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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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Electromagnetic Repulsion Coil Calculations

We have a 3x3 mm circular thin plate, which is made of copper, aluminium similar materials and thickness of the plate is 1 mm i.e. a very light and small piece of metal. To lift this plate about 2 mm ...
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2answers
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Is there a motor design where a rotor gradually moves into a stater?

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,...
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3answers
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Copper wire current ratings

I have seen a wide variety of different estimates for the maximum current rating for copper wire. For example, for 24-gauge copper wire, the Wikipedia article about "American wire gauge" claims that ...
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4answers
39 views

How do you drive a variable reluctance stepper/SRM as a generator?

I think I understand the principles, even if not the details, of operating a VR/SRM as a motor. But I don't understand, and can't find any good explanation online of, the principles for how to use one ...
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Why can't \$ε_r<1\$? [migrated]

I've heard it said that the vacuum permittivity is the lowest possible permittivity for any substance, that no substance can have \$ε_r<1\$. Is this true? If so, why is this different from ...
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1answer
24 views

Is a one-stator reluctance motor possible?

Often when the magnetic field of reluctance is pictured, one sees a "flow" from one stator to another across the rotor. I'm wondering if it is possible to have a reluctance motor with only one ...
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30 views

How to stabilize the magnetic levitation system? [duplicate]

I have asked similar question before also but want to try again - Not able to levitate magnet for magnetic levitation project I followed everything from this project but still, the magnet is not ...
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60 views

Given that \$ \mathbf J =10^4(x^2+y^2) \mathbf a_z \$ \$ A/m^2\$ , determine current density, volume charge density at the given points

Given that \$ \mathbf J =10^4(x^2+y^2) \mathbf a_z \$ \$ A/m^2\$ , determine (a)The current density at (-3,4,6). (b)The rate of increase in volume charge density at (1,-2,3). (c)The current ...
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35 views

Can I use a power supply to power a solenoid electromagnet?

I've got several unused coils of 14 gauge wire that have ferrite iron cores cut to the length of their spools. They have maximum current power transmission ratings of ~5.9A, and according to a ...
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0answers
37 views

Problem based on Laplace and Poisson's Equations. How to find the charge from electric field and potential?

In the above problem, I have found out the potential and the electric field in the medium between the two conductors. From here, how can I calculate the approximate charge per plate?
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Given the vector current density, determine the total current flowing outward through a circular band

Given the vector current density, determine the total current flowing outward through a circular band.: The answer should be 518A. It comes something around 3255 A. Where is the mistake?
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Find force pull solenoid

Sorry for the previous post that was wrong. I want to knowF=(NI)^2*μ0*A/2L^2 A What is the cross-sectional area? NewRef.https://www.researchgate.net/publication/...
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1answer
69 views

What is the major difference between the Telegrapher's Equation and the transmission line equation?

I am confused on when you would use the telegraphers equations vs when you would use the transmission line wave equation. Telegraphers equations: Transmission line wave equations:
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1answer
49 views

Reflection of Electric field in open-circuited transmission line

Consider a parallel-wire or parallel-plate or coaxial transmission line, carrying TEM wave, which we model as E,H,V,I, each having a forward(+) and backward(-) wave. In terms of V,I, we define ...
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1answer
49 views

Different printed circuit layout for a transistor

The below figure shows a schematic for a transistor where there exists an external magnetic field : This schematic has two layouts to choose from. The first one is shown below : The second layout ...
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0answers
38 views

How does a electropermanent magnet work?

I’m trying to wrap my head around electropermanent magnetism. I read this wonderful PhD Thesis by Ara Knaian as well as details the history of this concept as well as Kyle Gilpin, Ara Knaian, and ...
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0answers
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What's the circuit diagram symbol for a variable reluctance sensor transducer?

I know I've seen the symbol before, it's something like a circle with an open triangle facing in the direction of current flow with a line through the middle. I'm specifically thinking of the ...
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3answers
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Why current flows along a transmission line?

