# Questions tagged [emf]

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### How can one calculate at surface the electric or magnetic field strength for 50Hz 240VAC wire at 1 meter depth?

How can one approximately calculate at surface the electric or magnetic field strength for 50Hz 240VAC wire buried at 1 meter soil depth for a given current? Say in sandy clay soil with no mineral ...
• 175
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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 ...
• 103
1 vote
115 views

### 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 ...
50 views

### When the electric field EMF radiation hits tin foil why does it result in a magnetic field?

I have a cheap Erickhill EMF reader that measures “electric field” and “magnetic field”. I’ve been experiencing an odd phenomena that I can’t quite explain of a electrical sound emanating from a ...
• 9
1 vote
93 views

### Back-EMF Concepts (Confusion)

I am trying to understand the current and EMF relationships in a brushless motor. Can someone tell me if this explanation is correct? Specifically, I'm interested in what is happening as the rotor ...
• 565
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### Why the LED stays on all the time in this very simple circuit?

I build the schematics from https://hackaday.com/2022/01/10/a-simple-emf-detector-and-electroscope-you-can-make-from-junk-box-parts/ but the led stays on all the time on. Why? What could be the cause ...
• 111
78 views

### Why does the emf depends on the material of the electrodes? Why is the emf independent of the distance between electrodes and amount of electrolyte?

Concise Physics mentions that: The emf (electromotive force)of a cell depends on 1) the material of the electrodes and 2)the electrolytes used in the cell.However it is independent of the a)the shape ...
133 views

### Constant Voltage Applied to Inductor

I'm seeking clarity on understanding what happens when a constant voltage is applied to an inductor. I gave this explanation in another thread and it was regarded as wholly misguided in the following ...
121 views

### Inductor Back EMF Direction Relative to Changing Current

I have spent a lot of time thinking about Faraday's law and common explanation as given on wikipedia does not sit well with me. I may be confused. My concern is entirely with the wording of this ...
1 vote
164 views

### Microcontroller 24V digital output

For a microcontroller generating a 20mA industrial digital output. What kind of setup is best? I'm considering: Microcontroller pin driving a low current N-FET to pull a 24V signal to ground. But ...
• 25
69 views

### Wireless charging shielding requirements

I have a project where I want to throw a charging coil into the wonderful mix of tiny parts but the problem is, I also need an accelerometer/magnetometer roughly right beside said coil. I believe I ...
1k views

### How should I understand back-EMF in an inductor?

I have a circuit made of a MOSFET that pulls the lower side of an inductor to ground while the other side is connected to a DC voltage source as follows: Then it is very simple to describe what's ...
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772 views

### Why does analysis indicate that ground lifts do not fix ground loops?

Note: "Ground loop" in this question refers to a ground loop caused by linked magnetic fields. (Sometimes ground loop refers to slightly different scenarios.) Recently I've been looking into ...
71 views

### Identifying strange readings from Arduino EMF detector

Intro and knowledge self assessment Full disclosure, I'm an amateur, and my knowledge of electronics is cursory, and I'm more into computer science. But I bought an knock off arduino kit, and decide ...
1 vote
126 views

### Motor Noise Reduction + PWM

I'm trying to suppress EMF coming from a brushed DC motor that I am running. I've tried using 0.1uF capacitors across the motor leads as discussed here: https://www.pololu.com/docs/0J15/9. It works ...
• 11
100 views

### Is it normal to have around 40 V in your body, when touching your plugged, ungrounded laptop?

I have had bilateral shoulder pain and then both arms and hands pain for around 7 mounts, which got much worse when I started working from home, with my laptop. The ultrasound of shoulder muscles ...
66 views

### Do switches induce voltage spikes in the AC power grid?

I know that DC inductive loads create back EMF when turned off and that's why we use a freewheeling diode. Does this also true for AC inductive loads and AC loads in general? I know we can't use a ...
1 vote
63 views

### Isn't the voltage reading in this image wrong?

The conductor is moved from top to bottom through the B-field. Shouldn't the reading be negative on the volt-meter? Right-hand-rule gives that the positive charges experience a force towards us. Then ...
• 217
151 views

### How is it that the induced EMF in an alternator is in quadrature with the main flux?

Looking at the simplified diagram of an alternator, the flux "linked" with the conductor is maximum at 90, 270 degrees, is also when induced EMF is maximum. So isn't the main flux in phase ...
• 801
168 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 ...
91 views

