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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16 views

How to calculate the pressure and velocity of an ionised gas that is being impelled with magnetic pressure

Calculating the velocity and pressure of an ionised gas based on magnetic pressure and magnetic force. Questions: Based on magnetic pressure expressed on an ionised gas, how do I calculate the ...
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62 views

Current source and electromagnetic interferance

I have a current source which has to be really precise in order to charge a capacitor and count a certain time (about 100 ms.) If anybody has seen a component which allows to count a time (without a ...
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Finding constant in electrostatic equation given only charge

So in a region of free space with zero charge, all I'm given is that the electrostatic potential V is given by: $$V(x,y,z) = kz(x^2) y + 2y - 6y(z^3)$$ [Volts] To find the constant k, would I have to ...
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55 views

Charging battery with a tiny coil and magnet

I am working on a chip design which will be used to track small fish (about 5 cm), so the chip has to be very small too. A big challenge is the energy supply. I will probably use a proven design for a ...
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52 views

Is there any risk if we stand in between two large conducting plates (capacitor) connected to supply?

What are the risks involved if one were to stand between two large conducting plates (i.e area where air acts as the dielectric for these plates) and the capacitor is connected to a large voltage ...
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62 views

Designing an electromagnet

I'm new to magnetics and apologize in advance if any of these questions are too basic. I'm looking to build an electromagnet array to move around an object placed on top of the array. Something ...
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27 views

What happens if you connect a “slant 45 radio unit” to a linear parabolic antenna?

If I understand it correctly the only difference between linear polarization and slant polarization is that slant polarization is just a 45-degree rotated version of linear polarization, and that ...
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3answers
70 views

How is torque proportional to current and magnetic flux in a DC motor?

It is well known in physics that a rigid body having a current \$i\$ in a closed loop under a magnetic field \$\vec{B}\$ experiences a torque which is \$\vec{T}= \vec{m}\times\vec{B}\$ where the ...
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86 views

Why is a microstrip line unbalanced?

It is known that a coaxial cable needs a balun to provide an optimal supply of a dipole antenna, because of the common mode current that comes back to the transmitter through the external surface of ...
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55 views

Are magnetic/electromagnetic damp proof courses a scam (active/passive EM Fields to stop capillary water wicking in stone) [closed]

At a home building show earlier this year, there was a company offering "magnetic damp proof course" which sounded a bit like snake oil to me. They pitch it as the next evolution of electro-...
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Negative sequence component rotation

I am reading some books trying to understand how physically they rotate in the same direction as the positive sequence components but in the reverse sequence. How can that even be. If a machine rotor ...
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52 views

Electrical conductivity circuit help, with two solenoids

I have a project im working on but cant seem to figure out the basic of the circuit. The principal of the circuit is two solenoids wrapped around a chemistry glass making a magnetic field. The purpose ...
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67 views

Why aren't magnetic substrates so used for RF printed circuits?

I've recently started working in microwave field, so I don't have big knowledge except for basic theory. What I've noticed is that, in rf and microwaves printed circuits (for instance for microstrip ...
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89 views

What is the meaning of Directivity and Reflection coefficient for a RX antenna? [closed]

it's known that the circuital models of TX and RX antennas are the following ones: They are fine, but I find it hard to understand the meaning of some concepts when applied at the RX case. For ...
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4answers
90 views

How to design a solenoid.?

I want to design a DC solenoid valve that could compress a spring under 5 kg of load. All I know is the voltage (12V), load (5kg), the current range (15-20), and the cross-sectional area of the ...
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56 views

What is the purpose of a superstrate above a printed antenna?

