# 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.

564 questions
Filter by
Sorted by
Tagged with
21 views

### Electromagnetics - Capacitance of a two wire transmission line

This is a problem from a book. Two #16 AWG copper conductors (diameter = 1.29mm) are parallel with a separation d between their axes. Determine d such that the capacitance per unit length between ...
• 701
36 views

### Energy stored in a capacitor with dielectric

This is a problem from a book. The exact words of the problem are below: A condenser of 1 µF contains titanium oxide ($TiO_2$) as a dielecric with $ε_r$ = 100. For an applied D-C voltage of 1000 ...
• 701
1 vote
50 views

### Electrically long loop antenna with homogenous near B field inside antenna loop

I wanted to know is it possible to create a loop antenna that functions in a way like a high frequency helmholtz coil. Because a helmholtz coil is usually made with multiple turns of wire having high ...
• 31
41 views

### 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 ...
• 1,515
1 vote
62 views

### How does a Current Injection clamp work from a physics persepective?

Current injection clamps are normally described as a transformer with a single turn secondary, which is all fine and good, but the construction of a transformer is different from a current clamp. ...
• 616
28 views

### Can a photon be modeled using AC driven electron and AC driven wire loop?

Can a photon ("electromagnetic wave packet") be simulated in software as an electron bouncing up and down (for the oscillating E field) and a loop of electrons with neutralized electrostatic ...
• 103
30 views

### 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 ...
• 370
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 ...
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 ...
39 views

### TM transmission coefficent derivation

Please help, I have exams and I am not sure if my derivation for transmission coefficient for TM case is correct.
• 129
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?
86 views

### Can I use electromagnet to hold a cabinet door shut while driving (in my campervan)?

I have a bathroom/kitchen cabinet in my camper van that I keep forgetting to close correctly before driving away. Then in the first corner it'll swing open. I was wondering if I could use an electric ...
• 111
85 views

### Self Inductor - Where do I go wrong when calculating the EMF?

I have the following problem : I have a self inductor L. Its characteristics are L = 10uH and R = 12Ohm. If a current I = 200mA DC goes through L at t = 0 decreases to 1mA in 100ns, what would be the ...
218 views

### Deflection of current in a metal plate conductor

If I have a metal plate (square in shape) and an electric current moves from one side to the other. I understand that most of the current will take the path of least resistance but all paths will be ...
• 31
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 ...
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 ...
• 3,550
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 ...
19 views

### How are the currents induced by the E-field and H-field flows on a sphere? [duplicate]

Please correct me if I am wrong? We consider a sphere made of thin metal, with a radius of 1 m, at 20 km distance from an AM transmitter operating at 1 MHz. The alternating current in the transmitter ...
• 1
1 vote
105 views

### Would tempered glass be a good material to use within this simple axial flux permanent magnet motor?

I am in the design phase of building a simple axial flux permanent motor, and I am wondering if I should use a piece of tempered glass as both an insulating material and as part of the motor's frame. ...
127 views

### Re-Magnetizing A Magna-Tip Screwdriver Handle

See what I added to the bottom of this question Sorry for the high school level question. I would rather not spend my time experimenting. I have a quality gunsmith screwdriver set. The set contains ...
99 views

As a person working in a tower cab on which a ground movement radar is installed, I am curious what the typical power flux density would be inside the cab due its proximity. The frequency of the radar ...
44 views

### Magnetic Force Between 3 parallel conductors

I have a problem with 3 parallel conductors carrying currents, as shown in the picture. I need to determine the force per meter length acting on the bottom-right conductor (carrying current I2). I ...
37 views

### Phase shifting 2 waveforms to create a rotating magnetic field

I'm trying to set up a rotating magnetic field with 4 electromagnets coils (2 pairs) arranged around a fluidic cell. I have read that you need to shift the 2 waveforms out of phase by 90 degrees to ...
• 31
2k views

### Would reducing the air gap between the rotor and stator to micrometer/nanometer scale distance proportionately increase a motor's power?

I'm asking this because the smaller the distances between electromagnets, the stronger the electromagnetic field. I don't know if this would mean a proportional increase in power, be it either torque ...
• 370
275 views

### High Switching Coil Current Circuit

I've been working on building a circuit designed to handle a 40 A current with a switching time of less than 1 ms (currently using 500 us). I've attached the circuit for your review. Initially, I ...
• 23
154 views

### Measuring magnetic fields in the 1-10 Hz range

I apologize in advance but I am a chemist just venturing into the world of electrical, so you may need to explain to me like a 5 year old. I have a chemistry project that involves the use of AC ...
• 31
60 views

### 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 ...
32 views

### measuring and characterizing magnetic field of pulsed electromagnetic coil

I'm trying to measure the characteristics of a kinda-high-powered pulsed electromagnetic coil. I'm trying to characterize different coil designs, and different pulse-generators. It's operating between ...
• 11
119 views

