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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 ...

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1answer
62 views

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

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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1answer
38 views

Ultrasonic sensor? [on hold]

I am in search of an ultrasonic sensor that can measure through multiple objects. I am specifically looking at a sensor that can penetrate through metal and to the other side of it. I want to receive ...
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2answers
29 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
25 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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0answers
13 views

How to choose contour when finding magnetic flux density?

In this question, how we decided to use such this contour? Also, why integral (B dot dl) the outside and sides parts are zero? At the outside part; contour and B are parallel, because of their dot ...
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2answers
34 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
39 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
97 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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0answers
18 views

Wave propagation in general media [closed]

Any resourses for wave equation in general media? solving the wave equation equiphase surface and equiamplitude surface
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2answers
85 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
13 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 ...
3
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0answers
78 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 ...
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0answers
18 views

Frequency of electromagnetic wave [closed]

How can we find the frequency of an electromagnetic wave given the magnetic feild intensity H?
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1answer
48 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
67 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
95 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
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2answers
145 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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0answers
26 views

How does compensation windings help to maintain the motor torque?

I know he armature flux superimposes with the main field flux and, it disturbs the main field flux, to reduce this so called armature reaction, the DC motors are provided with compensation windings(on ...
1
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1answer
34 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
43 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 ...
1
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2answers
76 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 ...
1
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1answer
37 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
56 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 ...
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0answers
9 views

Electromagnetic field propagation in any medium at high frequency [migrated]

I am trying to understand an important concept regarding the propagation of EM fields in materials at high frequencies, which is: "At high frequencies any material behaves as a dielectric material. ...
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0answers
21 views

EM wave in different Mediums

In "Perfect Conductors": Electric field can't exist. But Magnetic field can exist. In "Perfect Dielectrics": Which field(Electric or Magnetic) exist and why?
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0answers
174 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
59 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 ...
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0answers
23 views

Dynamic rolled-supercapacitor & Lorentz force & Induction?

I've been designing certain components that would have a supercapacitor attached to a movable (rotation/linear) element. The element is conductive and carries the current from (discharging state) the ...
0
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1answer
46 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
59 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
93 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
48 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
61 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
18 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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0answers
33 views

Calculating distance from magnetometer to electromagnet

I want to calculate distance (and then triangulate to get position) of an electromagnet using multiple magnetometers. It has already been done from the Finexus project , but the formulas are not well ...
2
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1answer
49 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
34 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 ...
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0answers
78 views

Electromagnetics: How would the following wave look like \$ \mathbf{E}(x,y,z,t)=E_0(x)e^{j \omega t} \hat{x} \$

I am studying solution of the wave equation in electromagnetics. I am not able to understand how the following waves would look like; i.e on which plane they are and in which direction are they ...
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2answers
83 views

Transformer magnetizing inductance

I am learning about transformers and in the equivalent circuit the magnetizing inductance of the excitation branch is supposed to represent the current needed to "set up" the flux in the core due to ...
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1answer
73 views

How does a rocking arm voltage regulator work?

I am trying to determine the suitability of replacing a (ancient) rocking arm voltage regulator with a modern digital device. I assume a rocking arm regulator has an electromechanical or magnetic ...
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0answers
35 views

The effects of magnets near a switch circuit?

I'm comparing my options on how to engineer something, and I'm looking for advice on whether to even continue considering this one particular option. Is the use of magnets of any strength in the ...
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0answers
44 views

What should be the resistance in an electromagnet in a household toaster?

I have a faulty toaster, and have measured the 'resistance' across the electromagnet which holds the latch down. Said resistance is 245ohm. Is this reasonable, or would it suggest that the ...
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0answers
49 views

A few questions about copper coils, magnets and induction

So I've been into electronics and electricity in general, lately. I've been trying to understand induction. Here's a few questions I had pertaining to it. In what way are coils connected together to ...
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1answer
41 views

How can a magnetic circuit with an airgap have a higher e.m.f in the secondary coil than the same circuit without the air gap?

I have a magnetic circuit with the same configuration as in the image, the primary coil has 203 turns and the secondary has 406 turns, how do I get a higher eletromotive force when there is an air gap ...
3
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1answer
59 views

Drift current in PN Junction

Ok guys, first of all thanks for your support and your help, I can't understand how the drift current work, let's say that we have this junction By the definition of the drift current we can ...
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1answer
65 views

Can a coil gun be made with a boost converter instead of caps?

So I’ve been starting to build a coilgun, and I find most designs either have capacitors or are just really bad. But could a high-voltage boost converter (40000v) and a momentary switch not be used to ...
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1answer
34 views

Odd step in derivation of phasor Telegrapher's equations

In the derivation of the phasor form of the Telegrapher's equations (in "Fundamentals of Applied Electromagentics" by Ulaby), there is a step I'm not following: When going between eq. 2.16 and eq. 2....
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4answers
109 views

Does the EM radiation from AC power lines propagate through air or is it fixed around the line?

Because of the AC current flow, there is a changing magnetic field around the conductor, that in turn induces a changing electric field and vice versa But does the EM radiation get "loose" from the ...
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2answers
65 views

Can you turn two inductively coupled conductors into a transformer?

So I'm working on a school project, and to be honest. Don't know a lot about electromagnetism. I want to make a wireless charging station that could be plugged into the outlet. Of course I don't want ...
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2answers
35 views

Area of iron core to lift a certain amount of weigh(magnet/solenoid)?

I've been wondering and testing selfmade magnets by wrapping iron with wires and applying a voltage to it which makes it a bit magnetic. I've been looking around the internet and can't seem to find ...