I've seen that there are some planar antennas which are not simply a metal patch above a substrate, but present also a dielectric superstrate. Some examples of this configurations are: This planar ...
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1answer
53 views

Powering a small generator with a contactless rotating plate

My goal is to contactlessly power a small generator by rotating a steel plate underneath it. Specifically, I have mounted 6 permanent magnets (rectangular shaped) on a shaft, which is mounted on ball ...
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58 views

Kirchhoff's law for magnetic circuit

I have been working on this problem: The way I approached this problem is given (I used Kirchhoff's laws on Electrical equivalent of magnetic circuit) : I have two doubts here: My working does not ...
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1answer
73 views

Diagram of electrostatic precipitator

I was reading an article about working of ESP at this website: https://www.electrical4u.com/electrostatic-precipitator/ Though the explanation was nice, I couldn't understand what the diagram conveys....
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413 views

Why is the voltage positive while the current is decreasing?

The question is: The solution is: The formula used is: So, based on the formula it should be like this: $$v_L(i)= L\frac{di_L}{dt}$$ $$v_L(i)= +0.4\frac{0.1-0.5}{0.01}$$ $$v_L(i)=-16V$$ Why did he ...
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8answers
5k views

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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1answer
34 views

Inductor/Electromagnet used to lift up a magnet? Joules to Newtons or Joules to Gauss?

With interest in using an electromagnet to lift up a magnet. I dove in. I will state general information. The set up is unknown but I'm interested in the physics/electrical engineering involved in ...
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1answer
73 views

Is it OK to allow to more than 16mA (say 1A) to flow through Raspberry Pi GND pin?

I am fairly new to electronics and I'm designing a circuit which has two electromagnets (in my diagram I've used bulb symbols as I couldn't figure out how to represent the resistance of the component ...
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27 views

Three-phase system with line-to-neutral voltage

I have the following problem: Consider a three-phase system with line-to-neutral voltage 268 / 0 ° V. It is Y-connected to a resistive load with ...
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2answers
58 views

Contour (curve) selection in the Ampere's circuital law

I need help understanding Ampere's circuital law. Consider a square shaped iron core with an N turn coil on one side. Let each side of the core has the length a an has equal cross-section. The ...
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1answer
35 views

Should the magnetic field outside a conductor be considered?

I've simulated a circular disc where a magnetic field is moving out of the page. The arrows in the picture represents the direction of its current density. I'm wondering, will the induced current ...
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2answers
109 views

Stray Voltage on Custom PCB

I've designed, ordered and assembled a PCB to act as an Arduino shield that takes sensor input and interfaces with a set of (again, custom design) motor driver cards. PCB images top and bottom ...
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3answers
105 views

Initial direction of a motor

When a motor is already rotating, the rotor's mass and velocity carries a momentum and will continue to rotate in one or the other direction to align to the stator's magnetic field as the polarity of ...
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How do i find the FNBW of a main lobe using a diagram?

Looking at the graph below, i can see that HPBW of the main lobe is around 45 degrees, but when it comes to identifying the FNBW i have trouble understanding it. Reading various articles online i've ...
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3answers
76 views

How does a wifi antenna work?

let's consider a common wifi antenna (used in routers) like this: I don't understand some its basic features: 1) Is it a dipole or monopole antenna? I see only one conductor, so I'd say it's a ...
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1answer
37 views

How to calculate the angle for the phasor form?

I have the following problem: A one-phase voltage of v(t) = 150⋅sin(wt)is connected to a load with impedance Z=2+4j Ohm. What ...
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1answer
80 views

How to write a voltage in phasor form (using a reference-voltage)

I have the following problem: Consider two voltages described by v1 = 325 sin(wt+10º) V v2 = 326 sin(wt+130º) V Write v2 in Phasor Form using v1 as reference... My Question is: I understand that the ...
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1answer
31 views

What's the logic inside the formula for the calculation of the maximal envelope modulation amplitude of two temporal interfering electric fields?

Since my question is a bit elaborate, I will first write some details. Thank you all! I refer to the study conducted by Nir Grossman et al. (2017) about the use of the temporal interfering stimulation ...
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1answer
62 views

Is a “magneto-dynamic” pickup possible?

