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.

201 questions with no upvoted or accepted answers
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140 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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1answer
62 views

Is there any way to wind this 4 pole motor to behave as 2 or 8 poles properly?

I got an induction motor in a junkyard, a WEG motor made for an Electrolux washing machine. It is a single-phase 1/2 hp 4 pole motor. It runs in 127 V and has a 40 uf capacitor feeding the auxiliary ...
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1answer
137 views

Radar and Standing Waves

I have a doubt about the working principle of a simple Radar. Consider a stationary object, which does not move with respect to our transmitter. We send an electromagnetic wave to it, and it will ...
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1answer
84 views

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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2answers
88 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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68 views

System of multiple conductors: image method

The problem statement, all variables and given/known data The following figure represents the traversal cut of a system with two cylindrical equal conductors of radius r0 length l at a distance d ...
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1k views

Building an electromagnet to work over an air gap

I am currently working on a project where I am building an electromagnet that works over an air gap. Specifically a gap of about 0.3 inches. The electromagnet type was selected because I need to be ...
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64 views

Problem with switching solenoid valve by relay

I've been trying to drive a 12volt solenoidal valve with a 5volt relay .Relay is working perfectly for driving normal loads(light bulbs).But it is not driving my 12volt solenoidal valve. I've already ...
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72 views

Analytically understanding wireless power transfer

https://youtu.be/M8aZoM9p43k This YouTube link shows a experiment I quickly made. Two resonant lc circuits that use magnetic fields to wirelessly light up a led. I manually found the best frequency ...
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2answers
92 views

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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28 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
34 views

Attenuators in Waveguides

Let's consider for instance a rectangular waveguide with TE01 mode. As shown here, a possible attenuator may be realized with a metal card placed so that it is tangential to the electric field. Here ...
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274 views

Intuition behind transit angle of a klystron

What I understand is that the electrons get attracted to the anode and during their passage through the buncher gap, they regroup into bunches due to differing potentials imposed on different ...
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386 views

In an induction cooktop, what happens to the coils resistance when there is no pot? Does it vary between pots? How does the appliance respond?

An induction cooktop (or an induction rice cooker) uses a copper coil with a high-frequency alternating current going though. The magnetic flux heats any iron-alloy pot placed above. But what ...
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2answers
267 views

Homemade electromagnet parts

I'm trying to build a homemade electromagnet to show my son. I took speaker wire and wrapped it around a stick maybe about 40 times. Then I used a C cell battery to power it, however I saw no magnetic ...
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2answers
72 views

What are the consequences of not having a magnetic field in the atmosphere on electronics?

Electronics super-noob here! (I did EE in school but have managed to forget practically everything since, to an alarming degree!). I'm wondering how the field of electrical engineering and electronics ...
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42 views

Loop inside a loop, where is the mutual inductance greatest?

I had a question while working a problem as to where the mutual inductance of a circular loop inside a rectangular loop is greatest. Is it at the center, because the magnetic field of all four wire ...
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35 views

If \$\vec A=3\hat a_r+2\hat a_{\theta}-6\hat a_{\phi}\$, determine the vector component

If \$\begin{aligned}\\ \vec A=3\hat a_r+2\hat a_{\theta}-6\hat a_{\phi} \text{ and } \vec B=4\hat a_r&+3\hat a_{\phi}\\ \end{aligned}\\\$ determine a)\$\vec A.\vec B\$, b)\$|\vec A\times\vec B|\$, ...
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44 views

Do the bremsstrahlung radiation size depends on the size of the accelerator?

According to https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf HERMES III, a 16 terawatt pulsed power accelerator at Sandia National Labs, which fired electron beams with peak energy at 22 MeV and ...
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28 views

Is mmf the same as the magnetic force?

In the following system, I created the following equation in terms of what I assumed to be the force acting on the movable object with a mass M. The reluctance of the core is neglected, so the total ...
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29 views

Testing the strength of a B filed from loop of wire and limitations of a function generator

I built a coil that receives magnetic fields (Rx) from a sending coil (Tx) a few centimeters away. (wireless power transfer) I send waves to the Tx at the Rx's resonant frequency since its a loop with ...
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33 views

Left Hand Rule vs Right Hand Rule and the Resistance Generated

Some say that Hall effect takes place prominently only in semiconductors because their impurities create resistance in the presence of magnetic influence, but in case of conductors like copper such ...
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29 views

How to determine proper capacitors to replace a battery for an Apple Magic Trackpad 2?

I have several Apple Magic Trackpad 2 devices and am finding that the batteries routinely go bad on these. They swell and deform the trackpad such that it doesn't stay flat with the desk / tray ...
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29 views

Forward and Backward Crosstalk

I have some basic questions about crosstalk. My reference for this question is this website. This website introduces crosstalk in this way: Crosstalk is the unwanted coupling of energy between two or ...
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33 views

Open termination, signal propagation, transmission lines

I'm inexperienced with transmission line theory so I have a question about implications of signal travel time. Most of what I've read so far has been on lossless transmission lines, not sure how ...
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90 views

Why equal sign was used for limit outside of external conductor?

