Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [electromagnetism]

The classical theory of electric and magnetic fields, both in the static and dynamic case. Also covers general questions about magnets, electric attraction/repulsion etc. Distinct from electrical-engineering.

-1
votes
0answers
9 views

Capacitance of coplanar capacitor

I wanted to calculate the capacitance of capacitor with coplanar plates. How to do that? The dimensions of plate are width w, length l and the gap between plates is a.
0
votes
1answer
10 views

How to contain air ions inside a chamber without loosing their charge?

I would like to create an experiment where I would hold ionized air molecules. Most likely negative O2-1 ions. I am looking for the most appropriate enclosure so that the ions do lose as little of ...
0
votes
1answer
18 views

Calculating refractionindex of water given permittivity

I'm a bit confused. The refraction index is calculated by $$n=\frac{c}{v},\tag1$$ where $c$ is the lightspeed and $v$ is the phasevelocity of light in the medium of interest, water in this case. In ...
0
votes
0answers
16 views

Different prediction about the motion of a charge as observed by two different observers?

Suppose a charge is at rest in the laboratory frame. Also say two observers in two vehicles A and B are approaching towards it. Let A is accelerating towards it and B is moving uniformly towards it. ...
-1
votes
0answers
13 views

Repost: TORQUE GIVEN BY MAGNETIC FIELD [duplicate]

The magnetic torque acting on a loop of magnetic moment M placed in a magnetic field B, is given by τ=M×B. My question is, about which axis does this give the torque about? Is it the instantaneous ...
0
votes
0answers
23 views

Transformer Equation Confusion

I have read some posts on here which I think to revolve around my problem too but couldn't really understand the explanations. So basically, I have seen how the Transformer equation is derived: $\...
0
votes
1answer
30 views

Confusion regarding torque given by M×B

The magnetic torque acting on a loop of magnetic moment M placed in a magnetic field B, is given by τ=M×B. My question is, about which axis does this give the torque about? Is it the instantaneous ...
0
votes
0answers
16 views

Magnetic permeability and susceptibility

I read about relative permeability and susceptibility but didn't get those. I imagined four different conditions a current carrying solenoid is kept in air it is transferred to water a ferromagnetic ...
0
votes
1answer
12 views

Magnetic field of tilted toroidal coil

Lets think about a toroidal coil. We can think that toroidal coil is set of circles. The external magnetic field of coil is zero. Then what if we tilt these circles in same direction? Is external mag ...
1
vote
1answer
23 views

Direction of magnetic field around a straight current carrying wire

I am currently studying for O Level and I have been learning about electromagnetism for the past year. The topic has never clicked for me because I've never been taught the true relationship between ...
3
votes
2answers
66 views

The Meaning of Electromagnetic 'News' in Griffiths Book

In the Introduction to Electrodynamics book, by David J. Griffiths, 4th edition, page 60, the author makes the following statement: "it is not the position, velocity, and acceleration of Q right now ...
2
votes
1answer
54 views

EMF generated by a rotating rod can be zero?

I have taken a look at this question: Emf generated by a rotating rod But my question is different: A metallic rod is being rotated in a uniform magnetic field with a constant angular velocity $\...
0
votes
0answers
12 views

Electric field of a line of Charge on it axis using electric potential

We have a line of charge with length $L$ and charge density $\lambda$ and we want to find its Electric field on a point $p$ with distance $d$ from one end of it using potential. I drew a picture like ...
0
votes
2answers
29 views

Could a solid object made entirely of antimatter safely “touch” ordinary matter without annihilating each other because of EM force?

Most is said about the anti-particles annihilating their ordinary particles counterparts. When antimatter forms anti-atoms, it is said they behave like ordinary matter. Since atoms are more stable ...
2
votes
1answer
33 views

How is it possible that one face of my electromagnet produces stronger magnetic field than the other?

I made an electromagnet in my lab by having the machine shop cut through a toroid core and hand-winding wire around it. The objective is to have a region of uniform magnetic field above the gap for ...
2
votes
2answers
43 views

Railgun design, which is preferred, voltage or farads?

