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.

Filter by
Sorted by
Tagged with
0
votes
0answers
7 views

Why moving magnet releases more Magnetic radiation as the number of charges near it are increased?

Why does a moving(at constant velocity) magnet release more energy in the form of magnetic fields when the number of charges palced near it are increased? Say two current carrying coils $C1$ and $C2$ ...
0
votes
1answer
31 views

Is it right to say, a static charge (not moving) can't not feel magnetic field?

how far this statement is correct? it takes a moving charge to produce a magnetic field, and it takes another moving electric charge to "feel" it. how far this statement is correct?
1
vote
1answer
17 views

Can electromagnetic field(EMF) meter used to detect electromagnetic pulse(EMP)?

In theory,can electromagnetic field(EMF) meter used to detect electromagnetic pulse(EMP)?
1
vote
1answer
38 views

Electric field in vacuum [closed]

A positive electric charge moves in vacuum and enters a region of space, where there is a uniform electric field, with a velocity perpendicular to the direction of the electric field. What would ...
0
votes
0answers
49 views

What is the lengthscale where electric force and gravity are comparable?

Basically the title. I came across this question while going through old exams. I thought that electromagnetism is stronger than gravity by 40 orders of magnitude more or less, at all scales, so this ...
0
votes
1answer
22 views

What is a constant phase plane?

I have a electromagnetic wave propagating in an arbitrary direction in the space. I do understand that the electric magnetic fields are constant in a plane normal to the direction of propagation. My ...
1
vote
4answers
236 views

Is there a classical explanation of why the electron in the ground state of a hydrogen atom does not spiral into the proton?

R. Feynman was troubled by this question. He claimed there was no classical explanation. In fact by his classical analysis, the electron would spiral into the proton in approximately one nanosecond.
-5
votes
0answers
27 views

we need to obtain equation (5.121) and equation (5.122) with out omitting any step [closed]

these equations should be found accourding to j.d.jackson , classical electrodynamic , 2nd edition
1
vote
2answers
61 views

How show that for a free EM field, the energy of each mode is conserved in time?

For a free electromagnetic field, since different modes do not talk to each other, one would expect that the energy stored in each mode is conserved (or constant) in time. But the energy stored in a ...
0
votes
0answers
11 views

Critical Field outside the Meissner limit - derivation

In Tinkham's "Introduction to Superconductivity" Second Edition, Chapter 2.2.1, the author states that ... the superconducting state becomes energetically unfavorable above the magnetic ...
-2
votes
0answers
40 views

If an iron crystal is fully magnetized spontaneously, estimate the resulting magnetization [closed]

If an iron crystal is fully magnetized spontaneously, estimate the resulting magnetization. I have no idea how to solve this problem. Could anyone help or give any suggestions? I think I need to ...
0
votes
0answers
27 views

Relation of velocities - Electrical and magnetic transformation [closed]

How can next equation be proven by using the transformations about relations between E, B: $$E' = \beta \times B \tag{1}$$ $$ E' = \gamma(E+\beta\times B)\tag{2}$$
0
votes
0answers
16 views

Linearity from fractional equation? (solar cell)

I am doing a little research into solar cells, namely the fill factor. It is a ratio, defined as maximum power divided by theoretical power [of the solar cell]. The maximum power and theoretical power ...
-1
votes
0answers
35 views

Gauss Law: Electrical flux and density of a surface [closed]

Problem: A closed surface with dimensions $a = b = 0.400 m$ and $c = 0.600 m$ is located as in Figure. The left edge of the closed surface is located at position x = a. The electric field throughout ...
0
votes
1answer
79 views

Complex physical quantities

I have a question regarding complex physical quantities. Why do we consider only the real part of a complex physical quantity? Why not the modulus? Since, for $z=a+bi$, we have $|z| = \sqrt{a^2+b^2}$, ...
1
vote
1answer
20 views

A confusing problem in electro- and/or magnetostatics: two parallel cylinders with opposite currents

I got the following problem as a part of my assignment in physics: Equal but opposite currents $J$ flow on the surfaces of two cylinders of radii $R_1$ and $R_2$, respectively, with the axes of the ...
0
votes
0answers
27 views

Magnetostatics in matter ( hollow cylinder with a current through it) [closed]

> An infinite wire carrying current $I$ is placed along the axis of a hollow cylinder of internal and external radii $a$ and $b$ respectively, and of magnetic permissibility $μ$. Write the ...
0
votes
1answer
35 views

Relationship between voltage and distance in electrodynamics

Just to clarify, I’m just now learning about physics for the first time, and ran into some confusion about how voltage works. In electrostatics, I learned that voltage is dependent on distance based ...
0
votes
0answers
55 views

How Lenz's law is based on conservation of energy?

