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
Consider a glass plate of refraction index n and thickness ## \Delta x ## placed between a point monochromatic source S and an observer O, as in picture.
(a) Prove that, if absorption from the plate is neglegible, then the effect on the wave received by O is the add of a...
Homework Statement
The problem statement is simply to find the vector potential inside and outside an infinite wire of radius R, current I and constant current density j using the Poisson equation.
Homework Equations
The Poisson law can be written A = μ0 /4π *∫(I/r*dl) or A = μ0 /4π *∫(i/r*dV)...
The magnetic force is defined as ## \rm F_e = Bqvsin\theta## and the magentic flux is defined as## \rm \phi = BAcos\theta##
My question is since we are multiplying the two vectors, why is ##sin\theta## used in one equation and ##cos\theta## in second given that ##\theta## is the angle between...
hi
i was wonder as to why when an solonid is placed with a current within and magnet there's a an rotational force. why is it that he difrence in strength of magnetic field created results in an rotation
many thanks
Ewen
Okay, so in Griffith's introduction to electrodynamics, Griffith clearly defines surface current density as follows:
"when charge flows over a surface, we describe it by the surface current density, K. Consider a 'ribbon' of infinitesimal width dL running parallel to the current flow. If the...
Hi, I want to find an equation for the force generated by a solenoid on a moving steel ball bearing given current, number of loops, area of the solenoid for a lab project. I've tried looking through many sources, but was unable to find anything. I also tried looking at this previous discussion...
So i have learned about the ability of Faraday Cage for blocking an external electric field. But is the thickness of the conductor effect the ability? Is there any limit of its thickness so that the cage won't be able to block external electric field anymore? I have read and searched about this...
Hello! I have a question about a GRE problem. It is problem 55 in the attached file. So the answer seems to be (A) but I am a bit confused. Isn't this basically interference, so the right answer would be (C)?
Let's say I have a charge q which is viewed from its rest frame. So it's velocity v is 0. So the so-called magnetic component of its Lorentz force, which is q v x B, is 0. But I can have a magnet moving in this frame of reference.
Let's say the velocity of this magnet according to the charge's...
In Purcell- Electricty and Magnetism book, in the chapter on electromagnetic induction, I found the following explanation regarding the magnetic flux through a circuit of area ##S##.
Consider the circuit in figure, moving in a time ##dt## in a magnetic field ##B##, constant in time (but not...
I have a doubt on this calculation of magnetic field in presence of displacement current. Consider a capacitor of radius ##R## and with plates at distance ##d## being charged: there is a displacement current in it.
Suppose that I want to calculate the magnetic field ##B## at a distance ##r <...
Hey all,
I am working my way through a couple of emag books (Griffiths, Jackson, and Schwinger) and I was wondering if any of y'all have suggestions for problems that you thought were particularly physically insightful or useful.
Cheers,
IR
It has been demonstrated that it is possible to make humans hear sounds using waves.
Abstract From Journal of Applied Physiology
Is there a practical method for shielding? I mean using materials for simple attenuation, and/or altering characteristics of waves (frequency, phase and/or amplitude).
https://postimg.org/image/lg27z8ngn/
1. Homework Statement
in the first one. I need to find the electrical force
in the second one. Lorentz force which exerts the wire on the other element
third. Magnetization (M) for Nickel
quarter. Electromotive force induced on the dipstick
Translate...
Homework Statement
An infinite line of charge with charge density λ is parallel to and a distance d above an infinite grounded conducting plate. What is the charge density σ that is induced in the plate? For simplicity, consider the line of charge to lie along the line x = 0.
Homework...
I'm trying to understand how the various EM tensors work in General Relativity. The only source I've found is https://en.wikipedia.org/wiki/Maxwell%27s_equations_in_curved_spacetime, but there are two things I don't get.
Why do they use ordinary partial derivatives instead of covariant ones...
Homework Statement
Loop of current ##I## sitting in the xy plane. Current goes in counter clockwise direction as seen from positive z axis. Find:
a) the magnetic dipole moment
b) the approximate magnetic field at points far from the origin
c) show that, for points on the z axis, your answer is...
