# Questions tagged [electromagnetic]

Electromagnetism, or the electromagnetic force is one of the four fundamental interactions in nature. This force is described by electromagnetic fields, and has innumerable physical instances including the interaction of electrically charged particles and the interaction of uncharged magnetic force fields with electrical conductors.

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### Tesla AC motor: operational question with field direction

I have a question on the direction of the magnetic field for each of the four windings of the pictured AC motor. I ask because the wires are not clearly labeled as to direction of each winding, in ...
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### Flyback leakage inductance effect

The document "Under the Hood of Flyback SMPS Designs", talks about the leakage inductance effect (on page 6). I have some questions about that. The below questions are from fig 5. Why high ...
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### Do high voltage modules produce electromagnetic waves?

I have been experimenting with one of these 3-6V high voltage modules: I know the specifics of how they work, although I have recently been wondering about something. In a video by ElectroBOOM, he ...
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### How can I set the peak voltage in an AC waveform?

I am trying to make a small generator, nothing fancy just a coil of wire, and I was curious as to how the peak voltage of the waveform could be changed. Is the only way to increase this voltage with a ...
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### Does a receiving antenna radiate the power received?

Let's consider the case of linear dipole antenna or Hertz dipole. I know that the antenna acts as a transducer and it radiates the E-M waves due to the acceleration and decelaration of the electrons ...
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### How does balancing currents within a cable or conduit cancel its magnetic fields?

I know the NEC requires all current carrying conductors of the same circuit to be included in the same cable or conduit [300.3(B)], but why? I think it is because the magnetic field generated by ...
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### Stacked solenoids - wire in series or parallel for strongest pull?

I have three coils, each 25mm long, which I have bolted together in a stack. I wish to use this to pull in a moving soft-iron core, which will need to be pulled in nearly the full 75mm. Each coil ...
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### Could the electromagnetic field (EMF) from a power station disrupt wireless signals?

I know that power stations can generate an electromagnetic field, but is that field strong enough to disrupt nearby wireless signals, such as Wi-Fi, Bluetooth, cell service, etc? I'm sure that, in ...
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### DC Vacuum Contactor Coil - Failed Close

I am using a 350A DC, normally open vacuum contactor that experiences a failure while the contactor is closed (coil energized by 24VDC) for an industrial 1000VDC application. The manifests as the ...
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### Real life example of lossy medium

I’m learning about electromagnetic fields in class and a real life example of lossy medium would be helpful. I also don’t know how intrinsic impedance connect connects to lossy medium - probably ...
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### Magnetic field shielding for electronics?

I am looking at an issue where a PCB design that is powered by a couple of CR2032 batteries will shut off all of a sudden in the presence of strong magnetic fields (around 15-40mT). However, when the ...
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### Why do we need to install a variable frequency drive to reduce the energy consumption of a motor?

I have read that the power consumed by a motor under various load conditions is not constant according to the answers to this question. The electrical energy input changes according to the torque ...
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### Confused about back EMF protection in maglock circuit

Straight upfront...electrical engineering is not my forte. However, I am trying to help a client with a particular issue and I'm hoping this community can provide some invaluable insight. They have a ...
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### H-Bridge with highly inductive load

I am trying to understand the H-bridge, I have edited the circuit and followed the advice in this thread. Is this a good H-bridge design for excitation of the magnetic core which is highly inductive ...
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### What energy/fields if any is generated when radio frequency is passed through a coaxial cable?

I am new here. Just had a question wondering if someone could answer. Let's say I have a generator that can generate RF and send it through a cable (coaxial) if I attached the end of that wire to a ...
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### Temperature measurement in strong AC magnetic field

I have a coil that is continously driven with a maximum of 100A RMS of current at a frequency of 20kHz. The coil is water-cooled and I would like to directly monitor its temperature. The temperature ...
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### Can an electromagnet be made from copper tape?

Can a roll of copper tape act like a solenoid when connected to electricity? How does it compare to a solenoid of the same size made from copper wire?
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### Does acceleration come from a change in current?

I have a current connected to a wire and let's say when we measure the current at a particular time it reads differently than it does after some time. Does this imply the current is AC? I'm asking ...
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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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### Multiple questions about magnetic levitation including modelling and how to achieve it

I have several questions regarding magnetic levitation. If I have missed something in one of these questions then please do let me know. I am working on a magnetic levitation project using an Arduino ...
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### Determining the type of magnet used in a hand-crank torchlight

I'm trying to design a DIY dynamo that recharges a 5V battery used to power some sensors. However, I am having some trouble with deciding on the arrangement of coils and magnets. Currently, I am ...
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### How to Limit Current Using L293D?

I’m designing a circuit to control 4 electromagnetic coils and subsequent orientation of a sphere (pic attached below). I’m new to EE but thanks to this forum I’ve learned what and how to utilize PWM ...
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### Can I use PWM to lower the supply to an EM brake

I am working on a board that is supplied from 48v battery. the design contains multiple dc/dc converters (5v,3.3v). one the functions of this design is to control an Electromagnetic brake (24v 1A up ...
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### Possibility of achieving magnetic levitation(Arduino) with just one solenoid and a ring magnet?

I am currently working on a magnetic levitation project and have been looking into all types of magnetic levitation. One particular video I found around the subject was this: https://www.youtube.com/...
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### Calculating number of turns an electromagnet has

The title, but can one calculate the amount of turns on a coil or find that out somehow? Because I purchased a 120m copper coil (originally intended on using it on another coil former before giving up ...
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### Estimate electromagnetic emission due to current in wire

I am working on a project that will need to pass CEM requirements. I would like to "estimate", as in, get an order of magnitude of the electromagnetic emission. The device include 2 parts. ...
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### How do I make an electromagnet that weighs less than 2 kg but can exert a force of at least 420 N

For a project that I am doing currently I will need an electromagnet whose total weight is less than 2kg, but can exert a force of at least 420 N on a ferromagnetic material 0.03 m (3 cm) away from ...
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### Do high impedance nodes have higher noise due to inductive coupling as well?

