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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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Would a pure homopolar motor be possible by using a partially twisted pair wire?

For the past few days I have been working on a conceptual design of a pure homopolar motor and I am at a point in which I would like someone to verify if I am correct concerning a key design issue. I ...
WaterSparkle351's user avatar
1 vote
1 answer
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Core memory output line question

How is a bit read from the core memory pictured below? I understand current through 1 and 1 vs 0 and 0 will change the torus magnets field setting a bit. I’m confused how this field is read back using ...
notaorb's user avatar
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Calculate alternator power from open voltage and short current

A 3-phase BLDC motor, used as an alternator, outputs 3V open-circuit and 5A short-circuit at a given RPM. How can you calculate or at least estimate its useful power at that RPM if we connect it to a ...
ololo ololo's user avatar
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Why mutual inductance be less than or equal to geometric mean of self inductances of coils?

I understand when coils are coupled together the leakage of flux into surroundings causes mutual inductance to be less than self ones but why it has to be less than or equal to geometric mean of the ...
Hafsa Mahmood's user avatar
1 vote
1 answer
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Is there a simple approximation for B-field strength of a loop antenna when driven at 10 GHz?

I have a near-field loop antenna that I'm applying a microwave field to at 10 GHz. I'd like to have it interact with a small magnet that is much smaller than the loop. Here's a picture with the little ...
Steven Sagona's user avatar
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1 answer
57 views

Injecting bits to a parallel communication bus possible?

Antennas can recieve data (bits) because RF signals induce an analog signal into it in a serial format, essentially a voltage that varies over time. My question is can we have an antenna that can ...
19216811's user avatar
1 vote
1 answer
34 views

Should I replace my stepper driver since my motor is acting up?

I've been using a Pancake Bipolar Stepper Motor for a project and STSPIN220 as the driver, but I've been randomly having a lot of current issues causing my motor to jitter. My project has been running ...
alxzhu's user avatar
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Numerical calculation of the Electric field in a system knowing the potentials on the contour

I have a problem in numerically determining the electric field lines given the potential in a system described in the photo. The electric field vector E is related to the potential at a point with the ...
Franc's user avatar
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How to predict the efficiency of a very low speed Railgun Actuator/Lorentz Force Actuator?

Well, I read somewhere that the slower the railgun is, the higher its efficiency, so I started trying to find out what would be the efficiency of a railgun actuator to move a heavy object (3000kg) at ...
Fulano's user avatar
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2 votes
2 answers
580 views

If electromagnetic waves are indeed created by a changing electric and magnetic field, then why don't we see magnet based antennas?

I understand that exciting electrons, basically freely moving electrons cause electromagnetic waves. The faster they accelerate the higher the frequency of the waves. If this is indeed the case, then ...
Vishwa Mithra Tatta's user avatar
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What parameters give unlinear torque model of induction motor?

I want to realize factors which give nonlinear model of torque toward speed with power consumption in induction motor. I tried find math model induction motor. But usually, I had same charts: As we ...
Alex F's user avatar
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1 answer
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Polarization Derivation

Can how I can find the phi and theta unit vectors as described (Eq. 4a and 4b) in the following paper on antenna cross polarization? I thought the thetha and phi unit vectors were the same as those of ...
DTBolt's user avatar
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2 votes
0 answers
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Electron beam welding light arcs and insufficient vacuum [closed]

I have an electron beam apparatus in a small vacuum chamber. When powering the holder and grid cap to high voltages somewhere between 1-10kV while the filament is heated, the following visually ...
Magemathician's user avatar
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1 answer
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FE Practice Question: How to use the given formula?

For this problem, the answer states to use the given formula. However, I'm not sure how to use it as it involves solving the square root of a complex number. Additionally, I'm not quite sure how the ...
Andrew Wong's user avatar
2 votes
1 answer
74 views

E-Core Electromagnet Vs. Bar Electromagnet: Force and Range

I have this microwave transformer (model number MD-601AMR-1) that I repurposed into an electromagnet. And it is very strong, but the magnetic field does not reach out far enough for my application. ...
Ombrezz's user avatar
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1 answer
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What makes a round axle spin in a rotating magnetic field?

Consider a round electromagnetically featureless axle, i.e. an axle that possesses circular symmetry electromagnetically. This could be either an arbitrarily shaped axle, that has similar magnetic ...
tobalt's user avatar
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Can a slanted magnetic field be created with this insulated stranded wire arrangement?