Why limit is r >= b when magnetic induction is zero instead of r > b? Example: An air coaxial line made of copper (μ ~ μ0) is given. A constant current I flows through the inner conductor. The ...
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27 views

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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42 views

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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43 views

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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0answers
41 views

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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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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27 views

Radiation pattern and propagation direction

I have a basic doubt about how to read a radiation pattern. Let's consider precisely the power pattern: it represents how the power is distributed along all directions in space. For instance, this ...
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2answers
70 views

Electromagnetic compatibility problem with an hairdryer

I wanted to ask you if you could give me an explanation of this electromagnetic compatibility problem. I connected my (fully working) TV to a certain electrical socket in my house. I have also a ...
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0answers
95 views

Is a rotor of an electrical motor charged with electricity?

This might seem to be dumb question, but as far as I understand it: An electrical motor is made of a rotor and a stator. The stator is electrically powered: it has a solenoid and current passing into ...
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2answers
121 views

Why does rotor of synchoronous generator accelerate during faults?

I don't understand the electrical torque in a generator. Isn't the counter torque related to the armature current in the generator? Why does electrical torque decrease during fault in lines that ...
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36 views

Why current distribution of a receiving dipole antenna depends on incident frequency?

When an incident EM wave hits the antenna, the electric field is parallel to the whole wire and start moving all electrons on it simultaneously. I understand that the current at the ends should be ...
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29 views

Parabolic wave equation, electric and magnetic field definitions

The split step solution for Parabolic Wave Equation (PWE) applied to the tropospheric propagation problem is: $$u(x+\Delta x, z)=e^{ikM(z)10^{-6}\Delta x}\mathfrak{F}^{-1}[e^{\frac{-ip^2\Delta x}{2k}}...
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1answer
60 views

Confusion between Faraday's law and Kirchoff's circuit law

Consider a voltage source V connected to a coil. By Faraday's Law e=-(dƛ/dt). I don't understand the direction of the induced voltage e making v=-e However, if we treat the coil as a circuit element ...
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66 views

What is the impact of Earth's magnetic field polarity on consumer electronics?

Earth's magnetic poles are known to have inverted in the past. How are commonly used circuits or component of consumer electronics (from energy production/transportation to TVs, mobile phones and PCs) ...
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38 views

How is voltage induced in Yd transformer without neutral connection sinusoidal?

Thia is regarding bank of 3 single-phase transformers having star connected primary with isolated neutral and delta connected secondary. I know that for bank of 3 single phase transformer core flux ...
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0answers
118 views

Inductance of a single conductor

Which is the correct expression for the inductance of a single conductor? I see 2 different formulaes for the same in different sources. Formula 1. Ref: https://www.eeweb.com/tools/wire-inductance ...
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1answer
77 views

Get expressions of E and H fields at a boundary from expression of surface current - Pozar ex 1.11

I am bringing whis question because, even though I have the solutions manual from the exercises of the book "Microwave Engineering 4th edition", by David M. Pozar (one of the Bible books for microwave ...
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55 views

What's the name of the force that opposes the movement of magnet trough a coil?

I am trying to make an experiment that looks like this: I am using this source https://physicshandson.wordpress.com/2019/02/04/damped-oscillations-in-mechanics-and-electromagnetic-induction/ as a ...
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51 views

Can we apply the equivalence principle in electromagnetics to multiple regions simultaneously?

Setup 1 An object \$(\epsilon, \mu)\$ occupies volume \$V_1\$ and is enclosed by surface \$S_1\$. It sits in vacuum \$(\epsilon_0, \mu_0)\$, denoted by \$V_0\$. In \$V_0\$ there is an electric field \...
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47 views

Can an electromagnet sense magnetic load on it?

Say I have an electromagnet, and I put a permanent magnet next to it, the fields repelling. Is there a circuit that can be created that will detect the magnetic load on the electromagnet produced by ...
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4answers
95 views

Momentary Over-Excitation Voltage Circuit

I want to control an electromagnetic brake (fail-safe brake) used along with servo motor. Microcontroller will control the trigger signal for the electromagnet coil. Electromagnet Requirements: ...
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3answers
187 views

Microstrip propagation mode

I have a trivial question about EM propagation in a microstrip line. Why do the electric and magnetic fields have the following lines? Which are the physical laws (Maxwell etc) for determining them? ...
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0answers
112 views

HFSS SAR anlysis Calculation

I am calculating The SAR anlysis on a human head of a wearable antenna that i have made . I have added a waveguide port and after simulation it does not show the radiation pattern using the HFSS ...
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0answers
275 views

Moving a capacitor in a time varying or non-time varying magnetic field?

1) If a simple parallel plate capacitor connected to a circuit, and discharging, were to move in an exterior magnetic field, what would happen to the interior region? Interior region components: ...
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1answer
89 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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