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.

learn more… | top users | synonyms (5)

0
votes
2answers
50 views

Integrate the law of universal gravitation to get position

I'm trying to write Physics simulation software which simulates gravitational and electric forces between $n$ bodies. I know how constant acceleration is integrated to get distance, but I have no ...
-1
votes
0answers
9 views

Three Charged Particles are at the corners of an equilateral triangle [on hold]

7.00x10^-6 and -4x10^-6 charges. I did this work and it told me I'm off my a multiple of ten but I don't know what I did wrong. E = 9.0x10^9*7.00x10^-6/(0.350m)^2 = 5.14x10^5N/C Ex = ...
2
votes
3answers
68 views

Why would two protons repel?

I understand that two protons would repel due to them both being positively charged, however, wouldn't the strong force act on the two protons pulling them together? Would this mean that in this case ...
2
votes
2answers
36 views

Natural Frequency of an object and the phenomenon of resonance!

I have read about the term natural frequency in quite a lot of places. But I haven't found an explanation as to what is vibrating. It was pretty awkward when I couldn't clearly answer my little sister ...
1
vote
1answer
50 views

Apparent Violation of Energy Conservation in an Electromagnetic system

As shown in the figure a beam of EMW pulse is propagating towards a nearly point charge.Here if we calculate the total energy of the system by the equation mentioned in photo - we get that the total ...
1
vote
1answer
28 views

components of mixed tensor with same indices

If my tensor $a^{\mu\nu}=$ matrix of 4*4 size (let's say, in 1+3 dimensions with mostly negative convention for the metric), what is $a^{\mu}_{\mu}$ ? Is it the trace or the vector of diagonal ...
-2
votes
1answer
37 views

How to convert EM fields to EM waves?

How a body producing electricity and magnetic fields become a body radiating electromagnetic waves?
-2
votes
0answers
16 views

X-rays are absorbed by the atmosphere [on hold]

What happens to x-rays when absorbed in terms of electromagnetic waves?
-1
votes
0answers
17 views

Lorentz force solving and integration [on hold]

I have a question on how to get gyro frequency from lorentz equation. The question is attached below. I have also attached what I have done so far, but looks wrong. How is this question done; a) ...
-5
votes
1answer
17 views

Touch both wires of a 120 Ac power supply [on hold]

ok i have in my house 2 wires the black one and the red one, what could happen y for example I touch both wires with my hand. we have 120 V, Pd. somehow we tried to install a lamp there but didn´t ...
-1
votes
0answers
22 views

what is the relationship between tesla and oersted units?

What is the mathematical relationship between tesla and oersted units? I have a measurement of the upper superconducting critical field Hc2 vs temperature and would like to convert it to oe vs ...
6
votes
2answers
445 views

Why is Xenon favored as the propellant in electric thrusters?

Most of the articles I've read on electric thrusters mention that Xenon is generally, with some exceptions, used as the propellant (or would it be termed reaction mass?). They never mention why ...
0
votes
0answers
34 views

If 2 photons collided head on, what would happen? [duplicate]

If 2 photons, in perfect synch (frequency, amplitude, etc. were all equal) and they collided head on, what would happen? Would they pass right through each other? Would they interfere, then go back to ...
2
votes
2answers
33 views

Magnetic Field and Flow of Vector Potential

I am sorry, when my question is not really concrete, but here we go. Consider the Hamiltonian function $$H(x, \xi) = \frac{1}{2m}\bigl|\xi - eA(x)\bigr|^2$$ corresponding to a charged particle in a ...
0
votes
1answer
44 views

Why does Ampère's force only linearly depend on the distance between the two wires?

When we encountered Ampère's force law our professor stated: In the formula of the magnetic force you don't find $r^2$ as in the gravitational and the electric one because while those directly ...
1
vote
1answer
32 views

Constant magnetic field attenuation by µ-metal (mu-metal)

I am interested in the magnetic field attenuation by µ-metal. Specifically shielding from earth's magnetic field $\boldsymbol{H}_E$ through closed cylindrical layers of such a metal, yielding an ...
0
votes
0answers
12 views

How to infer the wave function $\psi$ of a EM wave?