I am considering building a small-scale experimental coil gun because I have an idea of how a magnetized projectile could be rotated while it is traveling through the coil(s), similar to how a bullet ...
WaterSparkle351's user avatar
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3 answers
107 views

Inductance Computed As Length in Historical Document

In "Formulas and Tables for the Calculation of Mutual and Self-inductance.", many equations compute the inductance of an arrangement as a length. For example, Equation 95, on p. 150, states,...
Terry's user avatar
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1 answer
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EMF induction in a coil placed in a variable magnetic field

Consider a conducting coil placed in a variable magnetic field. By the laws of nature, an EMF will be induced in the coil. Between which two points is the EMF induced in the coil? If we consider it to ...
KeShAw's user avatar
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1 vote
2 answers
86 views

Turning a microwave transformer into an electromagnet

So I want to turn a microwave transformer into an electromagnet. I've already harvested the transformer, cut through the welds, and removed the coils. I want to know where to position the one coil ...
Ombrezz's user avatar
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2 votes
2 answers
177 views

Power transformer design calculations

I´m currently designing power transformers in a pretty basic way, using AWG tables for the section of the copper wire, and not knowing what are the real losses, just overdesigning. Three phase ...
samuel mattio's user avatar
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1 answer
133 views

Time average stored electric energy in a volume

I am studying the book Microwave Engineering Third Edition by David M. Pozar. At the moment I am at chapter 1.6. At the beginning of this chapter Pozar states that In the sinusoidal steady-state case,...
CircuitMan's user avatar
1 vote
1 answer
60 views

Why does inverter malfunctions when PCB is placed near metal enclosure?

I have designed a three phase inverter to drive a Synchronous motor. The motor operates fine when I place the PCB outside of the Aluminum enclosure of the motor. The voltage and frequency increases ...
Sadat Rafi's user avatar
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2 answers
79 views

Magnetically resistive material?

I'm working on an electromagnet and I'm trying to get the magnetic field further out, not necessarily stronger, just in a different place. I'm wondering if there's some sort of material that exists ...
Ombrezz's user avatar
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0 votes
1 answer
55 views

Places to harvest electromagnet coils [closed]

What are some common appliances or electronics that I can harvest a tightly wound coil and core from (like from a transformer for example)? I know about the dangers that come from messing with ...
Ombrezz's user avatar
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0 votes
2 answers
36 views

Impedance matrix of a GSG probe

I want to design a CPW that allows for high transmission. Therefore, my first guess was to find the impedance of a CPW for the even mode. I have decided to solve it from the ground up. I have used a ...
Bidon's user avatar
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0 votes
2 answers
34 views

Can the formula for magnetic field intensity be used for cores with varying cross sectional area?

Can the formula H = NI/l be used for cores with varying cross sectional areas?
Kurt Thomas's user avatar
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1 answer
39 views

Trying to understand when to use Laplace or Poisson equation

I'm trying to understand in what situations does \$\rho_v = 0\$. I know that \$\rho_v\$ is zero inside a conductor and non-zero when there is a charge distribution. The book when using has a question ...
Fernando Henrique Vaz Mello's user avatar
0 votes
1 answer
73 views

How do half-wave RF rectifiers manage efficiencies above 50%?-A theory

First off, this exact question was directly asked here EDAboard and I think it was hinted at in atleast two other posts on this exchange programmingEnthusiast, frick, by Andy AKA, who mentioned a 100% ...
Ne612we's user avatar
14 votes
1 answer
2k views

Why do these secondary transmission wires coil around the primaries?

All three primary transmission wires in the picture below have smaller wires coiled around them. These smaller wires (secondaries?) connect to a transformer and onto a nearby house. The coils follow ...
pfiers's user avatar
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2 answers
171 views

High magnetic permeability material at 100MHz

I'm doing experiments as a hobby and was trying to find a material with good (very good) magnetic permeability at least at 100 MHz (higher frequencies are even better). Ideally the material would have ...
mabeco's user avatar
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0 votes
1 answer
55 views

Add resonances to monopole antenna

How can I design a "simple" low frequency monopole antenna with multiple resonating frequencies? I elaborate... I need to design a sort of monopole antenna with multiple resonating ...
Shika93's user avatar
  • 103
-1 votes
1 answer
36 views

Electron holes and negatively charged particles [closed]

I'm studying BJTs and have a kind of legacy question. Is there any relation with electron holes and the positive charged point charges you'd see in simple Coulomb law applications?
GrillOG's user avatar
2 votes
1 answer
92 views

Magnetic Force Equation

Is there any equation where I can take a metal with a given volume/mass, with a certain amount of magnetic flux in it (in teslas) and find out how much force (in newtons) it exerts a given distance ...
Ombrezz's user avatar
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5 votes
3 answers
1k views

How can single phase induction motor's direction be reversed?