### Why are signals reflected from an antennas dish as opposed to being absorbed?

I am trying to learn in the area of electromagnetic noise ect. I see online that a Faraday cage can work without been contected to ground (like the ones found on radio PCBs.) It sort of makes sense to ...
• 667
3k views

### Power supply makes a static/coil whine noise when the power supply is off and the PC is off

I have noticed that my power supply (PSU) makes a VERY slight coil whine/static noise while it is plugged into the power outlet, regardless of the power status of the PC and the PSU. It sounds no ...
135 views

### Reluctance concept

I would like to appeal question, where the correct answer was given as option (B) 'Cross-sectional area.' However, I believe that option (D) 'Permeance' is also inversely proportional to reluctance. ...
1 vote
164 views

### Electromagnet design and powering it up? (Fault prevention of DC supply for a small coiled Electromagnet)

I want to create an array of multiple electromagnet which I will be controlling using a microcontroller. I will have around 100 such magnets lined in a squared grid 10x10. Only three or five at a time ...
1 vote
404 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 ...
• 137
49 views

### Antennas Far field radiation pattern

I want to understand this Far field graph of an antenna generated in CST, from the picture: Is this a good radiation pattern? If yes, then how? How to explain the graph?
26 views

### ISO permitted RF emission spectrum for medical devices in hospitals

I've been searching to find the electromagnetic compatibility requirements for medical devices to be used in hospital but cannot find the correct ISO standard. The list here only lists implantable ...
• 929
89 views

### What happens when a three phase motor designed for delta connection is run star-connected? [closed]

What happens when a three phase motor designed for delta connection is run star-connected?
129 views

### Don't understand a symbol in this circuit

I'm trying to fully understand this circuit. I don't understand how the connection from the power source is going into the center of this coil. What does this represent? The circuit is for an ...
• 71
65 views

### Why is a magnetic encoder required to detect orientation of BLDC motor?

In the well known “Smart Knob” project: https://github.com/scottbez1/smartknob an magnetic encoder is used directly below the brushless gimbal motor to detect the orientation of the motor. But why is ...
• 101
1 vote
151 views

### Forms of Magnetic Noise Coupling

I was watching a video of Bob Pease discuss magnetic coupling of noise into the ground lead of an oscilloscope probe. See video at 5:40 https://www.youtube.com/watch?v=2vzvWUqUtb8 I noticed another ...
• 812
1 vote
35 views

### How to determine the length of a quarter wave transmission line which would be added to an existing circuit for impedance matching?

Are the values I have calculated accurate? With this setup, there seems to be a 90 degree phase difference across Tx2. I'm not sure if the 90 degree phase shift is supposed to across just Tx1 or ...
1 vote
108 views

### I am wondering if magnets can be safely used to connect power from one to the other? [closed]

I am thinking of trying to create a extension cord that can be taken apart or separated as needed. And rejoined at any length of cord but connected only through magnetic connections. So I'm wondering ...
• 11
39 views

### Toroidal/cylinder single turn transformer to circular waveguide coupling

The questions is mostly in the title. Is it possible to effectively couple a toroidal/cylinder shaped ferrite core with thick spread out single turn of wire to a circular waveguide? The idea is that ...
• 31
412 views

### Scattering matrix of quarter-wave transformer

I am trying to solve for the scattering parameters of a quarter wave transformer. The example that I am given is a transformer with characteristic impedance 100 Ohms, and the reference impedance (...
75 views

### Multimeter range

I've been using a small multimeter meter and the problem is that anytime I want to measure amperage that exceeds 200 mA, I have to switch the red probe the 10 A port. Unfortunately, I can't get the ...
• 339
194 views

### Visualizing current flow in transmission line

This may be a trivial question, but I am not sure how current flows in certain types of transmission lines. Consider for example a coaxial cable working in its TEM mode. The wave travels perpendicular ...
258 views

### Time-Varying Inductance in Electrical Systems

How to derive and solve equations for electrical systems when the inductance of an inductor is not constant and changes over time? I'm familiar with the standard equations like E = 1/2Li^2 or V = Ldi/...
126 views

### Design of an antenna on a PCB card emitting between 1000 and 5000 Hz

I would like to create an antena on my PCB thanks to copper track. My antenna has to be a square like a coiled coil in order to emitt a magnetic field. Is it possible to create an antenna like that ...
• 154
203 views

### How does current flow in a circuit with a capacitor, Can you please explain the concept of displacement current

When a capacitor is coupled to a DC source, current begins to flow in a circuit that charges the capacitor until the voltage between the plates reaches the voltage of the battery. How is it possible ...
• 2,593