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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Why isn't there a potential difference across a disconnected diode?
I know this question sounds silly, as if there was a potential difference a current would be created when the terminals are connected together and this would mean energy has come from somewhere.
The ...
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How does the tester screwdriver work?
How does the tester screwdriver work? If I put the tester screwdriver inside the "hot wire" of an electrical socket, it lits up if I press my finger against the metal cap on top of the screwdriver. ...
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Stealing energy from radio towers or power lines
From this answer: How much energy can be harvested from nearby radio towers or power lines? What circuits would you use? How much would you have to absorb for it to be noticeable by the producers or ...
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Why aren't solenoid/electromagnet windings insulated?
This has been bugging me for a long time. Take this video for example.
I have always thought that electricity will take the shortest path. When the electromagnet's windings are uninsulated, it seems ...
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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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How fast does electricity flow?
I get confused on the low-level physics of electricity from time to time. It came up in "Which way does electricity power a circuit," and I don't totally get it.
How fast does electricity flow? Is ...
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Transient analysis of inductor circuit and back EMF
In a lecture exercise from a circuit course, I encountered the following circuit with only an inductor and a voltage source. The \$v\$ vs \$t\$ and \$i\$ vs \$t\$ graph is as follows:
-The KVL ...
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Why is flyback air gap needed for energy storage?
Why do so many sources say something along the lines "since a flyback transformer stores energy, an air gap is needed"? I have seen this reasoning in textbooks and app notes.
I thought air gaps ...
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Why doesn't an AC solenoid coil change magnetic polarity on each cycle?
I am trying to figure out how an AC solenoid coil maintains its N and S magnetic polarity.
Since in a sinusoidal AC, current alternates in both directions. How does the solenoid not change polarity (N ...
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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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Magnetic field strength and flux density from hysteresis curve
I am trying to measure the magnetic hysteresis curve of a toroidal nanocrystalline ferromagnetic transformer core made of Nanoperm (datasheet linked) using the following circuit. Each of the windings ...
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Powerful electromagnet?
Is it possible to produce over 1000 lb of magnetic force over a distance of 4 inches(0.101 meters), using an electromagnet?
How difficult would it be? Explaining the general spec's of such an ...
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emi standards/best practices for PC cases
According to an EE friend, the FCC specifies EMI tolerances (max outputs) for PC components, including cases. However, here it says that there are standards for a number of components but not cases.
...
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Does Shielding "Electrically" shield "Magnetically" too?
I know it sounds like a newbie question but I can't wrap my mind around it. An electromagnetic field is electric + magnetic field.
So this means that when shielding an equipment offensively, for ...
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How does a transformer transmit power from the primary to the secondary?
I'm trying to get my head wrapped around transformer operation and in the process regretting the times I snoozed in my Electromagnetics class as a EE student back when I was a lad :)
I'm looking for ...
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What are the bare minimum parts needed to operate a magnetron?
I recently took apart a microwave, and I managed to get a magnetron out of it, as well as a transformer that appears to be the power source for the magnetron, but looks a little small for the ...
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Open Source or free electric field mapping software
Looking for recommendations for 2D (or 3D) electric field mapping software. I want to be able to populate a series of electrodes in a plane and understand the equipotentials present when these ...
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How much power is radiated by cell towers?
I want to know how much power is radiated by cell towers of GSM (1.8 GHz), 3G (2.1 GHz), 4G (2.6 GHz.)
I want links to references if possible.
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Current waveform in an inductor with AC source
If we connect an AC source with a pure inductor when AC source is going through 0 volts we get the following graph of the voltage and current.
There are few things in the graph about which i am ...
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Inductance of a practical relay
I would like to design an SMPS to feed an electronic circuit that includes a relay. To study the stability of my SMSP I need to model the relay, but when I go through many relays datasheets, they do ...
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How do skin-effect and proximity-effect behave for flat-conductor power inductors?
Here is a Digikey search showing flat-conductor power inductors.
And here is a picture of three power inductors found there:
In this answer, by Rohat Kılıç, towards the end of his answer he explains ...
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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. All ...
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Are E and B fields in phase in electromagnetic radiation?
I recently wrote this answer, in which I said:
Radio waves are electromagnetic radiation. Electromagnetic radiation contains of two components, one electrical and one magnetic. These components ...
user17592
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Is it valid to consider back-EMF in a DC motor equivalent to increased inductance?
I know that back-EMF can be considered as a voltage source in series with the motor which is proportional to speed. This is the common understanding, and I totally get it. Before I understood this, I ...
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Circuit yields a peculiar contradiction between KCL, KVL and Faraday's law
I don't know if this particular circuit/loop is covered in another question but I stumbled upon a video where a peculiar consequence occurs for the following circuit:
For the above circuit loop ...
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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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Intuitive explanation of Skin Effect?