I'm trying to imagine a fancy electronic circuit for an electric guitar with lots of customization options. Is it possible to design a guitar pickup analogous to an electro-dynamic speaker? Ie. using ...
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2answers
307 views

Transmission lines with same impedance but different dimensions

Suppose we connect two transmission lines with characteristic impedances \$Z_1\$ and \$Z_2\$. The reflection coefficient looking into the transmission line with impedance \$Z_2\$ is $$ \Gamma=\frac{...
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33 views

Why are fieldlines getting distorted near a conducting sphere?

Is the total flux of an electrical field through a conductor always zero because of Gauss`law? Does this cause the field lines to diverge, as they would offset the equilibrium? Quote from here: But, ...
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1answer
75 views

What is a unipolar inductor?

Can somebody explain to me, someone who has no idea of EE, what a unipolar inductor is? Im trying to understand the process by which the rotational energy of a black hole is converted into energy to ...
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1answer
60 views

A misunderstanding with Faraday's experiment with iron ring

I am learning about electricity and magnetism, and have got some misunderstanding about Faraday's experiments with iron ring. If iron can conduct electricity, why is electricity inducted only while ...
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1answer
31 views

Relationship Between Resistance and Magnet Strength for Electromagnets

I am working on a project using an electromagnet to vibrate the strings of a guitar at their resonant frequency. I have this working pretty well with an electromagnet I have on hand, I'm currently ...
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1answer
67 views

Do magnets interfere with my DC circuit?

I have a very simple electrical circuit that contains a 12V DC adapter, a 12V LED strip, and a switch. The catch is, that the LED's are controlled by a sliding door, which presses the switch and ...
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1answer
61 views

Electromagnetic coupling on printed circuit board traces

When I applied the following damped signal in the proximity of my product (the magnitude is around 10 kV and the frequency is around 400 kHz) through a cable of 4 meters, the microcontroller sees a ...
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1answer
60 views

How can a resonator do band-pass filtering?

I've read many times some statements about resonators like this (reference): Resonant circuits are circuits, which offers a high impedance or low impedance (for parallel and series resonance ...
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38 views

Oblique incidence over a stratified medium - the transfer matrix is not unitary?

As you've read on the title, my problem is about an oblique incidence problem over a stratified electrical medium. I've made a quick sketch with the incidence on the first layer. Let's suppose that I ...
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1answer
46 views

Multiple Resonances along a transmission line

in "Lessons in Electric Circuits", VOL III, ChPT 14, all the possible configurations of standing wave for a certain transmission line are shown. For instance, this is the case of a ...
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1answer
77 views

The coaxial cable is claimed to show the highest common inductance (M) relative to any other cable configuration?

The coaxial cable is claimed to show the highest common inductance (M) relative to any other cable configuration [Henry W. Ott, (1988), Noise Reduction Techniques in Electronic Systems, 2 Ed., AT&...
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35 views

How to apply Ampere's law with the integration path crossing a permanent magnet?

I read several books on permanent magnet synchronous machines (PMSM), and they tend to describe the relationship between H and B as \$B_{mag}=\mu_0\mu_{r,mag}H_{mag}+B_{rem}\$. Then when they apply ...
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1answer
82 views

Can we harvest energy from a Rogowski coil?

Can we harvest enough energy (4-5 watts of power) from a custom made Rogowski coil? The primary conductor is 33kV and has an average current of 10A. I'm aware of the induced voltage and the mutual ...
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44 views

Return path magnetic field on hall effect current sensor

We would like to use a toroid core and hall effect sensor shown in the figure below for measuring current in an Electric Vehicle from a battery pack. Questions are: Would placing the wire carrying ...
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3answers
298 views

Starting torque of series vs shunt DC motors

Recently, I read that starting torque of series motors are much higher than shunt motors. I try to find out what is reason behind it and I get to know that this is because in DC series motor torque is ...
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1answer
57 views

Confusion in magnetic neutral plane of DC machine

I was reading book Electric Machinery by Chapman and in topic 'Armature reaction ' It is written that "The magnetic neutral plane is defined as the plane within the machine where the velocity of ...

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