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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37 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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2answers
6k views

Why don't electrons take the shorter path in coils?

Below is a copper coil, presumably forming an electromagnet. From my understanding the electrons travel around the coil to produce a magnetic field. But why don't the electrons jump the wires and take ...
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17 views

High speed switching electromagnet control circuit

I am not very familiar with high speed switching magnets, and need help finding a control circuit that has adjustable frequency and duration for High Rate Switching Electromagnets, with a digital ...
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1answer
45 views

Telephone Call and Electromagnetic Waves [closed]

Can you give me a simple explanation of how do telephone calls work? I know that when I receive a telephone call, it means that my mobile has just received a certain Electromagnetic field. But in air ...
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3answers
957 views

Why doesn't a commutator cause the rotation to reverse periodically or stop?

I understand the field magnets attracting/repelling the armature/coil so that it turns one half-turn and then, because the commutator is turned, its contact with the brushes has switched sides, and ...
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51 views

why stepper motor lose magnetism?

I have very old desktop style 3 axis cnc machine. There were 2 dc motors for X-Y axis and a unipolar stepper for Z axis. I replaced the old DC motors with unipolar steppers. I personally made the ...
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40 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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48 views

Interpreting this bode plot

I ran a frequency analysis on a conductive textile I have designed and I am not sure what to make of this bode plot. My background is in textile design, not engineering. Does this make sense to anyone ...
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2answers
76 views

DC Series motor and its starting

I studied electromagnetics and with that understanding when I recall the Working of DC Series motor I stumbled upon an inherent negative feedback action in the DC series motor during starting as ...
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1answer
34 views

Field Flux control and Speed Of DC motor

I was studying electromagnetism and I tried to link with working of DC motors. For the speed control of DC motor - The Flux of DC motor is reduced to increase the speed above rated speed. I ...
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4answers
65 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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46 views

How am I supposed to calculate the half power beamwidth of antenna (HPBW) from radiation intensity?

I know we should set the U equation = 1/2. But am I wondering should we just set the cos^4(theta) = 1/2 or the whole equation including the constant number 200 i.e. 200cos^4(theta)=1/2 to solve for ...
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3answers
83 views

How does one position control a voice coil actuator?

I am looking at trying to position control a voice coil actuator (something like these). On the end of the voice coil actuator will be a small load (let's just imagine a 10 oz cube), screwed onto the ...
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1answer
23 views

Guided propagation in transmission lines

Can you help me on understanding why we may say this transmission line the propagation is guided and there is not any radiation? It is a 2-conductors transmission line, in which the conductors are ...
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1answer
80 views

Switching 10 contacts with one switch

I am looking for a way to switch 10 contacts but without having to switch these tiny contacts one after another. So basically one movement, 10 contacts open/close. I saw this little switch: But ...
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36 views

Calculate electric field from wire with AC current through

Here an experiment picture The wire(with some resistance) connected to 220 V 60 Hz AC voltage source. The peak current through wire is 0,3 A How to calculate mean, or at least peak electric field ...
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19 views

Complex vectors E and H

I have a doubt about the physical meaning of the complex representation of electric and magnetic fields. Let's consider an electromagnetic wave, in which both electric and magnetic fields propagate ...
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18 views

Power Radiated by an antenna

I have read that the power radiated by an antenna is equal to the flux of the Poynting vector through any closed surface that includes the antenna. This fact is for instance exploited to calculate ...
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41 views

Guitar pickup wiring question

I have an older Seymour Duncan vintage rails pickup. Part number SVR-1N-0309. This model only has two wires, red and white, compared to the new versions. Unfortunately, Seymour Duncan doesn’t seem to ...
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1answer
44 views

Tungsten Halogen Globes

The tool shed of my current residence has holes in it, and it rained heavily the last few weeks, during which the expected outcome of one of my flood lights blowing a fuse occurred. I don't want to ...
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2answers
76 views

Does an AC wave running through a wire produce EM waves?

I understand that current from a DC source running through a wire produces a magnetic field. However, is the changing magnetic field produced via current from an AC source, technically a part of a EM ...
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1answer
25 views

Insertion of transmission lines and effects on reflection coefficient

I have a doubt on a step usually performed in matching network design. Consider a load ZL: a method for getting impedance matching (for instance with an amplifier) is that of inserting a transmission ...
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1answer
34 views

Coulomb’s Law and divergence

Assume there is an infinite line charge. Therefore, it has an electric field around it. If we calculate the divergence of the electric field \$\mathbf{E}\$ caused by the line charge, what is the sign ...
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2answers
81 views

How should I make a constant AC current source to drive an electromagnet?

