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 (6)

4
votes
1answer
110 views

Why didn't Newton study electricity and magnetism?

This is a soft question about the history of physics. In Newton's time, electrical and magnetic phenomena (such as amber attracting things or the alignment of compass needles) were well known. Yet I ...
0
votes
0answers
36 views

How inversion layer shields electric field?

This question is somewhat relating to electronics but I think it fits better with physics. The leccture here (slide 13) shows that the gate to body capacitance (Cgb) in linear region is 0. However, ...
0
votes
1answer
44 views

Find the current enclosed in the loop

Magnetic field at point $(x,y,z)$ is given by $\overrightarrow B = \dfrac{B_0y}{\sqrt{ x^2+y^2}}\hat i - \dfrac{B_0x}{\sqrt{ x^2+y^2}}\hat j $. Find current enclosed in the loop $x^2+y^2=r^2$. My ...
1
vote
1answer
11 views

Magnetizing a ferromagnetic material.

if i pass a DC current directly through iron or steel or something ferromagnetic, Would that magnetize that material? And would it be magnetized permanently? Another question, does anyone know what ...
1
vote
1answer
51 views

Name of electric force

during a lab experiment, i noticed that a metal ball has a much harder time rolling on metal rails when their is a current passing through it and the rails. I was wondering why and if there was a name ...
0
votes
0answers
25 views

Electro-magnetic fields and Faraday Cages

If you have an area that is affected by an electromagnetic field, would it be possible to build a Faraday cage and then build a device INSIDE the Faraday cage so that it would work (as opposed to ...
0
votes
0answers
30 views

Domains in Ferromagnetism

I am currently reading the book "Introduction to electrodynamics" by David J. Griffiths. As far as I understood, a Ferromagnet when not applying external magnetic field, the magnetic dipoles inside a ...
2
votes
1answer
67 views

Need clarity about relativity/magnetism explanation

Please bear with me - this is not a duplicate question.... From what limited knowledge I have gathered, it seems that when two wires in parallel are carrying equal current, the electrons moving in ...
-4
votes
1answer
25 views

Could an infinite spinning windmill create endless electricity? [closed]

This is not so much a question about if this idea is physically possibly, but more a question of if it was possible. If a magnet could somehow push a windmill around at a constant speed continuously, ...
1
vote
1answer
38 views

Refractive index of plasma dependance on temperature

How does the refractive index of plasma changes with temperature? Temperature is not high enough for new ionization. Would it be like in gas p/T dependence ? http://farside.ph.utexas.edu/teaching/em/...
0
votes
0answers
26 views

What is the difference between the Lorentz force in a cloud chamber and the repelling/attracting force between magnets?

In a cloud chamber charged particles are bend by a magnetic field where the Lorentz force is causing the bending. But when a ferromagnetic material is attracted or repelled by a magnet it is more or ...
1
vote
0answers
42 views

What started the magnetic field of Earth [duplicate]

The Dynamo theory gives a good explanation of the magnetic field of the Earth: the Coriolis force focus inner currents into current spirals generating magnetic(s) field(s). What I'm trying to ...
1
vote
1answer
63 views

Differential equation in RL-circuit

I am self-studying electromagnetism right now (by reading University Physics 13th edition) and for some reason I always want to understand things in a crystalclear way and in depth. Now look at this ...
3
votes
1answer
61 views

Can Light Waves Be Irregular?

From what I understand, electromagnetic radiation produced by an antenna is of the frequency that corresponds to the motion of the electrons moving around in the antenna. And I assume that the ...
3
votes
1answer
77 views

Can Non-Magnetic Dust Particles become magnetic if their particle size is decreased (by grinding them probably)?

Problem: Take some dust particles whose size is big. Bring a magnet near them. They do not get attracted to the magnet and thus we conclude that they are non-magnetic. However, when you grind the ...
1
vote
1answer
35 views

Is energy required to preserve information on a disk?