To be honest, I understood Lenz's law. It doesn't violate conservation of energy. Kinetic energy gets coverted to electromotive force (EMF). But why? Like in case of upward thrown ball, kinetic ...
1
vote
0answers
39 views

How is the magnetization $M$ of a material measured?

In a linear material under the influence of an external field $H$, magnetization $M$ is given by \begin{align} {\bf M} = \chi {\bf H}, \end{align} so that the total field inside the material is ${\bf ...
2
votes
1answer
42 views

Why magnetic and electric field obey Helmholtz equation?

I am trying to understand the basic principles of scalar diffraction theory and came across the sentence "E and H obey the Helmholtz equation", what does that mean? Does that mean that each ...
0
votes
0answers
34 views

What is the role of the magnetic moment on wave particle duality

An electron, travelling at high speed relative to an observer, does not radiate unless it undergoes some form of acceleration. Yet we can observe wave like properties under certain measurement ...
0
votes
1answer
28 views

Does induced electric field carry energy just like electrostatic field? [closed]

Does induced electric field carry energy just like electrostatic field?
0
votes
0answers
13 views

Vector identity and Electric Field Screening in Tinkham's

I'm going through Tinkham's "Introduction to Superconductivity" Second Edition. In Chapter 2, the author states that "we obtain \begin{align} -\nabla \times \nabla \times {\bf E} = \...
0
votes
0answers
32 views

The direction of the magnetic field around a conductor

What will be the direction of the magnetic field be around a wire that carries current (straight conductor) between the poles of a permanent magnet? I'm thinking it will be counterclockwise, since ...
61
votes
3answers
6k views

Why don't the Earth's oceans generate a magnetic field?

Many questions have been asked here about why the Earth has a magnetic field, e.g., What is the source of Earth's magnetic field? How does Earth's interior dynamo work? How can an ...
0
votes
1answer
32 views

How does charge flow inside the thickness of parallel plate of a capacitor?

In an uncharged capacitor current enters through one plate, accumulates on its bottom surface (which means positive charges accumulate) and then due to repulsion repels the positive charges on the ...
2
votes
1answer
32 views

Physical interpretation of increasing Reflectivity with increasing $\epsilon_i$ for small $\epsilon_r$

Currently I have plot Reflectivity, $R$ of a generic material (assuming a complex dielectric function, $\epsilon = \epsilon_r + i\epsilon_i$) as a function of $\epsilon_i$ for various $\epsilon_r$ ...
4
votes
4answers
133 views

What is the definition of a magnet or a magnetic field?

Electric forces are the forces which come about between two types of charges, positive and negative. Gravitational forces are the forces between matter. Nuclear forces are the forces which act on the ...
0
votes
1answer
36 views

Does Motional EMF depend on the shape of path taken or depends on the shortest distance between given two points?

A semi-circular conducting wire of radius 2m is rotated in a uniform magnetic field $B=0.1\text{ T}$ ($\vec k$) about point $O$ with angular speed $\omega=10\text{ rad/s}$ as shown in the figure. The ...
0
votes
1answer
34 views

Initial charge in parallel plate capacitor [closed]

Two capacitors $C_1$ and $C_2$ (where $C_1 > C_2$) are charged to the same initial potential difference $\Delta V_i$. The charged capacitors are removed from the battery, and their plates are ...
0
votes
0answers
19 views

Why is the real part of the permittivity the phase angle?