I am building a rail gun for a physics project, but I am confused on whether to use capacitors like 2.7V 500F capacitors or a 400V 3300uF capacitor. Most tutorials seem to use many 400V ones in ...
0
votes
2answers
38 views

Magnetic field of long cylindrical wire

i have been studying electromagnetism on my own and I got a question about an exercise in David Griffiths, Introduction to Electrodynamics book. So I'm asked to calculate the magnetic field both ...
0
votes
1answer
39 views

Is this physics youtube video misleading? (Motional EMF)

I apologize that this is a not a normal post (i.e. not using MathJax but instead posting a video). https://youtu.be/Wgtw5lPKFXI?t=401 In this video (timestamped properly) the physics teacher claims ...
0
votes
0answers
11 views

Simple Electric Motor Didn't Working [on hold]

So I'm making a simple electric motor using 9V battery as power source for my final project. The problem is my motor wont spinning at all. I've scrapped both sides to exposed the wire but it still ...
0
votes
1answer
22 views

EM- waves in anisotropic medium

When ElectroMagnetic waves from vacuum enter the anisotropic medium. If the $\epsilon$(permittivity) matrix is diagonal (with not all diagonal entries being equal). There'll be two waves in the ...
0
votes
0answers
30 views

Proper utilization of Ampere’s Law

I am tasked with finding the magnetic field due to a bus bar, which seems to have the exact same set up as Problem 7.62 in the fourth edition of Griffiths' textbook on Electrodynamics. To which I ...
1
vote
0answers
14 views

Electron accelerated by gravity and electromagnetic radiation [duplicate]

If electron (or other charged particle) is accelerated by gravity (a very weak force), it should emit electromagnetic radiation. Is there any experimental evidence that gravity does indeed cause such ...
-2
votes
0answers
19 views

Doubt regarding surface density of Dielectrics

How the surface density of a dielectric is given by the dot product of normal vector and polarization vector?
0
votes
1answer
61 views

What is the physical interpretation of the derivative of a particle field?

I am learning quantum field theory, specifically the quantization of the electromagnetic field. We have this Laplacian $$ \mathcal{L} = -\frac{1}{2} \partial_\mu A_\nu \partial^\mu A^\nu -j_\mu A^\mu $...
0
votes
1answer
44 views

Integral version of Ampere's law: who doesn't current outside the surface contribute to $\oint B\cdot d\ell$?

I have a question about why this is true $\oint B\cdot d\ell = \mu_0$ $I_{enclosed}$ My problem is that im not really seeing visually or mathematically why the magnetic field generated by a current ...
0
votes
0answers
10 views

What is the gravitational torque on a square frame?

A rigid wire is in the shape of a square of edge-lenth L, mass m and it carries a current I. The square lies on a flat horizontal surface, with a magnetic field of magnitude B is parallel to two edges ...
0
votes
0answers
7 views

how is motion possible between a magnet and a superconductor

from my understanding of relative motion between a magnet and a conductor is that eddy currents work to oppose said motion but cannot entirely because of losses in the form of resistance, but without ...
0
votes
1answer
25 views

Vacuum to hold object [on hold]

Can a 3-6V small motor create enough vacuum to lift and hold a porous object the size of an extra stength tylenol or peanut M&M? I am not an academic, but would appreciate any thoughts or advice.
3
votes
1answer
52 views

Explain why the magnets move towards eachother in this setup

I have two bar magnets (actually stacks of small magnets, but I believe they should behave the same) attached to a stack of (presumably conductive) coins, and not diametrically opposite. When I ...
0
votes
0answers
31 views

A (probably silly) doubt regarding motion of bar magnet

So my instructor was teaching electrodynamics the other day, and he analysed the electric and magnetic field of the bar magnet moving with velocity v in x direction, first from the ground frame and ...
1
vote
1answer
42 views

Is the Electric and Magnetic field in an EM wave interacting in the same way static E and B fields?

Sorry by the title, I don't know how to ask this: What happens to a charge when some EM wave passes across it? If we have an EM wave with really low frequency, is this basically the same as having a ...
0
votes
0answers
23 views

Nature of interaction of two magnetic dipoles

Is the force of interaction between two magnetic dipoles a conservative force? If not, how do we find that force?
4
votes
1answer
53 views

Would a superconductor act similarly to copper when braking a strong magnet on a pendulum

I recently watched this gif from this video, showing a magnet swinging towards a large disk of copper, where it stops gently before hitting the magnet. I understand that the eddy currents have a ...
0
votes
0answers
16 views

Observing charge from non inertial frame

Charge radiates EMW when accelerated. But what if we are in non inertial frame and observe charge. Does it still emit EMW. (Another question: do we observe the magnetic effects of a rest charge if we ...
0
votes
2answers
63 views

What is meant by “changing magnetic field”

At first I thought it was the consequence of an object moving from an area of high to low or low to high flux density, but that doesn’t help understand what is meant by “a changing magnetic field” ...
1
vote
2answers
45 views

How can there be a voltage across an inductor if the voltage through any conductor is zero?