Homework Statement
A long solenoid has a radius of 3 cm, 3000 turn per meter, and carries a current I = IOcos(ωt), where Io is 0.25 A and ω is 628 s−1 . It is placed through a circular loop of wire, radius 5 cm, which has resistance 100 Ω. The magnetic field in a solenoid is B = µonI.
(a) Find...
Hello. I want to study electromagnetism so I can understand it in circuits and for electrical engineering as well.
Are there any good introducotry books? I have done basic mechanics (kinematics motion in a straight line, work, energy, power , ideal pulleys and motion in two dimensions, calculus...
Hello, friends! My textbook, Gettys's Physics, says that the Lorenz gauge choice uses the magnetic vector potential $$\mathbf{A}(\mathbf{x},t):=\frac{\mu_0}{4\pi}\int \frac{\mathbf{J}(\mathbf{y},t-c^{-1}\|\mathbf{x}-\mathbf{y}\|)}{\|\mathbf{x}-\mathbf{y}\|}d^3y $$and the electric potential...
This is not a specific homework problem. It is a lack of understanding in theory relating to a lab report I have to write.
We (my group and I) wrapped a 40 cm PVC pipe in copper wire (very densely and for almost the entire length), applied a current to it, and dropped a permanent magnet...
Homework Statement
Hi everybody! I'm preparing for an exam of electromagnetism, and I am struggling with the last question of this problem (hopefully the two first ones are correctly solved):
Given potential: ##\phi(\vec{r}) = k \frac{q}{r} e^{-r/R}## with ##r=\sqrt{x^2 + y^2 + z^2}## and ##R...
(I'm sorry for my poor English.) In GR the explanation for the bending of light by gravity is that gravity is a curvature in space (and time) and thus light follows the curved space. I was reading about the (undiscovered) graviton. It would have spin 2. Does it mean a graviton would interact...
Electricity flowing through a wire creates it's own magnetic field. So when the electricity is flowing through a wire, it's magnetic field works AGAINST the generator, slowing it down.
So is there is any way to stop slowing down process without increasing amount of current ??
Okay, so we learn in basic physics that electric fields are created by charges and that magnetic fields are created by moving charges. After that, we learn that those two are just two faces of the same coin: the electromagnetic field. Also, we know that electromagnetic waves travel trough the...
Hi!
I am one class away from graduating with a degree in geology from my university. I have a specific interest in geophysics and spent my summer in Ecuador (and spent some time at their Geophysics institute) and in New Mexico working with Los Alamos National Lab using geophysical techniques...
If an insurer were to offer a policy against data loss from a catastrophic event such as an electromagnetic pulse, the insurer would be in no position to pay when the contingency occurs, the reason being that all of his own bank account will have been wiped clean by the same EMP. Therefore I...
So the potential inside a conductor is constant. Does this mean that if there were a conductor, B, inside another conductor, A, the charges of A/B would redistribute such that the electric field inside would be zero (hence constant potential)? This seems logical but a bit too easy?
Also, if it...
I have a confusion regarding Faraday's law of electromagnetism. Consider this diagram
At this instant, the velocity of the rotor is parallel to the field lines, hence, no emf is induced in the rotor. Altetnatively, we can say that the rate of change of flux associated with the rotor is 0 at...
I have to say first that I found quite a similar question under https://www.physicsforums.com/threads/poynting-vector-dilemma.331375/ However those thread ended without real answer.There shall be the following simple setup: A battery, and quite at a distance a light bulb. They are connected by...
So, I'm working with a DC shunt wound motor and I want to calculate the actual voltage production on paper mathematically before building. I have been studying the biot-savart law and understand it to a fair degree. One of my questions is after you get your measurements in Teslas from said law...
hi, nowadays I try to get involved electromagnetic waves equations, and I came across that $$ \nabla $$ is treated like $$ ik $$ and $$ \frac {\partial } {\partial t} $$ is treated like $$ -iw $$ And if you look at the part painted with orange in my attachment, afterwards you can see that $$...