The relative electric permittivity $\epsilon_r$ describes polarization inside a material due to electromagnetic waves (e.g., visible light passing a medium). I understand that the induced dipoles ...
0
votes
0answers
41 views

Angular Acceleration of a wire in a magnetic field [closed]

My physics book presented me with this question: A copper wire with density $D=8960 \;\text{kg}\,\text{m}^{-3}$ is molded in the shape of a circular spire with a radius of $r=0.50\;\text{m}$. The ...
1
vote
0answers
35 views

Equations of Motion for Hidden Photon

I was reading a paper called Parametrically enhanced hidden photon search by Peter Graham et al. In the paper, a Lagrangian that describes the theory of the hidden photon is $$\mathcal{L}=-\frac{1}{4}(...
0
votes
1answer
40 views

Magnetic force vs Electric force on a charged particle

Why is it that a charged particle's speed is constantly changing under the influence of an electric field, but constant when under a magnetic field?
0
votes
1answer
25 views

Hysteresis curve in ferromagnetic materials

Suppose I have a ferromagnetic material that is inside a chamber where you can somehow control the magnetic field. The image represents its magnetization in function of its applied magnetic field. a) ...
1
vote
2answers
68 views

Thomson scattering from Larmor's formula (Jackson's derivation)

The equation numbers below are the same as they appear in Jackson's Classical Electrodynamics. If a plane monochromatic electromagnetic radiation is incident on a free particle of charge $e$ and mass $...
-2
votes
1answer
84 views

What does “Integrating out field” mean?

In Schwartz’s QFT book, there is a couple of exercise problems of particle polarization in chapter 3. I have trouble with finding interaction terms from the given Lagrangians. Is it just okay to ...
1
vote
5answers
131 views

If ${\rm curl} \vec{A} = \vec{0}$, why is $\vec{A}$ a gradient of some function?

I am reading the electrodynamics book by Griffith and am puzzled by a derivation step there. At some point, he shows that ${\rm curl} \vec{A} = \vec{0}$ and then says that since $\vec{A}$ is curl-free,...
0
votes
1answer
31 views

Why is there a little fluctuation when the electricity connects or disconnects?

When the electricity connects (or disconnects), if you look at a light bulb,it would first get on (off), then off (on) and finally get on (off). What is the reason for this? I heard that it is because ...
7
votes
0answers
54 views

Is the magnetic field at the centroid of a closed loop connected at two different points to a battery always zero?

Given a closed 2-dimensional conducting loop, the terminals of a battery are connected at any two points on the loop (but not the same point). As an example, consider a circle of radius $R$; the two ...
0
votes
1answer
18 views

Electric Susceptibility at the Boundary

Section 4.4.2 of Griffiths' Introduction to Electrodynamics has the following footnote: This [the fact that the bound charge density $\rho_b$ is proportional to the free charge density $\rho_f$] does ...
1
vote
0answers
31 views

Reflectivity as a function of complex dielectric function - obtaining negative reflectivity values?

This maybe a bit of a silly question of my part, but I am trying to rewrite the Reflectivity, $R$ as a function of the complex dielectric function $\epsilon = \epsilon_r + i\epsilon_i$. Starting from ...
0
votes
1answer
29 views

Some interpretations of interfering waves

I'm studying propagation of waves. We usually have the most simple cases, when the amplitude, direction of propagation, frequency are equal, but I'm studying some other different cases, that I want to ...
-6
votes
0answers
29 views

physics question [closed]

A copper wire is wrapped 65 times around an unknown core of length $28 \;\text{cm}$. The current in the wire is $800 \;\text{mA}$ and the magnetic field due to the electromagnet is $1.63 \times 10^{-2}...
-1
votes
1answer
72 views

Do magnetic fields really travel with ${}c$ velocity in space?

I was thinking about a situation: In space there is our setup, a wood piece of mass $m$ and a coil and permanent magnet of mass $m$. The coil is placed a light second far from the magnet. The magnet ...
0
votes
0answers
10 views

Complex fourier transformation function [duplicate]

can the FT function can be a complex function ? and if yes what does it mean because in all cases i came across till now the FT function only had a real part
0
votes
2answers
42 views

Why does moving an electrostatically charged object near a compass only attract it temporarily?

I've noticed that if I rub a plastic spoon with some fabric for ~20 seconds and hold it near a compass, it will attract its nearest pole. However, if I keep the spoon stationary, the needle will drift ...
-2
votes
0answers
36 views

I need to know whether these videos are fake or not [closed]

video 1 - https://youtu.be/4CiJKk5kWTo video 2 - https://youtu.be/a0sRo4ew5qA These videos are pretty convincing, but from the physics point of view... idk
0
votes
2answers
75 views

Could we explain how a motor works with special relativity?

At the place where I work there are lots of motors and generators. Could I explain to an apprentice how a motor and/or a generator works with arguments based solely on special relativity?

1
2 3 4 5
303