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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187 views

Mixing wavelengths to produce light? [closed]

It's a mixed part question: 1) Is there any way to add 2 wavelengths outside of the visible spectrum to create a wavelength in the visible spectrum? 2) If this is possible, would those wavelengths be ...
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3answers
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Controlling Electromagnet Via USB

I need to control an electromagnet via USB with an android phone, to make a small educational project. I know how to write the software, but how can I control an electromagnet via USB? Via an USB ...
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Do diamagnetic material exhibit induction?

Silly question perhaps, but do metals with the property of diamagnetism also exhibit inductance? Would a fluctuating magnetic field induce a current in a diamagnetic metal?
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Do electromagnetic shielding stickers do anything?

I recently bought some cellphone accessories, and as a free gift, the merchant gave me a "24K gold plating electromagnetic shielding sticker", whose instructions are all in Chinese, but I guess you're ...
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1answer
450 views

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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3answers
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Can the coil in a magnetic field be replaced by a copper mesh?

From theory, I remember that EMF induced is a function of the rate of change of magnetic flux. A generator is typically a changing magnetic field applied to a bunch of diamagnetic wires wound closely ...
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4answers
589 views

Will a faster rate of change of flux improve electricity generation?

From what I remember about electricity generation, a varying magnetic field is used, either the magnetic field or the coil moves to generate electricity. e = dB/dT where e = voltage induced B = ...
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2answers
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Generating Strong Electric Fields

What is the best way of generating strong, steady, electric fields (E) using the tools and voltages available to the home hobbyist? Is it better to using electrostatic sources like a Van de Graaff ...
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4answers
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Is it possible to record a range of radio frequencies in one go?

I am wondering if the following is theoretically possible: The device can record say 1 hour of electromagnetic wave/radio signals today, and in the future recreate/replay that, so people can listen ...
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1answer
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What use is the copper foil between the primary and secondary windings of a transformer?

I took apart a small transformer. It is of shell construction type. Beneath the primary windings, I found a strip of (floating) copper foil wrapped around the secondary windings. Of course there is ...
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3answers
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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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2answers
359 views

Electromagnet force

If connect a battery to an electromagnet, would the magnetic force be equal stronger or weaker if I used a battery with a capacity of 5000V and 0.5A (2500Watt) or 0.5V and 5000A? Or will it be ...
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Why do we need brushed motors?

Looks like brushless motors are more convenient - no brushes means no maintenance required. For example, power tools manufacturers often cite that graphite brushes need to be replaced every 50 hours ...
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9answers
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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 ...
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1answer
607 views

Should I avoid placing a SMPS inductor close to a magnetometer?

I am designing a board, which has a high current (~2A) buck-topology switch mode power supply on it, which uses an unshielded SDR0805 inductor. About 4cm from it, there is a magnetometer (combined mag/...
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1answer
850 views

Safely connecting an solenoid/electromagnet to a switch-mode supply

I'm currently working on a project that involves hooking up an arduino, a cellular shield, and an electromagnet (in this case, one of those old fashioned ringer boxes with a bell powered by ...
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3answers
1k views

How to build a constant magnetic field source for a “railgun”?

I'm trying to build a device similar to railgun. It will have two rails and a conductive movable bar in-between. At one side, I'll provide voltage source and a resistor. If I put it in a strong enough ...
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3answers
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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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2answers
2k views

DC motor Armature and Field back emf

In a motor where both the field and armature are wound there are at least two possible control scenarios. The field winding can be excited with constant current and the armature voltage controlled, ...
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3answers
639 views

Controlling a mechanical shutter with an electromagnet

I'd like to drive a pair of mechanical shutter / apertures with an electromagnet. For those curious, we're using a shutter from Edmond optical. For the particular application, I'd like to design a ...
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3answers
23k views

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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1answer
295 views

Small displacement measurement of a conducting beam with Neodymium magnets

I relies the displacement is very small and with up to a decent frequency. Here is details of the Magnet data Magnet poles North/South over the height(h) = 1.5 mm Coating: Nickel Length(a) = 8.5 mm ...
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6answers
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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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2answers
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When do non-TEM waves occur?

Yesterday, I read about TEM waves on wikipedia. Those are waves that have no electric or magnetic field vectors pointing into propagation direction of the wave. But on any picture illustrating EM ...
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Electromagnet design

Im trying to design a maximum strength electromagnet. I have a soft iron core that is 1.3" (33mm) round by 1.9" (50mm) long and I'm using 12 volts of input and my wire gauge is 18awg. Unfortunately I ...
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2answers
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Can a magnet be an antenna?

I have a project for a small remote control in which I'll use a magnet instead of screws/etc. to close the case. Basically it is a two-piece plastic case in which one of the pieces has a magnet glued ...
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5answers
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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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1answer
610 views

Driving an electromagnet with a 556 timer

I'm trying to drive an electromagnet with a 556 timer in a push pull configuration. The magnet has to change polarity rather quickly and sharply about 10 to 20khz. The voltage also has to be variable, ...
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4answers
618 views

Amplifying instruments by measuring current in conductive strings

The normal musical instrument pickup uses a magnet inside a coil, and the movement of a ferromagnetic string causes changes in the magnetic field, which then induce currents in the coil. Another ...
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8answers
768 views

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 ...

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