I was just wondering if the large files I have on my PC, which have remained there for years, take up some energy to remain preserved. Just curious. Maybe a silly question after all, but I would like ...
0
votes
0answers
23 views

What is magnetic levitation? Can it be done with electromagnets?

I have done a bit of a research on magnetic levitation and maglev trains but I fail to understand the phenomena. I also saw some videos on YouTube , they were about superconductors and magnets. I ...
0
votes
0answers
13 views

Create spinning / modulating plasma effect without spinning the whole appartus

I'm trying to create a variable spinning / modulating plasma effect without turning the whole apparatus as seen in the video. https://www.youtube.com/watch?v=Wis_HEa3X84 Is it possible to just use ...
2
votes
0answers
40 views

Electromagnetic field transformations under rotations

If you have magnetization vector in vertical magnetic field, it starts precessing. If you do a transformation to rotating coordinate system you obtain a stationary magnetization. Is there a direct ...
3
votes
1answer
110 views

How to evaluate possible values of spin of two photon system?

Photon hasn't well defined quantity such as spin. Instead of it, it is characterized by helicity $h$. Let's assume state of two photons in CM frame (with $\mathbf k$ being the momentum of one of ...
1
vote
0answers
40 views

Charged pendulum oscillations

Recently, a question was asked in our school, regarding the calculation of the time period of a charged pendulum bob suspended in an electric field with the help of an insulating thread(gravity also ...
3
votes
0answers
81 views

Question on the Derivation of Lorentz Invariance of Electric Charge

On Zwiebach's "A First Course in String Theory" textbook, there is a problem 8.2 that derives the invariance of electric charge given a few assumptions: 1. Conservation of Maxwell 4-current $j = (c\...
0
votes
2answers
59 views

If photons mediate EM force? How can they tell to be attracting? [duplicate]

Like a photon is neutral, when a proton say feels a push from another proton, how does the proton know it was a proton pushing it and not an electron pulling it? Im not asking how the details work of ...
1
vote
3answers
47 views

Charged Particles: How is energy conserved?

I can seem to understand where the energy comes from when two particles accelerate. I tried searching through the forums and it seems like the answer is always potential energy was the source of ...
0
votes
0answers
25 views

Resistance increase with length because of more scattering?

I am referring to one of the answers to this old question. I can't add comment to it because I don't have enough reputation. So here I rephrase the question: does resistance increase with length ...
3
votes
1answer
160 views

Is Biot-Savart Law valid for time-varying currents unlike Ampere's law?

I have just finished learning the basics of magnetism, and it should be noted that I am not very familiar with Maxwell's equations. Note: In the question, when I say "Ampere's Law", I am referring ...
2
votes
0answers
66 views

Confusion in reaction force of Ampere's Force Law [closed]

I am reading Maxwell's "A Treatise on Electricity and Magnetism" and I have some confusion in the following pages: The element ds is resolved into its components $\alpha$ and $\beta$;and the ...
1
vote
2answers
45 views

Is the energy needed for a current through a straight and a coiled wire different?

When you add current to a straight piece of wire does it use less electricity than if it was coiled? Does the curve of the wire and proximity to itself make a difference in energy consumption?
1
vote
2answers
86 views

Why the reflection of randomly-polarized light is not random? [closed]

"Reflected light is polarized". The following photo demonstrates this: (source) When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore ...
2
votes
1answer
66 views

Clarifications on Ampere's Law [closed]

I have just learnt Ampere's Law, useful for calculating the magnetic field in situations having a high degree of symmetry. However, I have some conceptual doubts regarding it: Before I begin, I would ...
0
votes
2answers
74 views

Why is the magnetic force not (never) in the opposite direction

In this question I'm talking about the left-handed orientation for the direction of the $x$, $y$ and $z$-axis. This is the coordinate system at the left of the picture below. I learnt that when you ...
1
vote
1answer
63 views

Can we derive Biot Savart law from Coulomb's law?

Can we derive Biot Savart law from Coulomb's law by setting a current source at an instant in place of one of the charges? Let's say $dl$ is the length of the conductor having $dQ$ charge which ...
-3
votes
0answers
51 views

Why does the Microwave disturb the Internet Signal?