This link clearly explains how high impedance nodes are susceptible to capacitive coupling noise. Is the same true for inductive coupling? As per my understanding, inductive coupling would induce an ...
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### Why is the linear phased array pattern a sinc (visual interpretation)?

It has for sure a very obvious answer, but I must admit I find it very difficult to visualize how a linear phased array can focus the beam with a sinc pattern. I'm not talking about the mathematical ...
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### Amplifier with bipolar transistor

What does input and output impedance (I/O) in electronics mean? This is in my book but I didn't understand it. Please explain it to me
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### EM radiation hitting atoms [closed]

What happens when the EM wave is incident on a atom? Do the de-localized electrons in the atoms or the valence band electons move in the direction of the electric field? Also when the electrons move, ...
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### Electromagnetic radiation diagram

Would I be correct to assume that this diagram isn't really how the field propagates in space? But it's just an illustration of the changing electric field strength as a function of time? For example ...
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### Near Field from a Dipole Antenna

What are the equations defining the near field of a half-wave dipole antenna? What is the rate of decay of E-field and H-field in the near field (both reactive and radiative zones)? How are the ...
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### Audio Engineer needed to read 14-track magnetic tape

I have a 20 mm magnetic tape, with 14 channels. The data tape does not have any sound and format in which data has been stored on tracks is as follows. The picture of tape head is as follows. The ...
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### Is Ohm's law valid in AC circuits?

I am confused over this and I’m hoping for clarification. By Ohm's law we can compute the resistance of a circuit as V/I. In the case of two sinusoids we have sin(x) / cos(x) or something like that. ...
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### Coil generator in practice

I am trying to create something like gyroball. Which features LED lights, so the faster the spinning, the more light LEDs emit. This seems like a simple scenario of a coil generator. As an experiment, ...
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### Total force made by the magnetic fields and the current, it should be zero but as I tried to derive it , the upward components only remains

As shown in the above diagram , the same 2 coils of square are aligined with paralell of same plane . $$I:=\text{current which flows to each wire of the square }$$ What I am confusing to ...
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### What is the difference between applied voltage and induced voltage at primary side of transformer specifically?

I am not able to understand difference between applied voltage and induced voltage. Whenever voltage is applied at primary side of transformer there will be primary current producing flux using ...
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### Derivation of microscopic Ohm's law from macroscopic version?

What I tried was: $$\overrightarrow{E}= - \triangledown V \qquad \qquad\qquad\qquad (1)$$ $$V= IR\qquad \qquad\qquad\qquad\text{(Ohm's law for materials where V}\propto \text{I)}$$ \text{...
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### EMC/EMI tests should be applied to power transformers or not?

I'm currently working in a naval industry. I see that EMC/EMI tests aren't applied to many of the transformers in combat ships. I wonder, is there any logical reason or explanation for this? I also ...
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### How to plot graph of perpendicularly polarized uniform plane wave is incident obliquely on a dielectric to conductor boundary using Matlab

I am writing the code for the equation which is attached below ( image of equation). I have written the code but getting errors. I want to plot the graph of E and H as underlined in the image. In the ...
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### How to apply traditional boundary conditions in A-V formulation for EM computation

I am using finite element methods for solving Maxwell equations based on A-V formulation with Lorenz gauge. Here A denotes the magnetic vector potential and V denotes the electrical potential. However,...
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### Inrush current and locked rotor current

The way I understand it is as follows: Inrush current is the high current drawn by a motor during its acceleration period. Inrush current begins when the motor is turned on and continues until it ...
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### How can Bluetooth, WiFi, ZigBee use the same frequencies but have different area coverage?

What makes radio frequency spectrum cover a larger distance for data transfer? Bluetooth, WiFi and ZigBee all use the same band (2.4 to 2.5 GHz) but their coverage area is different. Why? If it's ...
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### Capacitance of current carrying wires (Transmission Line)

Let me explain my primitive understanding of a capacitor. In electrostatics, a conductor containing accumulated charges attracts opposite charges in a conductor that's separated by an insulator, this ...
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### How to compute electric field between constantly changing potentials (LFP data)

I have a set of LFP (local field potential) data, which is basically the voltage of different points in the brain at different times. I would like to calculate the electric field at these points at ...
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### I need an explanation for the dereviation of a factor in the Two-Ray Model in Wikipedia

In the Two-Ray model, I wish to understand how the marked factor in the attached picture has been derived. source: https://en.wikipedia.org/wiki/Two-ray_ground-reflection_model Is this factor the E ...
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### What direction of force on the conductor in a magnetic field?

The question: The answer: In my opinion the force should be UP! Source: PPI PE Power Practice Problems, 4th Edition – Over 400 Electrical Engineering Practice Problems for the NCEES PE Electrical ...
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### How to manipulate a PIR sensor?

The passive infrared (PIR) motion sensor detects movement of infrared light sources with wavelengths ranging from 7 μm to 14 μm. Is there a way to make it detect below 10μm or to make it detect ...
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### Relay sepcs and Contact capacity explain

I design a simple control system using MCU, ECU and a relay to control an 220vac inductive load of 20A max current So i decided to use a 30A relay I found two relays JQX-16F(T91) - write on them the ...