Hi I would like to ask you guys something a little basic but is itching my mind, the question is : do electrons have net movement when dealing with ac currents? Suposing we have a sine wave for voltage and current. Thanks in advance !
PD:please excuse any grammar mistake.
I hope this is right place to post this. I just wanted to get this off of my chest. I am frustrated, and depressed because I am an outsider to the physics community. I am posting this with the hope that somebody else might be able to add perspective to my situation. I apologize if that's...
Hello, I have used Greiner's "Quantum Mechanics: An introduction" and found it to be awesome, bridging the ga between undergraduate and graduate courses.
So, I am thinking of buying some of Greiner's book to use for my other courses and I wanted to ask you what your opinions about the books in...
I need help in calculating the magnetic field outside of an iron core solenoid at different distances.
I have made an electromagnet by taking a 99.99% pure iron (5cm in length and 1 mm in radius) and wrapping wire over it. I have measured it's magnetic field at the end and cannot find an...
hi, I would like to put into words that I really wonder how these lagrangian or lagrangian densities are created. For instance in the link at 59.35 suskind says $$\int A^u dx^u$$ is invariant or action integral. How is this possible ?Could you provide me with the proof?
Homework Statement
We want to calculate the field of a uniformly polarized sphere of radius=R
Homework Equations
V(\vec{r}) = \frac{1}{4 \pi\epsilon_{0}} \oint_{S} \frac{\sigma_{b}}{r} da' + \int_{V} \frac{\rho_{b}}{r} d\tau'
The Attempt at a Solution
i)I know that
\sigma_{b} = P...
So here is my question, and maybe I am not asking it right, but here we go: If electromagnetism prevents me from actually touching anything at a quantum level, how is it that I can get cut by a knife, or get a road rash falling off my bike? If the negative field of electrons that surround...
I was trying to understand how the electric & magnetic forces are related.
I was going through the equations & the simple explanation of relativistic magnetic field given everywhere. Which goes like this...
There is a current carrying conductor & a charge capable of moving outside it. The...
I've been recently trying to understand the concept of paramagnetism, but I feel like I'm running into 2 conflicting models.
Stern–Gerlach seems to suggest that electron spins always point up or down to an incident magnetic field, regardless of their spatial orientation. Similarly, when...
Hi guys, I'm just curious about how does Classical Electrodynamics by Hans Ohanian and Electromagnetic Fields by Ronald Wangsness compare? I know Griffiths is like the way to go when it comes to EM, but personally, I find his book too hand wavy and the explanations are sometimes lacking, so I...
Can anyone please help I want to calculate the power required to make a electromagnet of strength 1 tesla and length 600km.
And how much energy a train consume in traveling per km with speed of 112km/h
Hi
Everyone, I'm trying to justify to myself why
|F(a)| > |F(b)| > |F(c)|
I think I can see why
|F(b)| > |F(c)|
due to special relativity case c observed from
the charges point of view would observe
the charges closer due to lorentz
contraction. As the charge is invariant would
result in...
In special relativity, the electromagnetic field is represented by the tensor
$$F^{\mu\nu} = \begin{pmatrix}0 & -E_{x} & -E_{y} & -E_{z}\\
E_{x} & 0 & -B_{z} & B_{y}\\
E_{y} & B_{z} & 0 & -B_{x}\\
E_{z} & -B_{y} & B_{x} & 0
\end{pmatrix}$$
which is an anti-symmetric matrix. Recalling the...
Homework Statement
The volume between two infinite plates located at x=L and x=-L respectively is filled with a uniform charge density ##\rho##. Calculate the electric field in the regions above, between and below the plates. Calculate the potential difference between the points x=-L and x=L...
Homework Statement
Can someone explain what regenerative breaking is?
Homework Equations
no equations required
The Attempt at a Solution
I understand that this occurs with electric cars. It uses the idea that the electric motor and the electric generator are so similar. But how does the...