There was a claim I read somewhere that said the wave function $\psi$ of a EM wave is measurable via $\vec E$ and $\vec H$ Can someone show how this works?
0
votes
1answer
33 views

Is anything without mass an EM wave?

For the longest time I thought the distinction between matter wave and other types of wave is the non-relativist mass of the "thing" under discussion. Photons are EM wave, electrons are matter waves. ...
0
votes
0answers
25 views

Does the non electrostatic force moves charges in open circuit?

I would like to ask you a question i have about the non electrostatic force inside a emf device in open circuit situation. The following text is a text from Univeristy Physics ( Young and Freedman pg ...
-1
votes
2answers
51 views

Traveling to Mars in 24 Days

I am trying to calculate an electromagnetic rail launch from the Moon but I need to know if humans can survive the launch. Please see the specs below. 150 miles of track Proposed final launch speed ...
0
votes
1answer
35 views

Magnetic Wire Doesn't conduct Electricity

I recently bought a 22 and 30 gauge loop of magnetic wire from radio-shack. The loops of wire were colored differently (if this makes any difference) and on the package it noted how these wires were ...
1
vote
0answers
21 views

Frame dependence

I was reading an article about magnetospheres, and came across this quote: This supersonic ionized gas, or plasma, called the solar wind carries with it a magnetic field and a frame dependent ...
0
votes
0answers
28 views

can magnet used in engines

My friend has told an idea that if the same poled magnets are placed in the motors instead of engines,it will produce the ultimate energy.because same poles are repelling each other. is it possible?
0
votes
1answer
36 views

Why direction of Ampere's Law follows right hand rule? [duplicate]

Why direction of Ampere's Law follows right hand rule?
2
votes
1answer
42 views

Why does larger permittivity of a medium cause light to propagate slower?

I was wondering about what physically happens when light is transmitted through a non-magnetic medium. Specifically, I’m trying to visualize how materials slow down light as the electromagnetic wave ...
3
votes
1answer
52 views

Why does choosing a time break covariance?

I'm reading that in EM theory, in hamiltonian formalism, we choose a specific reference frame with a specific time, and that this breaks covariance. Why? Surely it's simple because it's just stated ...
1
vote
1answer
39 views

Spherical Magnet Inside a Solenoid

When passing a bar magnet through a long solenoid why is it that the induced emf when the magnet is in the middle of the solenoid is zero? And if a spherical magnet is put inside the solenoid, will ...
0
votes
0answers
20 views

Electric dipolar moment of a half wave antenna

We have an antenna ($\lambda = L/2$), of length $L$ with a current density: $$\vec j=I\sin [k(|z|-L/2)]\delta(x)\delta(y)e^{-i\omega t}\hat e_z$$ I want to calculate its electric dipole moment. I ...
1
vote
0answers
22 views

Interaction between charged particles through static electric fields [duplicate]

I generally find it pretty primitive to accept that static charges communicate with the help of static electric fields without any exchange going on between them such as electromagnetic waves. I ...
0
votes
0answers
16 views

form of manganese with highest magnetic permeability

what form of manganese -- metal, MnO, Mn3O4, or any ionic compound, has the highest magnetic permeability? i'm using this as a magnetic core for inductors. yes, there are better materials if i want ...
0
votes
0answers
31 views

A transverse sinusoidal wave [closed]

A transverse sinusoidal wave on a string has a period T = 41.0 ms and travels in the negative x direction with a speed of 30.0 m/s. At t = 0, a particle on the string at x = 0 has a transverse ...
0
votes
3answers
54 views

What is the physical significance of the negative amplitude of a light wave?

I want to understand what is the physical significance of negative amplitude of a light wave? In an ac electrical circuit, I understand that negative amplitude signifies the amplitude measured when ...
0
votes
1answer
16 views

Larmor precession for time-changing magnetic field?