I'm trying to wrap my head round Skin Depth, we've derived the wave equation from Maxwell's equations, using the conditions that it's a "good conductor" ρ = 0, σ >> ωε and ...
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Homebuilt magnetic tape head
I have seen a lot of projects that use a tape head, but there is very less information about how to build one yourself. Is this possible?
I know that basically it is a metal core, with a coil around ...
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AC solenoid valve with DC
I have a 24VAC/60Hz solenoid. I used 12VDC just to try, and it worked good (well needless to say it worked as expected with 24VAC/60Hz).
What are the effects of a solenoid that's designed for AC ...
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Transmission Line Effects
My question has to do with the rule of thumb we generally use when dealing with transmission lines.
We say that if the length of the line is 10% or less of the wavelength, we could neglect the ...
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Does electricity flow in open circuits?
Say I have an open circuit with a battery. I have a wire connected to the negative terminal and a wire connected to the positive terminal. The wires aren't connected.
In this scenario, would their be ...
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Why don't my coil work?
I disassembled my old Niko RC car today. Thought I could play around with the parts.
But what I can't seem to understand is the coil. The powersource of the rc car is a 7.2v NiCd 620mAh battery. And ...
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Advantages of parallel over serial connections
As far as my understanding goes, parallel data connections are faster than serial at the same frequency. However, when you increase the frequency in parallel you start getting bits 'cross-talking' and ...
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Coaxial Cable vs Shunt, path of least impedance
The website LearnEMC.com has a page called Identifying Current Paths which contains the following graphics.
The graphic on the left shows a coaxial cable arranged in a "U" shape, with a ...
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Magnetron Working Principle
I was reading this simple description of magnetron working principle.
Can you explain me why when electrons go near the cavities, they start to resonate at microwave frequency? I do not see the link ...
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Electromagnetic Energy Harvester
It was suggested I make a new post since the topic was growing in complexity.
I am looking into constructing an inductor to utilize electromagnetic induction near a high voltage transmission line. If ...
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Good resources/books for electromagnetics and other advanced concepts
I'm looking for some good resource that teaches the fundamental concepts behind electronics. I'm not looking for a beginner book. I'm already in the final year of my Electronics and Telecommunication ...
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3
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Electromagnetic charging
I'm building a circuit that uses a really low voltage and current. I thought that instead of using a standard battery it would be nice if I could use a rechargeable battery and charge it with ...
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Reflection coefficient of a transmission line with discontinuity
I have a question, let's say that we want to calculate the Reflection Coefficient that we see by watching from left to right of the red-line this circuit:
Let's say that:
Za= Equivalent Impedence of ...
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How to determine the correct graph for induced current
To be straight , this is a home - work question .
This is the question.
Okay, now let me give you the my attempt and what I believe to be correct.
Here E.M.F induced across OA is constant, ...
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Why don't electrons get repelled by the negative side of the the voltage drop across a resistor? [closed]
We can clearly see that the electrons are moving from negative side of the voltage drop across the resistor but why are not they repelled by that side?
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Cable type and decreasing EMI/RFI
I am interested which cable/wire type is better to protect against electromagnetic and radio interference/leakage of signal.
Is a twisted pair wire better than an untwisted, to protect against EMI/...
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What is the speed of "electricity"?
In a distribution grid, what is the speed of
energy
signal
Is it strictly the same?
And how is synchronisation achieved? Is an electric grid essentially an orchestra where everyone is the chief ...
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Help with homemade electromagnet
Just for fun, I decided to build what I was hoping would be a relatively powerful electromagnet. I used this copper wire (20 AWG, entire 1 pound spool) and this soft iron core (0.5 in diameter, 6 in ...
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How does a Theremin "antenna" work?
I always assumed that the shape of the antennas was important; a vertical monopole for pitch and a horizontal loop for volume, thinking that this minimized their interference with each other. But it ...
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How does this iPhone app measure the power flowing through an AC appliance cord?
My electric utility released an iPhone app called "DTE Insight" which (among other things) measures the amount of power flowing through an appliance's power cord by asking you to hold the cord against ...
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How to properly wind coils for a solenoid?
I need to wind a small electromagnet "solenoid?". About 3cm high and 2~5cm wide running at 5V/0.5A. This magnet will be put into a desk bell so it pulls the clapper down and rings the bell. I have ...
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What is the difference between electromagnetism and electromagnetic radiation?
In a previous question, I asked if having 2 coils of wire with electricity flowing from one to the other is RF, and they replied that it was not Radio Frequency. I was puzzled because I thought this ...
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How does a gold leaf electroscope measure voltage?
It’s my understanding this device can be used to measure voltage. How is this accomplished? What electromagnetic equations are applied and how is it calibrated?
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Controlling an electromagnet strengh with arduino
This previous question Controlling an electromagnet with Arduino deals with binary control (ON or OFF) only.
On my side I need to choose the strength of the magnetic field.
It is a home made ...
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