My house has a ceiling fan which has 2 wires which are connected to a capacitor, and Iam able to control the velocity and direction. After looking about these motors on the web I found out its ...
Gatonito's user avatar
0 votes
1 answer
70 views

Finding the velocity and current on a 'moving' resistor [closed]

I came across this example which to me looks kind of non-sensical. I think the Hall effect is supposed to be used to help solve this, but I struggle to use it as I think that there is some information ...
Vuko Mijušković's user avatar
0 votes
1 answer
47 views

If I have two magnets repelling each other, will they always form a peak in the middle?

If I have two identical magnets, aligned so they repel each other a distance of X apart and at a height of Z I have Hall effect sensor, the peak of the magnetic field sensed will be at the distance X/...
Ari Guðmundsson's user avatar
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0 answers
98 views

Example problem of induced emf in a coil rotating in the earth's magnetic field

I just recently learned magnetism-coil-faraday's law and I want to do some real world problem solving. Question: Let's say a copper wire coil (20 mm dimeter (r=10 mm)) of 3 turns (N=3) is on the ...
in.yssh's user avatar
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0 votes
2 answers
97 views

EMF Meter: difference between AC magnetic, AC electric, and RF Measurements

let's consider this EMF Meter. Regarding its description, I have some doubts regarding what it is physically trying to measure: Detects all three types of EMF pollution: AC magnetic, AC electric, and ...
Kinka-Byo's user avatar
  • 3,550
1 vote
0 answers
31 views

How to calculate reflection coefficient of a transmission line with discontinuity [duplicate]

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: ...
Martino Pistis's user avatar
1 vote
0 answers
32 views

How to design for an impedance matching device for non-TEM waveguides?

Let us start from the assumption that we are working with RF waveguides which do not support TEM modes. In such scenario, there is no physical (only formal) meaning to an equivalent voltage and ...
Bidon's user avatar
  • 289
0 votes
2 answers
42 views

Magnetic field generated by a current-carrying wire

When dealing with the magnetic field generated by a current-carrying wire, the formula for the magnetic flux density is B = μi/2π·d, but what if the point is located on the wire it self? In this case ...
Ahm2025's user avatar
0 votes
1 answer
47 views

Where does the electricity in electromagnets come from if permanent magnets from generators decrease their magnetic strength?

The question has been puzzling me for some time, I presume electrical power starts from generators, the heat produced by them(generators) cause their magnets to weaken and electromagnets have to be ...
kopon stanley's user avatar
1 vote
3 answers
136 views

How does all (well most of) the flux in the primary side get into the secondary side in a transformer?

I had a follow up question to this: How does a magnetic material "confine" a magnetic field? In the above question, it asks how the magnetic flux is "confined" by the core. The ...
Jonathan Lee's user avatar
2 votes
3 answers
173 views

How much more can I push current past the rating in a magnet wire?

If I have a chart like this that shows the current limit for different gauges of wound magnet wire, how much could I push the current over the limit for a short amount of time? I'm assuming these ...
Ombrezz's user avatar
  • 173
7 votes
1 answer
214 views

Equation for the force created by a solenoid

I'm trying to make an electro-magnet and I want to figure out what core and wire I need using math instead of trial-and-error. I want it to produce ~1.5 newtons of force at ~1.5 inches from the magnet....
Ombrezz's user avatar
  • 173
-1 votes
2 answers
150 views

Interpreting an EMC radiated emission test result

I am new to EMC. Our team performed an EMC radiated emission test below is the image of the test result. I am struggling to understand the result. My collegue told me that the 16 MHz clock frequency ...
Confused's user avatar
  • 2,593
3 votes
2 answers
728 views

Why does my ESP32 suffer from wifi stuttering when is next to wifi USB dongle?

I have an ESP32 connected to Wi-Fi 2.4GHz. It is positioned next to my PC's Wi-Fi USB dongle, which is connected to the same network at 5GHz. When the PC is on (the USB dongle is active), my ESP32 ...
Said Torres's user avatar
1 vote
1 answer
60 views

Wave Propagation: Attenuation Constant in a Lossless Dielectric

I am referring to M. N. O. Sadiku, Elements of Electromagnetics, 7th ed: In chapter 10, the expression for the attenuation constant α in Np/m in a lossy dielectric is derived as: $$ \alpha = \omega\...
Ryan's user avatar
  • 111
1 vote
2 answers
62 views

Core iron barely boosting field strength

I am a chemistry intern currently running a project that involves both chemistry and electromagnetism. Bottom line, I'm a little out of my depth and have much to learn, and I'm having a bit of trouble ...
LeviB's user avatar
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