Wikipedia gives the formula for Larmor precession for the magnetic moment in an external field ${\mathbf B}$. But nothing at all is mentioned about whether the field can have a time dependence. Since ...
0
votes
0answers
15 views

paramagnets with high magnetic susceptibility

i'm thinking of using paramagnets as cores for receiving antennas, same as ferrite rods are used as the core for AM radio antennas. why paramagnets? a material that can demagnetize itself after being ...
1
vote
4answers
95 views

Why does a magnetic field go anticlockwise of the direction of current?

Why never clockwise? How does it 'know' to go anticlockwise?
-2
votes
0answers
16 views

Did Insulators are antistatic materials? [closed]

I like to know the all the insulating materials are antistatic materials.
0
votes
3answers
54 views

Does a moving magnetic field produce an electric field?

Consider a conducting rod of length $L$ moving with speed $v$ in a magnetic field of intensity $B$. Let all the three parameters be perpendicular to each other. Moving charges in a magnetic field ...
0
votes
0answers
16 views

Charge movement in a rotating EM field (relativistic)

I have this problem let's see if anyone can help me advance a little. (No need to say that if my approach is ridiculous or too hard and anyone knows a better solution, I would like to know it). I ...
1
vote
1answer
46 views

Why do electron and hole mobilities decrease with temperature?

From page 35 of "Microelectronics" by Millman Grabel Mobility $\mu$ decreases with temperature because more carriers are present and these carriers are more energetic at higher temperatures. ...
1
vote
1answer
50 views

electron-gas theory of a metal (drude model) - intuition

I'm back to studying "Microelectronics" by Millman & Grabel (2nd ed.). The book makes some references to the electron-gas theory, and I found out to have some problems with my intuition. At each ...
4
votes
2answers
61 views

How to get the electric field strength of a plate as approximation of a sphere

Suppose you know that the electric field in distance $r > R$ from the center of a charged sphere with charge $Q$ and radius $R$ is given by: $$ E = \frac{1}{4\pi\epsilon_0} \frac{Q}{r^2} $$ ...
3
votes
1answer
123 views

Why is there no force between a current loop and an open loop

This is a question about figure 2 in this article. Why there will be no force between the wires despite of having a relative velocity between electrons in the two wires?
7
votes
1answer
144 views

What is the quantum state of a static electric field?

This is something that I've been curious about for some time. A coherent, monochromatic electromagnetic wave is well described by a coherent state $|\alpha\rangle$. The quantum treatment of the ...
-2
votes
0answers
26 views

Vector Potential and electric field [closed]

The components of a vector potential $A_\mu= (A_0,A_1,A_2,A_3)$ are given by $$A_\mu= k(-xyz,yzt,zxt,xyt)$$ where k is a constant. What are the three components of the electric ...
1
vote
0answers
38 views

Can photons travel through space independent of time?

I read an article about advanced photons and they stated that photons traveled back in time to hit an electron. Can photons really travel back in time and if so, how?
-2
votes
1answer
18 views

Transmission line given SWR and Wave Lenght, calculate Reflexion Coeficient [closed]

Given a transmision line with SWR = 7, we know in Wave_length/4 there is a maximun of the stationary wave. What is the reflexion coefficient in z=0¿? I also have another example with SWR = 7 too and ...
0
votes
0answers
34 views

To What Extent are Magnetism and Gravity Related and Unrelated? [duplicate]

I find many people (especially UFO-ologists) are quick to say there is an interplay between magnetism and gravity, especially when explaining antigravity of UFOs. On the other side, I see those who ...
1
vote
2answers
52 views

Magnetic Field of a Current Loop using Ampère's Law

A typical exercise while introducing the Biot-Savart Law is to calculate the magnetic field caused by a circular current loop at a point P located in its central axis, as shown in the following ...
3
votes
1answer
145 views

Need of small charge in definition of electric field?

Why do we need infinitesimally small charge in definition of electric field? Since the test charge cannot exert force on itself, F on test charge will not change whatever the value of test charge q ...
1
vote
0answers
35 views

Concrete example of Earnshaw's Theorem

I'm struggling to understand Earnshaw's Theorem. I've tried reading the original paper, and the wikipedia article. I know enough math to be able to understand the mathematics of the theorem, but I ...