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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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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
56 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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0answers
815 views

Monitor/screen that blanks due to static electricity in my chair [migrated]

I come to you today for a rather special request, but you may be the best people to answer it. I am a developer and I have an Ikea standing desk (automatic one) in an open space. I have a big static ...
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1answer
47 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/-1.6 mT). Prior to going down a rabbit hole of magnetism in physics, I ...
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6answers
4k views

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
30 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
609 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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0answers
22 views

the role of polarization in signal propagation

What is the role of polarization in signal propagation? Is it important to know the radio wave polarisation for reflection, diffraction or reflection? or for the types of wave ( ground, sky, space)? ...
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3answers
68 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
63 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
141 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
51 views

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
70 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
68 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
26 views

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
194 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 ...
2
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2answers
79 views

“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
74 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
74 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
2k views

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
66 views

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
35 views

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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1answer
29 views

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
41 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
56 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
104 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 ...
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2answers
94 views

How current and potential propagate through electrical circuits?

I have something of a theoretical question. In any given electrical/electronic circuit there seems to be an electric field developed inside (and outside the conductors?) to push the electrons in the ...
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0answers
14 views

Dividing the rotor circuit by slip in induction motor

In this article equation (3), just after figure 5, they divided everything in the equation for current by slip. I understand that current remains the same when doing this, but voltage and power would ...
4
votes
1answer
154 views

What antenna is this?

I just disassembled an external FM antenna designed for an old Asus laptop. I expected to find some circuitry and a monopole or some other simple antenna. However, what I found was the antenna shown ...
2
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1answer
52 views

Are magnetic sensors able to pick up the electromagnetic field inside toroids?

From my understanding, correct me if I'm wrong, the electromagnetic field outside a toroid is 0, but it has a EM field within the shell itself. So my question is can a magnetic sensor pick up on this ...
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2answers
70 views

How would magnetic wire (not magnet wire) affect the inductance of a coil?

Suppose that magnetic wire with resistivity similar to copper but with non-negligible permeability existed. What effect would magnetic wire have on the coil inductance versus a copper coil of the ...
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2answers
102 views

Why does my laptop emit electromagnetic radiation when charging (only)? [closed]

I have an electromagnetic radiation detector that I've been playing with recently, going around the house and testing various appliances, and I noticed something weird. When I charge my laptop (or ...
3
votes
2answers
150 views

What is the mechanism that causes two conductors to “stick together” when a current is passed?

If the positive and negative terminals of certain DC supplies are brought together under certain conditions, the wires will "stick together" with a slight force, feeling almost like they are ...
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1answer
40 views

Difference between a flared and not flared rectangular waveguide antenna

Someone can explain to me the difference in terms of performance between a flared rectangular waveguide antenna (precisely a pyramidal horn) and a not flared rectangular waveguide antenna? In horn ...
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1answer
45 views

Matrix “Multiplexing” with electromagnets, interesting behaviour

I have an interesting behaviour with my electronics project. I am trying to do something like a LED array but with electromagnets instead. See the schematic below. I built the magnets myself by ...
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2answers
180 views

How does a hall effect wheel speed sensor work?

I have been researching how a wheel or crank speed sensor works in vehicles and am having a hard time finding a hard truth. I think I understand how it works simply. That the sensor detects a change ...
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1answer
58 views

Inductance of planar (spiral) coil near solid copper surface

I'm working on a electromagnetic levitation system, consisting of a flat spiral (planar) inductor positioned above a solid copper surface. The planar coil is parallel to the copper surface. (Consider ...
3
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2answers
70 views

Spiral hoar frost and spiral device around telephone or electric landlines

I live in Germany. When I travel by train, sometimes there are cables that run from pole to pole parallel to the train track. From the lack of insulation between wire and pole, I guess these are ...
2
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0answers
209 views

Mistake in published paper about magnetic levitation?

As I was reading through this paper: Nonlinear Model & Controller Design for Magnetic Levitation System, I stumbled cross section 3.3 which I could not follow. Summarizing section 3.3 Non Linear ...
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1answer
63 views

Other than direct radiation, how can RF interference transfer between stacked PCBs?

I have VHF aviation radio consisting of 3 boards stacked upon each other: digital, receiver and transmitter, the digital is on ‘top’ with receiver in the middle, there is thick shielding between the ...
0
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1answer
124 views

Calculating number of coil turns for a generator

I'm building a generator for a school project. I'm planning to use N42 neodymium magnets with performance of 5100 Gauss, How do I calculate what diameter of copper wire I need to make the coils and ...
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0answers
63 views

Reducing electromagnetic interference in underwater acoustics cables

Our college underwater robotics team has a passive acoustics system with four hydrophones that provide an analog signal typically between +/- 200 mV corresponding to the sound wave at that point in ...
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2answers
178 views

Is there back EMF in an induction motor?

I noticed that in deriving the equivalent circuit for an induction motor in the rotor component, that a "variable" resistance was introduced. This really confused me as I didn't understand how power ...
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1answer
53 views

Why do we divide by slip in the Rotor equivalent circuit for an Induction motor?

I was reading this article and everything made sense until the equivilant circuit for the rotor was divided by the slip s. I understand that the current in the circuit would remain the same, but it ...
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0answers
88 views

Dot convention inductors in series: equation confusion

So I'm really confused with mutual inductors and dot convention. If your answer is going to be a link to any website I can assure you I read them all and that only left me more confused. So here are ...
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1answer
19 views

Confusion about the direction of the vectors: motional EMF

I'm working through an example with motional EMF and I'm having trouble understanding the directions of vectors so that I can apply induction law. The magnetic circuit seems complex because the ...
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1answer
51 views

Energy loss by Hysteresis

I recently did an experiment aiming to verify the magnetization curve of the cores of a single-phase electrical transformer. I applied a sine within one core and I observed this one and the other one ...
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1answer
53 views

Solenoid Force Vs Amp-Turns in Saturation Region

I'm trying to understand solenoid behavior through the magnetic saturation region. Most solenoid charts show a linear force vs current: This doesn't seem to show any saturation. I assume that's ...