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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Polarization of an electromagnetic wave

How can I find polarization of an electric field as shown below? $$\vec E (0,0,0) = \vec a_x E_{0x}+\vec a_y + 2j \vec a_z \dfrac{V}{m} $$ The propagation of the wave is as shown below. $$ \vec a_n = \...
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Dipole antenna resonance frequencies

let's consider a simple dipole antenna of length L. The following picture refers to a half-wave dipole: In general, at different frequencies, it's known that different modes are possible. Precisely, ...
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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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Calculating the unknown charge using the \$2\$ remaining charges in this arrangement

The overview of the problem and the solution and my thoughts are as below. "/*" represents about my comment. We'll handle the \$3\$ point charges in the vacuum. Firstly the \$2\$ charges are ...
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derivative of current confusion

Say you have some B field from an alternating current, B(t)=B0cosωt. And using Faradays law, e.m.f. ε = turns of a coil × the time derivative of the flux of the B field going through the coil area. \$\...
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155 views

Electromagnet flux density calculation knowing specs of coil, core and applied voltage?

Seems to be almost a textbook task from a freshmen class. But I am truly puzzled. Electromagnet has a coil of tightly wound 100 turns of copper wire around a cylinder core with relative permeability ...
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Contradiction in solution for ideal transformer

I was trying to analyse an ideal transformer with one ideal independent voltage source on each winding. I got a relationship between those voltage sources but it contradicts the fact that both voltage ...
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195 views

How 3mG can be dangerous if the Earth's magnetic field is 500mG? [closed]

All the things I have read says that magnetic fields above 3milligauss is dangerous for people. How this can be true if the Earth has a magnetic field of 500mG? Do smartphones and gaussmeters measure ...
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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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How do I effectively trip a digital Hall effect sensor with low current. Magnetic field amplification?

This is part of a more complex project for school but here is what you need to know to help me. I have a DC voltage from 0-5 volts I must include a resistive load. The Hall effect sensor trips a ...
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122 views

What are the properties/advantages of concentric winding?

I have seen several 4 pole induction motors that have coils wound like this: Both the main winding and the auxiliary winding have 2 pairs of these coils. This is concentric winding and I've only ...
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What is the meaning of dBi?

When we say, for example, an antenna has spec of 22 dBi; Does it mean that its power is 22 dB stronger for any point at fixed direction than if it were to emit spherically?
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Losses over frequency for microstrip vs. coplanar waveguide

At mmwave frequencies, coplanar waveguide transmission lines generally have lower loss than microstrip. What accounts for this, besides radiated losses? Or is the difference mostly related to the ...
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163 views

Direction of current in a wire connecting two conducting loops placed concentrically in a time varying magnetic field which is into the plane of paper

Figure shown plane figure made of a conductor located in a magnetic field along the inward normal to the plane of the figure. The magnetic field starts increasing. What will be the direction of ...
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67 views

eddy current direction

As far as i understand eddy current direction is determined by lenz's law. But the following example - describes the currents and magnetic field direction when the current in the coil increases - ...
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1answer
64 views

Kirchoff's Laws and Maxwell Laws

If I want to use Kirchoff's Laws in a electrical circuit, I should assume that wavelength is greater than circuit dimensions. But this wavelength is from which wave? I know that it is related with ...
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CST waveguide port

I'm learning to use CST and I have a question about how waveguide ports work. From the official help I read that the software automatically applies to the edges of a waveguide port the same boundary ...
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257 views

Why are transformers cores made of iron and not nickel, when the relative permeability is higher for nickel?

Why are transformers cores made of iron and not nickel, when the relative permeability is higher for nickel? The permeability of nickel being 600 and the one of iron being 200.
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60 views

Floating Conductor Next to AC Power Source

Let's say I have a conductive metal sphere connected to a 50Hz 1kVrms AC Power Source referenced to Earth ground. About 3cm away, there's an identical metal sphere suspended by a non-conductive ...
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95 views

The results of my magnetic flux data from voltage recorded

For my electrical engineering senior design I created an experiment to test magnetic flux (more voltage) through a receiving coil. There is a large sending coil with A.C. voltage and a small receiving ...
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141 views

How to demonstrate mathematically the conditions of reflection in transmission line?