Say I don't have a ideal transmission line i.e resistance/length!=0. Also E-Field exists between the two conductor lines. How then current flows through the line? There is no E-Field along the line ...
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4answers
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Why does magnet wire need to be insulated?

What is it about having multiple coils that enables the magnetic field? Why can't I just have one big wire or threaded wire on a motor? Sorry, it's kind of a baby question but I couldn't find the ...
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1answer
76 views

Why does adding more coils make my electromagnet weaker?

I've built a couple of simple electromagnets, using a nail (not sure of the material) and copper wire connected to a 1.5V AA battery. I'm really confused because the electromagnets with less coils are ...
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2answers
78 views

Increasing current in an Arduino circuit?

I'm trying to power a small electromagnet using my Arduino Uno, but when I use the 5V pin, the current flow is not enough and the electromagnet ends up being a lot weaker than it is with a regular 1....
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2answers
87 views

Is wire-wrap spacing and consistency important in electromagnets?

I'm creating an electromagnet (several, actually) to test a hall effect switch. I understand that more wire wraps (turns) increases the magnetic B-field, as does more electric current. Adding more ...
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1answer
23 views

Absorber effect on EM RF pattern

If I have an omnidirectional antenna and put a perfect reflector plane near it (in the near field), it will obviously change its radiation pattern in the direction opposite the reflector. ...
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0answers
16 views

Magnet effect on Eddy-current Testing

If someone is doing Eddy-current Testing on a weld near a large and powerful magnet, in contact with the part near the weld, will this have any effect on Eddy-current analysis? If it does effect the ...
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2answers
68 views

How do I convert the units of a moving magnetic field to volts?

Copper wire wrapped around an iron core produces current when a strong magnet is moved in its vicinity. I gather the "magnet movement" part is expressed in units of "weber" (kg⋅m2⋅s−2⋅A−1) or perhaps ...
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2answers
64 views

Must the air gap in a transformer always be perpendicular to the magnetic field lines?

The air gap in a transformer seems to always be spaced across the cross section of the core, where the magnetic field in the core has to then flow across it. Since the core is typically made of ...
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2answers
72 views

How can I test a Hall effect sensor at a given distance?

I have a project that includes an Ablic S-5716ACDL1 omnipolar Hall effect switch. It has a sensing range of about 3 mT (±1.6 mT). Prior to going down a rabbit hole of magnetism in physics, I ...
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6answers
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Can antennas be viewed as light sources?

Clearly antennas are nothing but a device to radiate the electrical energy through electromagnetic waves. Since visible light is also simply a certain range of frequencies, isn't it more easier to ...
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0answers
31 views

Electromagnet design for 20Hz-20kHz AC

I am trying to design a U core electromagnet to pluck a ferromagnetic guitar string. The strings would sit at the outside center of the U core. I am wondering if high flux cores are ok for this ...
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2answers
622 views

Conversion of a transformer into an electromagnet

Is it possible to convert a voltage transformer into an electromagnet by connecting a small DC voltage source to its primary side?
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4answers
102 views

Sinusoids represented using Euler's formula notation, confusion

EM plane waves are represented using the equation (ignoring amplitude) $$E(x,t) = e^{j (wt - kx)}$$ They are also represented in this form: $$E(x,t) = \cos(wt - kx)$$ I want to get the electric ...
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1answer
64 views

Find Voltage induction flux through the circuit

Find the max voltage induction on this figure. Ok. My doubt is: Consider that a << d like the question said: So what have I missed on my analysis? If I want to solve this questions and ...
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3answers
143 views

As we go around the circuit, the total voltage drop must equal zero

I am studying an advanced mathematics textbook. One of the examples is within the context of an electrical circuit (a series circuit, I think). The example makes the following claim: As we go ...
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2answers
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What causes the residual magnetic flux when the current is zero in an inductor hysteresis curve?

