Questions tagged [electromagnetism]

The kind of magic without which all of this wouldn't be possible. This tag should be used for questions about the **physics** of the fields that charged particles create and how these fields interact. It should not be used for all questions involving electromagnetism, that would be everything on the site.

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34 views

How strong should a magnet be to detach the magnetic locks?

I know that security tags can be removed by using the magnets. But how can I determine the strength of these magnets that can detach the tags? And does the same strength be applicable to ...
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Inductor dimensions as a function of time(?)

While perusing the text book "Foundations of Analog and Digital Electronic Circuits" by Anant Agarwal , I came across this text in the section on inductors: Why are the dimensions of the ...
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How does the gap between coils and magnets affect BLDCs

I just came across the doubt about how the space between the stator and the rotor in Brushless DC motors affect their performance. Of course the further apart coils and magnets are, the least torque ...
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Capacitance of 2 angled conducting plates

I have to determine the capacitance of 2 conducting plate (fringe fields are ignored) with a certain area (5m^2 here) with a gap separating them (4mm here). The second plate is inclined at an angle of ...
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EMP Halbach Array

Let's say I have a horizontal facing halbach array with equal north and south poles aligned one after the other, and a large circular gap in between them. If I fire an EMP gun through it, wouldn't the ...
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Please help me solve this electromagnetics problem

A non uniform surface charge density of 5p/(p^2+1) nC/m^2 lies in the plane z=2m whereever p<5m; ps = 0 for p>5m. How much electric flux leaves the circular region p<5m, z=2m.
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Construction for a homogeneous field using permanent magnets

Please let me describe what I am trying to achieve and I will pose my question in the end. I am trying to design a small chamber which can have a uniform magnetic field inside. I want to see if a ...
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Bi polar pulse magnetizer controlled by arduino

Hello, I am trying to make a bipolar pulse magnetiser based on the pulse magnetizer design on instructables. I attached my circuit design as image. g1 and g2 terminals of the thyristors will be ...
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Magnetic vector potential and displacement current

I'm reviewing some EM theory and I've come across something that doesn't make sense to me. My textbook states that the magnetic vector potential is defined such that \$ \textbf{B}=\nabla\times\textbf{...
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Importance of Sine Waves And Maxwell's Equations

Sine waves, by a huge margin, are the most important waveform in electronics - we measure a circuit's frequency response with sine waves and represent all other signals through sine waves, with the ...
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What are non-reciprocal bandpass filters?

I am not an electrical engineer. I have come to know about a term called as "Non-reciprocal Bandpass filters" which seems to be useful to me. Here are some links to the papers (unfortunately ...
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Why do ICs interconnects have squared corners

I was wondering, why do ICs interconnects have squared corners if they carry hi-frequency signals? (considering most transmission lines that handle high speed signals have chamfered/beveled corners ...
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Series RLC circuit [duplicate]

Suppose a series RLC circuit has its resonance frequency f_r. If we apply AC current of frequency f_r to this series RLC circuit then circuit has maximum current as output. My question is little bit ...
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Why don't stepper motors ring indefinitely?

I don't have much of a EM background but I have used stepper motors for things. What's not clear to me is why don't stepper motors ring indefinitely? Excluding physical friction, what actually causes ...
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How do we choose refractive index value in optical fiber design?

It is known that, given two media with refractive indeces \$n_1\$ and \$n_2 < n_1\$, if rays come from medium 1 they will be totally reflected if their angle of incidence is higher than the ...
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4answers
729 views

What would happen to the magnetic fields of a solenoid if it were wrapped around a hollow ferromagnetic core?

I'm well aware that a solenoid wrapped around a solid ferromagnetic core produces a stronger magnetic field, but what about a hollow ferromagnetic core? Would the fields farther from the center near ...
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Obtain magnetic field strength (H) of a condenser [migrated]

Context: I wish to know how to get the magnetic field strength (H) in a surface point of the condenser made by 2 circular plates separated by a dielectric which is a perfect insulator with a uniform ...
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Does the solenoid force formula apply to electromagnets?

Related questions: How to calculate the repulsion force between two electromagnets With what force can a solenoid pull? What assumptions does the solenoid force equation make? I am trying to design ...
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What voltage do I need for my solenoid magnet?

I am looking to buy a suitable solenoid magnet for an experiment. The experiment is quite primitive but I do need the right magnet although my knowledge of electromagnetism or electrical engineering ...
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93 views

Endless oscillator [closed]

Can we create an endless oscillator? simulate this circuit – Schematic created using CircuitLab The diodes will only allow a tiny current to move through the tank circuit-> the power loss ...
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55 views

Can magnetic connectors cause dangerous voltage spikes?

I have some magnets lying around and thought about puttin them on the ends of a wire to make a magnetic jumper for my perf board. However, I am aware of the effect of magnets on wires, ie induction. ...
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1answer
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Steel cooker is not a Faraday cage? [closed]

I read that steel/iron/metal/conducting cages, with gaps less than the wavelength of electro magnetic waves, shield whatever is inside from that radiation. But when I put my mobile inside a cooker and ...
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1answer
53 views

Rayleigh distance of array antenna

Far field zone of a single antenna can be determined by using the equation below. $$R>\dfrac{2D^2}{\lambda}$$ Where D is the biggest dimension of the antenna. This equaiton is suitable for single ...
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55 views

How does the shield of a coaxial cable work?

let's consider a coaxial cable with only two conductors (the core and the external metallic shield), and let's consider the case in which it propagates TEM mode at a certain frequency: My question is:...
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56 views

Characersitics of a traveling wave on a half wave dipole antenna

For a center fed dipole antenna when operated at resonance, the AC electric potential applied at the feed point results in traveling waves of AC current which emanate from the feed point out towards ...
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Forward converter - How to measure the equivalent leakage inductane of this model?

