromagnetic radiation such as light. It is one of the four fundamental interactions (commonly called forces) in nature, together with the strong interaction, the weak interaction, and gravitation. At high energy, the weak force and electromagnetic force are unified as a single electroweak force.
Electromagnetic phenomena are defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as different manifestations of the same phenomenon. The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. The electromagnetic attraction between atomic nuclei and their orbital electrons holds atoms together. Electromagnetic forces are responsible for the chemical bonds between atoms which create molecules, and intermolecular forces. The electromagnetic force governs all chemical processes, which arise from interactions between the electrons of neighboring atoms. Electromagnetism is very widely used in modern technology, and electromagnetic theory is the basis of electric power engineering and electronics including digital technology.
There are numerous mathematical descriptions of the electromagnetic field. Most prominently, Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.
The theoretical implications of electromagnetism, particularly the establishment of the speed of light based on properties of the "medium" of propagation (permeability and permittivity), led to the development of special relativity by Albert Einstein in 1905.
Homework Statement
Homework Equations
Let e be electric field.
e=kq^2/r^2
Fe=qe
The Attempt at a Solution
I have no idea what the steps to solving this are, I am looking for a quick outline on the first few steps only.
I calculated the magnitude of each point's electric field at 0.144.
Homework Statement
I'm given an equilateral triangle of side length b with charges q at each corner and I have to find the y coordinate for point P on the y-axis where the electric field is equal to zero (E=0 other than the center of the triangle)
2. The attempt at a solution
I figured I'd...
Homework Statement
[/B]
The total force on a moving charge q with velocity v is given by \mathbf{F}=q(\mathbf{E}+\mathbf{v}\times\mathbf{B}) Using the scalar and vector potentials, show that \mathbf{F}=q[-\nabla\phi-\frac{d\mathbf{A}}{dt}+\nabla(\mathbf{A}\cdot\mathbf{v})]Homework Equations...
How is a continuous chain reaction maintained within a moderator if it is not fissile material? Are the fissile materials mixed with the moderator or are they coalesced at the center of the surrounding moderator? If it is the latter, how would the surrounding moderator allow fissile material to...
Homework Statement
Use a computer to calculate numerically the potential energy, per ion, for an ifinite 2D square, ionic crystal with separation a; that is, a plane of equally spaced charges of magnitude e and alternating sign.
Homework EquationsThe Attempt at a Solution
The closest I can...
Hi! I am new to the forum and need a little of help in a science experiment
I wanted to ask you which of the following catapult systems will be more accurate and efficient:
1. Weight as the source of energy. The weight at the bottom of the beam moves back, the beam will go forward and the...
Given a system of two charges (+7q and -q) some of the field lines will terminate at -q while others go on towards infinity. I've read that the portion of the field lines that terminate is given by (1/7), but I have no idea why that is. I am supposed to find the maxium angle of a field line...
there are no electromagnetic waves? All I know is that there is a modified version of the Maxwell equations (in differential form) for such a universe, such as (the arrows represent vector arrows):
→∇x →B = μ0 →j + μ0 ε0 ∂→B/∂t instead of having ∂E/dt in the last term (which would be the case...
Hi, I'm trying to figure out how the current density for a poloidal current in toroidal solenoid is written. I found you may define a torus by an upper conical ring ##(a<r<b,\theta=\theta_1,\phi)##, a lower conical ring ##(a<r<b,\theta=\theta_2,\phi)##, an inner spherical ring...
Hi, I'm trying to write the current density for such circular loop in spherical coordinates. For a circular loop of radius a that lies in the XY plane at the origin, the current density it's simply:
\mathbf{J}= \frac{I}{2\pi\sin\theta}\delta(\theta-\frac{\pi}{2})\frac{\delta(r-a)}{a}\hat{\phi}...
Suppose that a ferrite bead is put around a cable where a constant current I flows, just like in this image.
The coordinate system has the z axis along the cable. Let's evaluate the current through the (x,y) plane: according to the Ampère's law, the only magnetic field component generated by...
Homework Statement
Two points charges.
q1=2.4e-6 C is located at (0,0)
q2=-5.7e-6 C is located at (3,0)
I must calculate the magnitude of the Electric field at (0,0)
Homework Equations
E=kq/r^2 ; k=9e9
The Attempt at a Solution
The electric field at (0,0) due to q2=9e9x(-5.7e-6)/3^2 =...
I'm doing an experiment on the effect of the speed of rotation of a rare Earth magnet on the voltage generated in a solenoid coil. I was wondering, how does rotating the magnet affect the magnetic field?
The experiment setup is similar to the one below:
Earnshaw's theorem http://en.wikipedia.org/wiki/Earnshaw's_theorem gives a straightforward reason why we can't have a static equilibrium for a system of point charges. For some time I've been trying to find out if anyone's worked out a similar proof for the impossibility of a dynamic...