It's commonly taught that the electric field in a conductive material is zero. Hence the voltage through a perfectly conductive material is zero. I however when learning about inductors in physics ...
0
votes
0answers
20 views

Simulating torque between axially magnetized cylinders

Consider the following system of cylinders with axial magnetization (shown in red): Let cylinder 1 be the top cylinder and cylinder 2 the bottom one. The origin of the system is placed at the point ...
1
vote
1answer
56 views

Analytic Solutions to Magnetic Fields of Circular Current Loop

I came across an interesting problem and am wondering if there is a quick answer to it from someone who's done this before before I whip out the books of integral tables. Analytic expressions from ...
0
votes
1answer
53 views

Lorentz transformations: Distance vs “retarded distance”

Suppose I have a charge situated at rest in one inertial coordinate system. The field of that drops inversely with the square of the distance. If I perform a Lorentz boost where $$v^2« c^2$$ (not ...
2
votes
0answers
46 views

Visualizing EM fields

Personally, I have trouble visualizing a flock of birds without the birds. I have the same trouble trying to visualize an EM field without the photons. More than once, I have been hounded off of the ...
0
votes
1answer
28 views

Why does the voltage across resistor R decrease as we close the circuit?

I understand why there should be an increase in voltage across a capacitor during the charging process of it and why there should be a decrease in current I during that process. What I don't ...
0
votes
2answers
41 views

Why, precisely, do three elements in a row (iron, cobalt, nickel) show ferromagnetism, but not the elements below them on the table?

The same is true for Neodymium, Promethium and Samarium, right? But like the first three, they are consecutive, not above and below each other. Somehow only elements in those two ferromagnetic 'hot-...
0
votes
0answers
10 views

Why does mode is confined to higher index material in the waveguide cross section?

I know the EM mode is confined to higher index material and its result can easily be seen after calculating the eigenmode within the cross-section of the waveguide. But having trouble to understand ...
1
vote
1answer
42 views

Magnesium has no unpaired electrons then why is it paramagnetic?

Paramagnetism is often associated with presence of unpaired electrons in atomic orbitals of atoms of the element.But magnesium has no unpaired electrons in it's atomic orbitals but still is ...
0
votes
1answer
41 views

Infinite Electricity from Photon Inside Closed Box with Magnet Attached in a Coil? (Thought-experiment)

Let's say I have a very large box with a magnet attached to the outside. Inside the box there is a perfect mirror on each side. I open my box and quickly shoot in one photon before shutting it. After ...
0
votes
0answers
23 views

Is there a motor design where a rotor gradually moves into a stater? [on hold]

I was wondering if there is a motor/generator design where the rotor moves gradually in and out of the stator along the axis of rotation, or the stator over the rotor, but the primary motion is rotary,...
0
votes
0answers
13 views

How to calculate the magnetic field at a fixed point due to a moving solenoid and a variable current?

I understand that we can use the Biot-Savart law to determine the magnetic field at a single point given a single current. However, if the source of the magnetic field (say, a solenoid) was physically ...
0
votes
0answers
26 views

Magnetic energy due to a line current

I am trying find the magnetic energy due to a straight line current at the centre of a cylindrical container of radius $R$. If I use the formula $$ U_{B}=\frac{1}{2\mu_0}\int_{V} B^2 d{\tau} $$ in the ...
0
votes
0answers
25 views

An example regarding Faraday's and Lenz's Law

Consider the following configuration : Where we have a closed loop near a current carrying wire with the given direction. If we need to calculate the induced emf which results because of moving the ...
2
votes
2answers
83 views

How Maxwell theory of electromagnetism solved action at a distance problem?

According to wikipedia Maxwell's equations were an essential inspiration for Einstein's development of special relativity. Possibly the most important aspect was their denial of instantaneous action ...