I have no back round in physics but was wondering how come every time the microwave is turned on, the internet slows down dramatically?
3
votes
1answer
47 views

A puzzler in induction and special relativity

Some reading I was doing jogged my memory about a puzzle in E&M that hit me back in my undergrad days, but I just let it go at the time and never found an answer. A pretty common undergrad E&...
0
votes
2answers
51 views

What is a magnetic line of force? [closed]

Do magnetic limes of force 'flow'? If so, what is it that is flowing? What is the 'line of force' composed of?
3
votes
0answers
44 views

Lagrangian of classical electromagnetism without $A_{\mu}$ field [duplicate]

Is there a Lagrangian reproducing Maxwell's equations without the use of the scalar and vector potential? Obviously $\mathcal{L} = -\frac14F_{\mu \nu}F^{\mu \nu}$ doesn't work since in terms of $E$ ...
0
votes
1answer
36 views

How can a sinusoid be a steady current? [duplicate]

As far as I understand it, a steady/stationary/constant current is defined to have $dJ/dt=0$ (i.e., no explicit time dependence). So I would say that sinusoids cannot produce steady currents, yet ...
0
votes
0answers
45 views

What one would observe on extremely high voltages?

I am interested which physical processes generate the highest electrical voltage and what the highest measured voltage is. In everyday life, electrostatic charges e.g. while walking with socks on a ...
0
votes
0answers
27 views

Newton's third law, weak and strong law of action and reaction [duplicate]

In the case of a system of moving charges forces between charges is obtained by Biot-Savart law. But it violates both action and reaction law. How can we prove that?
0
votes
1answer
36 views

Laser as an optical oscillator

How can Laser can be compared to a positive feedback amplifier? Does the two conditions for oscillator holds good for lasers too.
0
votes
1answer
87 views

How to find the magnetic field due to a revolving electron of hydrogen atom in first orbit

So, I was thinking about the Bohr model of atom and I started to wonder how we could find the magnetic field due to a revolving electron (produced at the location of proton) of hydrogen atom in first ...
0
votes
0answers
23 views

Circuit with capacitor and battery- why same voltage?

If we connect a capacitor and a battery in the same circuit, what makes the charge move until the voltage on the capacitor is the same as voltage on battery?
30
votes
4answers
4k views

What is momentum really?

Wikipedia defines momentum as in classical mechanics: In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object. However, an ...
0
votes
1answer
45 views

Intuition differential ampere's law

Ampere's differential law states that - $$\nabla \times {\bf B} = \frac{4 \pi \, {\bf J}}{c}$$ I know to derive amperes integral form from special relativity, and to use stokes theorem in order to ...
2
votes
0answers
41 views

Consistency of atomic magnetic dipole spatial orientation with Stern-Gerlach picture of electrons

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 ...
2
votes
1answer
35 views

How to properly apply Ampere's Law in this case?(Square Loop)

Suppose ABCD is square loop (conducting). There is a wire carrying a current $I$ into the plane of paper within the region of loop. So how to properly apply Ampere's Law in this case? The closed ...
0
votes
0answers
51 views

Does gravitational radiation have a formalism similar to Wheeler-Feynman electrodynamics?

Binary systems radiate energy away in gravitational waves as the orbits of the two masses spiral in towards each other. My understanding of gravity is that we think of it as a mediator of particle-...
0
votes
0answers
27 views

What difference does it make if the turns in a tesla coil overlap?

Would a tesla coil in which the primary coil is made by overlapping the turns of the wire work?
1
vote
1answer
60 views

Electricial impedance - why does it work?

I learn electricity from Purcell's book. Analyzing AC circuits is easier with complex numbers. I understand you have to replace the regular representations with those containing complex numbers ...
0
votes
1answer
37 views

main cause of self charging of unshorted capacitors?

In the lab, we keep all of the high voltage capacitors shorted when not in use, and rightfully so. They tend to spontaneously charge when left for some time and become extremely dangerous. while the ...