We are all taught about transmission lines and its associates -- characteristic impedance, reflection, standing wave, etc. It is well known what happens when a transmission line is terminated with ...
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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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94 views

Sinusoidally squeezing a capacitor

Assuming no load, how does continuously changing the distance between the plates of a capacitor (in a sinusoidal fashion for simplicity) affect the output voltage? Does electromagnetic induction come ...
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61 views

Mechanism of conversion of electrical energy to EM energy in LEDs

I've always been intrigued that electrical energy can just disappear out of a circuit 'into the aether' as RF. Of course thinking about it, some energy 'vanishes' as EM radiation even in a filament ...
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I bought an electro magnet and i have some questions

I've just bought a 12V 260mA electromagnet and I have some questions about it I don't know why, but when I connect electromagnet, my 12V power source (9V and 2 1.5V AA batteries in series) drops to ...
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43 views

Magnetoresistance from self current

I have done this question on physics forum but for some reason my question didn't receive any attention there(maybe because physics site is for theoretical physicists mostly) and I have this question. ...
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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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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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159 views

How can I generate a noisy environment to test my PCB?

I am developing a PCB project but i want to use the PCB in noisy environments (which usually contains 7.5-45 kW multiple motors with frequency inverters and also ignition transformers). I made some ...
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Finding EMF from the given graphs

Here are the graphs of flux vs angle and EMF vs angle. From it, I have to derive the following relation (expected answer) between EMF -Ui and change in flux with respect to time. My approach: I find ...
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4answers
174 views

How feasible is it to localize a robot based on EM beacon?

I am designing a little tabletop robot with a very simple goal of keeping track of where it is on the table as he traverses it. This, as it turns out, is a lot more difficult than I imagined. All the ...
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3answers
185 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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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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37 views

Transverse Flux Machine

For research, I want to build a levitation system that can levitate an aluminum sheet. With traditional 3 phase Induction engines you off course get levitation, but it isn't as stable as I want to. I'...
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191 views

Boundary condition for dielectric to dielectric

Now the tangential component of the electric field at the boundary is continuous, but the normal component of the electric field is said to be discontinuous. What is the meaning of discontinuous in ...
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42 views

Creating a 3 phase current

For an experiment (generating a travelling magnetic field) in high school I need a 3 phase current. My school does not have access to 3 phase power. Therefore I need to generate the 3 phase power out ...
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35 views

Traveling magnetic field

I'd like to do some experiments with a traveling magnetic field. To start with, I'd like to create a traveling magnetic field with a set of coils and try to propel an aluminum sheet. A basic model of ...
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37 views

Relay kept on by near transformer

I had a wireless powersocket for my PC peripherals until it stopped working. It just kept closed even if I turned it off and heard clicking. I opened the socket and replaced the board inside with my ...
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1answer
56 views

What external influences can a cardiac pacemaker have?

Since in these days there are lots of different devices and appliances which are sending out all kinds of waves or radiation and different strengths (e.g. RFID scanners, induction cookers, Bluetooth, ...
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184 views

Coil in magnetic field. Voltage step response

Say we have a coil in magnetic field as shown below (two empty squares are magnet poles). Now imagine we give some voltage pulse across the terminals. I wonder how would current (its magnitude and ...
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2answers
45 views

using solenoid magnetic field to press a button

I'm looking for a simple way to make Arduino press a spray button. I don't care which button to use, it can be either this type: or the following: I know there are ways to solve this problem using a ...
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89 views

Why do simple optical fibers usually support only half-duplex communication?

I'm a newbie to the subject, so a thorough answer would be very helpful. I was curious as to why simple (single) optical fibers usually don't allow full-duplex communication. To my understanding, all ...
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55 views

Ideal transformer primary and secondary inductance

It is said when current is circulating in the secondary of the transformer due to connected load, a flux is produced by the secondary current that is "seen" by the primary thus a current is ...
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1answer
71 views

Finding Potential Function

Till now I have derived potential equation like in the picture shown below. But now i stumbled upon derivation of potential for coaxial cable where the minus sign is not there in front of the ...
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2answers
194 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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1answer
68 views

H Field in a Rectangular Loop Carrying Constant Current

Question: A rectangular loop carrying 10A current placed on \$z=0\$ plane as shown in figure. Find \$\vec H\$ at i)\$(2,2,0)\$, ii)\$(4,2,0)\$, iii)\$(4,8,0)\$, iv)\$(0,0,2)\$. I just tried to draw ...
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144 views

Please help me solve the below Directional coupler problem

I have tried and my answer keep coming 0db.I am not sure this answer is right as this is only kind of problem I have seen where port is short circuited.
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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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69 views

how to understand unparalleled transmission line?

in a normal transmission line example, shown as case-1 in below picture, the signal path and return path are parallel to each other, let's say it takes 1ns for the signal propagate from left side to ...
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38 views

Why is my current measuring with the DRV425 wrong?

I want to get the current through a conductor by measuring the magnetic field of a conductor by using a DRV425. I use the DRV425 Evaluation Board with the original settings (...

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