Here is the schematic that I found in an old AN from UNITRODE. https://www.smps.us/slup199.pdf Here is the equivalent schematic showing the magnetizing inductance and the leakage inductances: This ...
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44 views

How does current flow in unbalanced antennas?

I have been researching and learning more about antennas recently however I am a bit stuck on understanding how balanced and unbalanced lines / antennas function. My understanding is that a balanced ...
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What is the physical meaning of the dispersion equation of an antenna?

I have a basic doubt about the role of the dispersion equation of an antenna. There are many situations (grounded dielectric slab, optical fibers etc) in which it is written, so I will put here an ...
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Need help calculating resistors for a modular model particle accelerator

I foolishly took on a complicated school project of making a model particle accelerator. The idea was to make it a modular system, as in each segment, or "accelerator module" would be ...
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1answer
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Find the flux leaving the surface of the sphere: What will the position of line charges look like diagrammatically?

I am not able to understand how the two uniform line charges will look like in space. It would be of great help if someone could draw the uniform line charges in cartesian coordinates and upload it ...
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Design spec for faraday cage

I need to build a faraday cage to shield from the following source: 8 Watt, 14 MHz. The signal is AM modulated I want to build an metal box enclosing the source. I want it to shield the signal so that ...
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2answers
60 views

Charge carriers of an electric current

I was under the impression that electric current was caused exclusively by the flow of electrons moving through the wire. However upon doing a little more research on electric current, it is said that ...
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1answer
30 views

Off-the-shelf electromagnet with deterministic pole

I looking to buy an electromagnet (12v) and there are a lot of them out there on amazon and ebay in all kinds of size and shapes -some are round, some are rectangle, etc. However, in my application, ...
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1answer
29 views

Friis transmission equation: how do I consider power loss along other directions?

I do not understand a basic concept about Friis transmision equation between two antennas: where Dt and Dr are the antenna directivities (with respect to an isotropic radiator) of the transmitting ...
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87 views

Does it matter if power is applied only instantaneously?

If I build a railgun and apply say, 1 million watts, to the circuit to try to power a projectile forward through electromotive force, will it really matter if that 1 million watts of power is applied ...
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32 views

Far field radiation and spherical waves

I have a basic doubt about electromagnetic waves emitted by a certain source. Depending on the shape and on the physical properties of the antenna, its electromagnetic waves may have different ...
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27 views

Magnetic field in the center of a coil

I have a closed core with a coil attached to it and metal inside the core. The N is 100, I is 100mA and l = 300mm. I have computed the magnetic field B = (μ0 * μr * N * I) / l. But I have also given ...
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1answer
59 views

Does the letter k in electromagnetics represent wavenumber inside a cosine?

I am having a intellectual debate with a colleague on whether k (in this equation below) represents the wavenumber k (that is used in electromagnetics) or does k in this question not refer to ...
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direction of current densities for electrons and holes?

Let's say we have: \$ J_n = 3 \frac{A}{m^2} \$ and \$ J_p = 2 \frac{A}{m^2} \$ and let's define the direction of positive current (flow of positive charges) to be moving from left to right. Then, ...
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Side lobe level of an aperture antenna

There is a electric field in the far zone of the rectangular aperture antenna as shown below. Antenna lies along the xy plane. $$E_{\theta}=\dfrac{jke^{-jkr}}{4\pi r}\dfrac{sin(0.5\lambda k sin\theta ...
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40 views

Matrix has a voltage drop on a coil that should not be receiving any current

I am making a matrix of electromagnets (each with about 120 Ohms resistance) and I am using a circuit like this for the columns (low side of the switch): simulate this circuit – Schematic ...
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2answers
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Cockcroft walton multiplier output both AC and DC?

I was watching this video https://www.youtube.com/watch?v=ep3D_LC2UzU and I noticed that closer to the end he is probing the upper half of the circuit and the scope is displaying square waves , also ...
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33 views

fastest B field rise time in an inductor/electromagnet

What is the fastest attainable pulse rise time for either a pulse or a square wave using a iron core aka transformer steel laminated core, assuming the laminations are of the best possible quality ...
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4answers
62 views

Energy Transport in Circuits

I've been reading about how energy is actually transported in circuits (I first read about it here: http://amasci.com/miscon/ener1.html). The description in this article of why electrons don't move ...
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1answer
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Skin/Proxmity effects near transformer core

The above picture shows a rectangular wire carrying alternating current wound across a core with permeability much much greater than of free space(and also assumed is the fact that the width of the ...
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39 views

Why does a rotating magnetic field's frequency decrease, if we increase number of poles (induction motor)?

I absolutely don't understand it and drives me crazy. I've found several sources, in which there are shown images and animations about how two or three phase electric current generate rotating ...
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Depletion region (space charge region) width calculation

Calculation of depletion region width requires the knowledge of permittivity of the material as shown below. \${\displaystyle w\approx \left[{\frac {2\epsilon _{r}\epsilon _{0}}{q}}\left({\frac {N_{...
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33 views

Dielectric constant (relative permittivity)

I recently learned that the dielectric constant (or relative permitivity) is not actually a constant, but it depends on wavelength or frequency (dielectric function). If that is the case, why are we ...
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1answer
20 views

In Inductive Position Sensor the air gap between the metal target and coil changes the position value?

I am trying to design the inductive position sensor with the inductive sensor IC ZMID5201. I am trying to optimize the air gap betweeen sensor coil and metal target. As per the datasheet its ...
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1answer
116 views

Designing an EMP Generator for school :^)

How would I go about calculating and designing a circuit that can produce an axial magnetic field greater than 20 Tesla for about 1.4 μs (full width at half maximum). The dimensions of the solenoid ...

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