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 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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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 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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What is the difference between the magnetic H field and the B field?
Wikipedia provides a mathematical explanation. Can I get the intuitive one? I'd like to, for example, understand a ferrite datasheet. These usually have graphs of H vs B, and the definition of ...
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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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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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Is it possible to generate light with an antenna?
An antenna (e.g. a dipole) is able to radiate at a certain frequency thanks to the EM field generated by a current provided by a signal generator at such a frequency.
So, for instance:
Voltage source ...
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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 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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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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In which direction do electric signals flow?
We know that electrons move from the negative to positive terminal, and that holes flow in the conventional direction of current - from the positive to negative terminal.
I've always assumed that this ...
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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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Why does a simple conductor start to emit EM waves when carrying a signal?
I understand that on circuit board traces with a clock, if the higher harmonics have sufficient power, it results in electromagnetic waves being emitted from the traces which creates EMI. What I don't ...
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Why does the thickness of a wire affect resistance?
A teacher explained why by using a highway analogy. The more lanes you have, the faster the cars go through, where the number of lanes obviously represent the wire thickness and the cars represent ...
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Can antennas be viewed as light sources?
Clearly antennas are nothing but a device to radiate the electrical energy through electromagnetic waves.
Since visible light is also simply a certain range of frequencies, isn't it more easier to ...
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Why does magnet wire need to be insulated?
What is it about having multiple coils that enables the magnetic field? Why can't I just have one big wire or threaded wire on a motor? Sorry, it's kind of a baby question but I couldn't find the ...
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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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In a DC motor, is there one commutation point that is optimal in all respects?
This recent question got me thinking about commutation timing, and why advancing it can be desirable. However, I wanted to consider more deeply the underlying phenomena, and I'm pretty sure my ...
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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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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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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 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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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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If electrons move slowly in an electrical circuit then what signal or energy is it that travels at the speed of light? [duplicate]
I am reading "Radio Theory Handbook" and am confused with the statement that says that electrons are moving through the wire at snails pace.But it goes on to say the "electrical effect" is ...
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Why does this metallic magnetic core have so little core losses up until 100s of kHz?
I have a small signal transformer with values as in the below schematic (the simulate button works well to see the AC response). The values are measured and the simulated AC response agrees sort of ...
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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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How to shield microcontroller from electromagnetic interference
I'm working with high voltage circuit (2.1 kV for defibrillator capacitor testing) and I'm controlling power supply with arduino, reading required information from laptop using serial interface. Most ...
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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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What is the physical significance of the unit ampere/meter in magnetics?
I'm having a hard time understanding what is the stuff this unit measures. I understand ampere, and I understand meter, and I understand per, but since ampere is a measure of current, I'm having ...
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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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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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How does a guitar body affect electromagnetic pickups?
If the pickups are just electromagnets detecting vibrations in metal strings, what effect does the guitar (size, shape, type of wood, solid body, hollow body) have on the pickups?
Most argue that the ...
user4345
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Construction for a homogeneous field using permanent magnets
Please let me describe what I am trying to achieve and I will pose my question in the end.
I am trying to design a small chamber which can have a uniform magnetic field inside. I want to see if a ...
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Can a credit card be demagnetized with a nearby cellphone?
Suppose I have a standard credit card with a magnetic stripe, lying
right on top of a cellphone, or
in a regular leather wallet that's lying right on top of a cellphone.
The cellphone is on (but ...
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Parallel decoupling capacitors: Is inductance reduced?
Background
In general, when placing decoupling capacitors in parallel, their capacitances add and their compound ESR is reduced (like for parallel resistors). But I am a bit uncertain if/how this ...
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My "nail and wire" electromagnet isn’t working
I’m trying to teach myself electrical engineering. I am trying to make an electromagnet using a 9V battery, alligator clips, and a steel bolt.
Steps ->
Wrap wire
Connect power
I have no ...
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answers
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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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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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How does a "coilgun" work?
I was wondering how that so-called "coilgun" works, I know what it does but I was wondering how it works under-the-hood and eventually how to make a basic one ? Also, how much energy would be required ...
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Using the audio input port as a voltmeter
I'm a physics undergraduate currently studying electromagnetism. I have no experience at all with playing with electronics. I'm trying to see the effect of a changing magnetic field on a closed ...
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Constant current in a circuit?
simulate this circuit – Schematic created using CircuitLab
A battery pumps electrons by creating an electric field and converting electric potential energy to kinetic. Near the positive ...
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Does heat affect the magnetic field of an electromagnet?
I know that heat destroys perm magnets, but how about electromagnetics? Does heat affect the strength of an electromagnetic field?
user3045
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What is the dielectric constant of a fly?
Kind of a random question, It has been a topic of debate in my lab. I guess the more specific question is: what materials is a fly's body made out of, and what are their dielectric properties?
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Digital Signal Cables Penetrating a RF Shielded Room
Disclaimer: I'm not a trained electrical engineer...I'm a recent Computer Science grad with about ten years experience as a RF test tech. I don't know everything, and to me, experience reigns supreme ...
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Does a radio station main amplifier work at the speed of light?
I'm having an argument with a classmate and we can't agree.
He tells me that it's not possible for the amplifier of a radio station to amplify the input signal "instantaneously" (at the speed of ...
Alexa
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How do I build an electromagnet?
I want to make an electromagnet that can lift a paper clip off of the ground from a short distance (probably 7 to 8 inches). I naively thought of making an electromagnet as a simple task (because of ...
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Inductors & magnet - no vibration
I was trying to make a device which can vibrate - so I took inductor, some 220uH 22uH, put 12V pulsed current through it (~10Hz), and put neodymium magnet - I was expecting to feel 10Hz vibration of a ...
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Why are vacuum tubes more resistant to electromagnetic pulses than solid-state devices?
I heard that equipment that uses vacuum tubes are generally less susceptible to electromagnetic pulses than those that employ solid-state devices.
I don't know if its true, because I didn't find any ...
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How to reverse rotation direction of stepper motor
Is it possible to reverse a stepper motor's direction of rotation by changing the polarities of its wires?
I'm asking because I have two stepper motors connected to one single driver and mounted on ...
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