Hello all,
While I understand the significance of natural units, I am wondering why, in SI units, we are able to assign μ0 an exact value. The speed of light is experimentally determined in m/s, and given the relationship derived from Maxwell's equations, we know that c^2 = 1/√(ε0μ0). Thus by...
Homework Statement
Can we consider the universe to have a uniformly charged distribution?
If so, shouldn't the field at any point in space be zero? Since the universe is infinite, will it be symmetrical about any point, field should be zero right? Why is this not true?[/B]2. The attempt at a...
Hi there!
I am currently building a simulation to model the propagation of radio waves in seawater in terms of its propagation loss. I have previously discussed the models I've looked at but have settled on a model which depends primarily on the propagation distance ##r##, the carrier wave...
Before I start, I apologise for the information dump that is to follow. I don't expect all questions to be answered or all models to be addressed; I simply feel it is appropriate to provide the community with my current knowledge and stage of research so you may not have to search for it...
Homework Statement
Hi all, I would appreciate some help with the following problem;
I need to obtain and visualize the current flow and magnetic field profile of an elliptic cylinder (made from ferromagnetic material) which has a left section set at 0 volts and a right section set at 5 volts...
Hello!
I have in my notes an expression for the sheet resistance of a uniform conductor with length L, width W = L and thickness t. It is
R_{\square} = \displaystyle \frac{\sqrt{\displaystyle \frac{\pi f \mu}{\sigma}}}{1 - e^{-t/\delta}} = \displaystyle \frac{1}{\sigma \delta} \frac{1}{1 -...
Hi all,
I am designing an NFC device but am still a little unsure about the principles behind NFC/RFID. From what I understand:
A primary coil constantly emits a 'carrier frequency' magnetic field.
This field induces an e.m.f. on a passive secondary coil which is in a secondary circuit.
The...
As far as I'm aware of, a lot of models in particle physics and in the so called grand unified theories postulate the existence of magnetic monopoles.
When I was an undergraduate student I always thought that it was fascinating that so much could be built theoretically without the CONCRETE...
Hello everyone.
I've built a Helmholtz coil and I'm attempting to understand how the magnetic field direction and magnitude will be effected do to a material with a particular permeability.
In the first picture I have an infinitely long cylinder with a particular thickness and permeability...
Well, I am a bit confused. Griffiths himself writes in his book "Introduction to Electrodynamics" at one point in his book that this law is "simply wrong". In a footnote, he writes that it was wrong in principle wheras it is true for non-relativistic speeds, and later on in his book, he goes on...
Electromagnetism: Multivalued potential voltage?
It's been my understanding that specifying the electric and magnetic potential at all points in a system determines the electric and magnetic fields--and more, that we can fix a particular gauge, and it all still works.
Perhaps I've been naive...
Hi guys. I have just finished my first year as an undergrad and I still think I don't know enough E&M ( took half year course and I barely passed the final exam).
Can you please recomand a good textbook to study over the summer?
Hi, I'm looking for some great books clearly explaining how electricity, magnetism and electromagnetism Works.
I'm also looking for some books describing how it was discovered and what experiments have been performed in discovering how it Works,.
So Far I've looked at
Electromagnetism...
Homework Statement
I am having difficulty understanding the very first step of the following solved problem (I understand the rest of the solution).
How did they obtain the expressions for ##\hat{n}## (the direction of polarization), and ##\hat{k}## (the unit vector pointing in the direction...
Homework Statement
I came across a recent problem that asked me to calculate the flux density at the end of a solenoid. I was given the current 3 A , the number of turns per unit length , 12 cm-1 and the using the permeability of free space as 4π × 10^-7
Homework Equations
The equation I used...
In my lecture we were discussing the Lagrangian construction of Electromagnetism.
We built it from the vector potential ##A^\mu##.
We introduced the field tensor ##F^{\mu \nu}##.
We could write the Langrangian in a very short fashion as ##-\frac{1}{4}F_{\mu \nu}F^{\mu \nu}##
In the end we...
Homework Statement
I am working on a problem that states the following:
Imagine an infinite straight wire carrying a current I and uniformly
charged to a negative electrostatic potential Φ
I know here that the current I will set up a magnetic field around the wire that abides to the right...
Hi,
I am working on an experiment to investigate the effect of electrical conductivity of the metals on the levitating force produced.
Basically the concept is this: when a metal plate is placed on top of a solenoid (but not touching), as the a.c. flows in the solenoid the change in magnetic...
Homework Statement
Problem 6.2 of Griffith's "Introduction to Electrodynamics": Starting from the Lorentz force law ##\vec F=\int I (d\vec l \times \vec B)##, show that the torque on any steady current distribution (not just a square loop) in a uniform field ##\vec B## is ##\vec m\times \vec...
I am an undergrad student and i have been through a first easy course on electrodynamics and i have used the book of Griffiths which let me satisfied.But the next two courses i will be taking are notoriously hard mathematics-wise so i want a step-up from Griffiths.I want a mathematically...
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)...
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...