The inductance of the electromagnet is about 0.05H and the resistance is under 50 Ohm and I need about 2 to 5 Amperes to drive it. I need to be able to change the amplitude and also the frequency at ...
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1answer
57 views

Dot convention meaning

I have two questions about dot convention for the ideal transformer. I have understood how to use them in writing the voltage drops on the coils, but I have some doubts: 1) Which is the physical ...
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1answer
86 views

How to design a contactless mechanical shaker [closed]

I am trying to design a circuit to make an inductor oscillate with high-current (around 50A) at a low frequency. The inductor will act as a high-powered electromagnet. Most designs I've worked/messed ...
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1answer
36 views

Magnetic Monopoles and Magnetic Current Densities

I see that in electronic engineering the Maxwell equations are written with also some terms which represent the magnetic charge and the magnetic current densities. I was told they are inserted only to ...
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0answers
62 views

Avoiding signal interference in a cable that carries video signal and sensor signal

I am using a 6 core shielded cable. In this 3 wires are used for a sensor and 3+1(shield) is used for a analog camera. All the cores take DC supply. Sensor(3 wires) (+)24 volt supply, (-)minus, ...
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3answers
46 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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1answer
14 views

Voltage/Current waves on N port networks

I have a doubt about the sign convention for waves in an N port network. Consider for instance the following 2-port network: How should I fix the directions of voltage and current to calculate powers?...
2
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1answer
40 views

Quarter-wave impedance transformer working principle

consider the following scheme: A transmission line of length lambda/4 has been put before the load ZL in order to get an impedance matching. But, I do not understand how it works. Precisely, by the ...
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2answers
108 views

what if the two wires of a single twisted pair are different in length?

For example, one wire of a twisted pair is longer than the other wire (imbalance starts from the middle of the twisted pair, everything is balanced before the middle point). What problems will it ...
2
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1answer
64 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 ...
4
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2answers
100 views

Why is the the permeability of a ferromagnetic material given as B/H not it's slope dB/dH?

I was going through my Electromagentics book by Sadiku where it was mentioned as a point that permeability of ferromagnetic material is given by the ratio of B(magnetic flux density) to H(magnetic ...
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4answers
153 views

Is the curl of a B field at a point on a wire infinity?

According to this text, curl is defined as a limit of the surface area approaching zero. If the point where the curl is evaluated at is near the wire, B is evaluated at a decreasing r value, and ...
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2answers
199 views

Am I exposed to high levels of radiation at my job? [closed]

I made this post because I have a safety concern about my job as medical device tester. I was reading the user manual of the equipment I work with and found the next warning: “Per FCC regulations, ...
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1answer
44 views

demagnetising a magnet with a high frequency transformer

This is a theoretical question. Some elements described in the problem may be impossible/impractical, but I am just trying to understand the principles. It is kind of a physics question, but also ...
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0answers
14 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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1answer
63 views

How to transmit a signal to a point [closed]

I have a signal generator (Digital Dual Channel Funktion Signal Generator) and want to generate two signals (530 and 550 Khz signal) and want to transmit these generated signals to the points on a ...
0
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2answers
86 views

Can a change in magnetic field change the impedance of a coil

I kept a coil in a linearly increasing magnetic field and calculated the impedance by measuring the induced current and voltage. When the maximum value of magnetic field was reduced (while keeping ...
0
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1answer
73 views

signal propagates in bending transmission line (unequal length between signal path and return path)

Suppose I have a square wave signal generated from a signal generator and its outputs are connected to the two terminals of a paired PCB traces (left side of the picture below). The other end of the ...
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0answers
20 views

How flux density increases in the dielectric medium?

The above figure shows a polar dielectric medium in an external electric field which is normal to it's surface. From the equation of D(electric flux density) we see that flux density increases but ...
2
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1answer
94 views

Inconsistent readings between oscilloscopes

I have a circuit that pulses a high frequency EM field at a rate of 2Hz. I'm trying to see the accuracy and precision of the circuit, but I see very different readings on two oscilloscopes I'm using: ...
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0answers
27 views

Antenna Polarization understanding

I am trying to design a Circular polarized Antenna. We know that the criteria for a circularly polarized E-field : The E field should have to components The two components should be equal in ...
1
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1answer
18 views

PEC-backed dielectric material

For the paper named "Antenna Miniaturization and Bandwidth Enhancement Using a Reactive Impedance Substrate" the statement "PEC-backed dielectric material", so what is the meaning of this statement? ...
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1answer
39 views

Lorentz force of a conductor loop

I have a task to solve in electrodynamics, I have really no clue how to solve. Would be very thankful if someone could help! There is a live conductor loop L, which is situated in a magnetic field B. ...
2
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3answers
245 views

Making a electromagnet

Can a insulated wire be used to make a electromagnet? Will there be any difference in strength of the magnet if I use an uninsulated wire instead? By uninsulated wire I mean this:
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1answer
28 views

Field geometry of external magnetic core?

If there is a coil with an external core, would the polarization of the magnetic field inside it be the opposite of an internal core? For example, in the image: If DC current were applied to the ...
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3answers
200 views

Physics of Dirty Electricity? [closed]

I've been reading about "dirty electricity" lately and while I know there's much controversy whether it causes adverse health effects this question is not about that subject. I'm simply trying to ...
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0answers
22 views

current transformer and primary positioning inside window

I am designing a setup that is a little convoluted. but it's on purpose. The point is to make a toroidal current transformer act as an electromechanical pickup. Just for musical experimentation and as ...