# 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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### Transient analysis of inductor circuit and back EMF

In a lecture exercise from a circuit course, I encountered the following circuit with only an inductor and a voltage source. The $v$ vs $t$ and $i$ vs $t$ graph is as follows: -The KVL ...
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### How does an inductor store energy?

I know that the capacitors store energy by accumulating charges at their plates, similarly people say that an inductor stores energy in its magnetic field. I cannot understand this statement. I can't ...
4k views

### 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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### Magnetron Working Principle

I was reading this simple description of magnetron working principle. Can you explain me why when electrons go near the cavities, they start to resonate at microwave frequency? I do not see the link ...
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### Not able to levitate magnet for magnetic levitation project

I am following a hackster project on magnetic levitation here - https://www.hackster.io/jsirgado/magnet-levitation-with-arduino-eeeee4 However, I have followed everything but still, it's not working. ...
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### Are there types of standard coaxial cable with a propagation velocity of 0.9c? What would be the application?

Reading this answer I was surprised to hear that there are "excellent" kinds of coaxial cable with a propagation speed of 0.9c; 90% the speed of light. The bargain basement number is about 2/3c, and ...
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### Electromagnetic shielding and EMP

I've asked several related questions, but I'm afraid that some of the answers that I received, while great answers, might be skewed because of incorrect assumptions or unclarity in my questions. The ...
• 321
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### How can a DC spark create EM waves?

I have a question please about sparks used in the early history of radio. I have read the similar questions but I still need your help please. I have learned from sources such as https://neurophysics....
1k views

### 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 ...
8k views

### Difference between a magnetic field sensor and a hall effect sensor

I can't understand the difference between a magnetic field sensor and a hall effect sensor, to me are both the same. I have a voltage detector pen that I can use when I troubleshoot my house I ...
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### Propagation 'speed' of EM waves in air versus through conductive material

This paper I was reading said: "At a high level, the propagation speed of EM waves through conductive materials is SLOWER than their speed in air". Don't conductive materials intrinsically have less ...
600 views

### What's the circuit diagram symbol for a variable reluctance sensor transducer?

I know I've seen the symbol before, it's something like a circle with an open triangle facing in the direction of current flow with a line through the middle. I'm specifically thinking of the ...
261 views

### Why does a loop antenna not measure the differential magnetic field?

I am making the assumption that a loop antenna is essentially an inductive loop and behaves as such, please let me know if this is incorrect. Knowing that the voltage (emf) across an inductor is ...
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723 views

### Meaning of reflection coefficient in English

So I know a reflection coefficient of 0.5 angle 30 at the load (k=0m) means "At this point, 50% of the incident wave is reflected and has a 30 degree phase shift." But what does it mean in ...
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### Is the resistance in a DC Motor constant if the voltage is?

Is resistance in a DC motor constant if both the load and voltage are constant as well?
1 vote
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### Homemade Electromagnet from Microwave oven transformer

I want to make an electromagnet in order to perform this trick I have taken the following parts from a microwave oven, and following some instructions i have made the following electromagnet: I have ...
1 vote
297 views

### Voltage on a Transmission Line with Ideal Conductors

Let's consider a transmission line with Perfect Electric Conductors. We know that if an external AC source is applied, we get a voltage waveform between the conductors which is function of the ...
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1 vote
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### How to increase an electromagnet's magnetic field size?

I made this electromagnet out of a microwave oven transformer by taking out the secondary coil. It very strong but it can only attract the metals if I bring it really close. How do increase the ...
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1 vote
1k views

### How to make the electromagnet of a magnetic-levitator?

I saw pictures of magnetic-levitators on the internet. That's amusing. I wanted to make one of those. So I started searching in Google. And I found out that these devices have a big electromagnet ...
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1 vote
234 views

### Designing AC kick solenoid lock

I am making a kick solenoid lock with AC. I designed the circuit to run on 220 V, 50 Hz (household plug.) The inductor (coil) is air core 500 turns, 150 meter (500 ft) in length with inductive ...
1 vote
456 views

### Is ferrite core inductance similar to iron?

My 0.5" (1/2 inch) iron core inductor did not have a high inductance due to (I assume) eddy currents. Theory seems to suggest that ferrite cores are the ticket to increase inductance. I ordered ...
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1 vote
971 views

### How is the current induced in this circuit?

Rectangle FBCE is the conducting wire. The circle is where magnetic field exists.The perimeter of the circle is NOT a conducting wire. R1,R2,...are different resistances. If the magnetic field(B) is ...
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1 vote
307 views