An inductor with hysteresis has the following current versus flux curve: I marked the point in red where the current is reduced to zero but there is still flux on the above curve. What really causes ...
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2answers
74 views

Three voltage sources circuit

Suppose the given circuit, find the current through the resistant R2 given that: E1 = 3 V E2 = 4 V E3 = 2 V R1 = 1 Ω R2 = 6 Ω I tried to apply kirchhoff laws but it was hard given such ...
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1answer
71 views

Detect if an electromagnet it touching metal (without a switch)

I have a simple 12V DC holding electromagnet connected to a microcontroller using a MOSFET - the once you buy on aliexpress or eBay for cheap [1]. How can I detect if the magnet is in full contact ...
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3answers
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Making a parallel connection = increasing the total current?

Considering the scheme below simulate this circuit – Schematic created using CircuitLab Am, I understand correct, in real life, if I will step-by-step add the parallel resistors, the total ...
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4answers
198 views

What happens to the energy stored in a short-circuited capacitor?

Suppose we have an ideal capacitor with a certain voltage between its plates. We connect the two plates using an ideal (lossless) wire, so the capacitor discharges. Where has the energy having been ...
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2answers
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“Electromagnet 5kg DC 3V 5V 6V 12V” - what do these multiple voltages mean?

I wanna buy an electromagnet from aliexpress and many of them are lifter magnets and have 6V, 12V, 24V and 5kg. So if i choose the 6V option does that mean the magnet can lift 5kg at 6V? Why would ...
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1answer
80 views

Why does the self-inductance of a straight wire decrease when its radius increase?

I made some research on the self-inductance of a straight wire, and many sources cited “Inductance Calculations” of F.W. Grover. So I read a bit of that book but I couldn't find the answer to my ...
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2answers
85 views

Do rail gun systems require high voltage?

I couldn't justify, as to why most rail-gun examples I found would have high current and high voltage. When the rails & projectile can be designed to have low resistance by varying the volume of ...
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14answers
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How is it that two electric currents can travel in opposite directions on the same wire, at the same time, without interfering with each other?

An Introduction to Information Theory: Symbols, Signals and Noise, by John R. Pierce, says the following: While linearity is a truly astonishing property of nature, it is by no means a rare one. ...
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4answers
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Improvised inductor core ideas

I was wondering if anybody could suggest some common items around the house or at the hardware store that would make a passable core for an inductor. Or items that I could salvage material from. For ...
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2answers
74 views

What would happen if a rotatable ferromagnetic rod were placed beside a magnet?

If one were to place a rotatable shaft (green circle), made of plastic with ferromagnetic material (grey circles inside green circle), right beside an electromagnet, what would happen? I am trying to ...
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1answer
83 views

Can you turn a key stuck on the inside of a door from the outside using an electromagnet? [closed]

i got woken up by a horrible sensation of being blasted by pulses of radiation and ringing ears this morning, followed by short period of silence and then the sound of the cellar door next room ...
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2answers
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How to calculate induced current?

Suppose we have a closed loop with two resistors in series and at particular moment in time the induced emf was two volts .i want to know why do we use ohm's law in calculating the induced current ?
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How to determine direction of induction current (I inc) according to V emf?

In this question, I easily understand the solution. But I want to determine the direction of induction current (I inc) with the Lenz Law. I know how works Lenz Law, but I couldn't determine the ...
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2answers
54 views

Determining magnetic flux density of a closely wound toroidal coil

I am using David K. Chengs's Fundamentals of Engineering Electromagnetics book. In chapter 5/question 5.2, there is a given closely wound toroidal coil, and it asks what is the magnetic flux density ...
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1answer
58 views

Why do two antennas have to have the same polarization?

I have a linear horizontally polarized transmitting antenna and a dipole antenna, polarization mismatch losses can be approximated by 20log(cos(x)) where x is the misalignment angle. What is ...
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2answers
113 views

Clarification on This Transformer Statement

Secondly, when the current starts to rise in the secondary wire, the magnetic field it generates is multiplied by the loop count. Obviously if we had lots of loops, a very small current will ...