### Slow solution of LTSPICE electric-magnetic model for transformers

I am trying to model a transformer using coupled electrical and magnetic circuits. SPICE has many advantages in assembling these circuits. I was able to model properly for an transformer with no load, ...
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1 vote
881 views

### Detecting a low pulse from an electromagnet induction

I am designing something similar to a coil gun. So what I have is a magnet passing through/adjacent to a coil. Due to the electromagnetic induction, I do get a pulse(triangular) across the coil. ...
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1 vote
239 views

### Is .95J worth of work within 1 second Equivalent to .95W of Power?

This is a question that has two parts to it divided up into two sections. It is similar to the "Is Work done to Transfer Energy?" question but has been refined to include the conversion from Joules of ...
1 vote
151 views

### Is Work done to Transfer Energy?

The example below is for a perfect lossless circuit with no resistance for the sake of illustration only. In reality this does not exist, but again the purpose is for simplicity. If there is 1 Joule ...
1 vote
290 views

### Contradicting ideas about differential signal route, confining fields vs Increasing impedance

By initial sense I think we must: keep pair intra-distance as close as possible for field cancellation. Fill surround of pair with GND plane and have via near to it to confine the fields, prevent ...
1 vote
105 views

### What are the mechanism and effects of non-linearity in an attenuating barrier in the presence of a high-strength EM field?

It's my understanding that in electromagnetics, if an attenuating device is functioning linearly, it means that 1) input and output signal strengths are proportional; and 2) input f = output f. How ...
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### Strength of a pulsed electromagnetic field

Forgive me if my question sounds a bit naive: I have built a coil (no solid core) out of an insulated copper wire, and I calculated that it has 8 ohms of resistance. I tried it and it gave me the ...
197 views

### 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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### Accurately detecting distance from current carrying wire

I am trying to find a way to accurately detect the distance from a stretched wire for alignment purposes (within 10um). I am not concerned with the absolute value of the distance, rather the ...
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### Find the current flowing in the load of a transmission line?

My Try: $Z_{in}=Z_0*\frac{Z_L+jZ_0tan\beta l}{Z_0+jZ_L tan\beta l}$ Now $\beta l=\frac{2\pi\times37.5\times10^6\times10}{3\times10^8}=\frac{5\pi}{2}$ so its becomes $Z_{in}=\frac{Z_0^2}{Z_L}$ \...
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### What is the consideration when installing or replacing the shaft of an induction motor?

Here are two picture of my washing machine's motor. I am not sure whether you still have such that machine in your country. It is a top loading washing machine's washing motor (a another smaller one ...
6k views

### generator coils: max power given wire gauge

I've been messing around with some neodymium magnets and magnet wire to make a generator. I've rotated my rotor as fast as I could and noted the no-load voltage. I wondered if (at this current speed) ...
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### How to insert background EM noise into pathloss equation?

I am trying to understand how to add the background noise into the equation. I am trying to work out the pathloss of a radio signal over a certain distance. We have the Friis Formula for that for ...
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### How do I correctly calculate the resistance (induced emf?) of a generated current against the flux? [closed]

I have all the basic physics working for every major section of the entire generator as correctly as I think I can (barring actual code implementation improvements) but just couldn't get the feedback ...
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### Simple wireless power transfer circuit question

source: https://circuitdigest.com/electronic-circuits/simple-wireless-power-transmission-circuit-diagram Above circuit is the very simple wireless power transfer circuit, but I could not find any ...
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### What can I use to increase efficiency of inductive wireless energy transfer instead of factory manufactured ferrite plates?

The Context I am a hobbyist with no education in electrical engineering. I am working on a DIY project trying to make water resistant rechargeable bicycle lights. I am doing this as a hobby for fun ...
3k views

### Phase of Scattering Parameters

I do not understand the meaning of the phase of scattering parameters. Let's consider for instance a two port network, and let's focus on S21. I know that its absolute value represents a ratio ...
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### Can a "static" magnetic field carry Information? [closed]

Information is electronically represented as some energy that is changing, therefore we measure an on state (1) and an off state (0), to create a (0,1) binary representation of the information. Now a ...
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### Magnetic Field vs E-M Field

I have got some questions on this topic based on the best answers I get to these: -1- If magnetic fields arise due to electric currents in conductors, we say they are not E-M waves in nature; it is ...
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### Voltage drop through a resistor compared to a Zener diode

A variant of this question has been asked a few times, but not received a response. Usually, we get an analogy with water pressure, or gravity, or a version of Ohm's law; not the actual cause-effect ...