### Where are the sensors of the EMF/RF meter on the circuit board?

In the attached photo you can see the PCB of a simple EMF/RF meter. This meter shows, at the same time, the values of the electric field, magnetic field, and power density (see small illustration on ...
• 13
52 views

### EMF and voltage on inductor

What is difference between EMF given as $\epsilon=-L\frac{dI}{dt}$ and voltage on inductor $V=L\frac{dI}{dt}$? In circuit analysis is $V$ used as the voltage on inductor, and why is it equal to \...
60 views

### Permanent magnets inside electric motor create stress

I am trying to do a simple project, a brushed DC motor, in my free time to check what I learn in lessons in real life and I've encountered something I didn't think of before while studying the EMF ...
• 87
240 views

### How exactly does a basic EMF sensor work?

Halloween is coming up, and inspired by the simplicity of this project, I'm asking for a more technical explanation (and / or resources to do that) - this seems to be either missing or too obvious to ...
• 287
1 vote
39 views

### What will be the graph of flux of coil 2?

In the following picture current is flowing through coil 1. Let's assume that current is increasing linearly in coil 1. Then emf induced in 2nd coil be will constant and having some negative value. ...
• 25
2k views

### Elaborated difference between static and dynamic EMF

I have seen two sources have contradicting takes on static and dynamic induced EMFS. One source says that Static EMFs are produced by the circuit and magnetic field both being stationary. Dynamic EMFs ...
• 429
167 views

### Mesh to block or reduce wireless cell signals

I want to block or reduce the amount of wireless cell signals coming into my house through my window(s) by using some type of mesh (screen). I could use a sheet of metal but then I wouldn't be able ...
• 37
830 views

### Measuring back EMF induced current with multimeter

I have built a solenoid with copper. It is 19 cm long, it has 64 turns and the radius is 1.5 cm. To trigger back EMF, I use a permanent magnet that has the same surface as the cross sectional area of ...
1 vote
26 views

### EMF radiation from an open AC circuit

When I pass my EMF radiation meter near an electricity cable (a cable that is connected to the home mains), it shows me that there is a radiation. But if there is an extension cable for example, and ...
1 vote
46 views

### Motional Emf confusion

I know that in motional emf V=Blv where B,l,and v are perpendicular to each other. When one of them isn't, then there would be no emf. What formula supports this?(mathematical evidence) Can anyone ...
38 views

### How will equivalent EMF and resistance of cells be calculated

In the image, three cells are arranged in a circuit. But the cell in the centre is installed such that the positive terminal is connected to the positive terminal of one cell and the negative terminal ...
• 267
405 views

### Harrington rod from spinal fusion might be acting like a human EMF antenna [closed]

In 1994, I had a spinal fusion surgery to correct Scoliosis which was a result of my medical condition, Spinal Muscular Atrophy Type II. I've used a wheelchair my entire life. Because my upper body ...
• 309
428 views

### Should I be worried about a surge protector near my pillow

I have just realized how close my surge protector appears to be to my pillow. It is about 20-30cm away. Should I be worried about any EMF/radiation/something else? The surge protector itself is new ...
• 109
91 views

### Which EMF frequncies provide power to field powered implants? [closed]

What EMF frequencies provide power to field powered implants? There are in ear phones and some implants which obtain power through EMF fields. They produce sound in the ear and some other implants are ...
54 views

### How do I calculate the regulation of the generator in a Ward-Leonard system?

I have a DC motor with independent excitation, power by a ward-leonard system. The nominal voltage applied to the motor is 250 V. I have to calculate what regulation(%) to apply to the generator so ...
• 187
1 vote
45 views

### Question: AC Voltage and Current variables

So I know how alternating current is produced, but I'm curious to what determines the voltage and amount of current moving within the wire. Does the frequency of the alternations give more voltage/...
46 views

### Grabbing EMF meter magnifies signal 10fold

I have a Tenmars tm‑195. Holding it in my hand arm's length, still, I read $2 \mu W / cm^2$. In exactly the same spot, without me holding it, I read 10 times lower, $0.2 \mu W / cm^2$. I can ...
• 113
47 views

### Shield EMF from power cable with aluminium foil

There is a big electric cable behind a wall. On the other side, I read around $2 \mu W / cm^2$ of EMF at distance about 3 feet from wall. Is there any way to shield this using aluminium foil? I ...
• 113
1 vote
74 views

### Is it normal for 24" LED monitor to emit 1000 odd mV/m?

I have a 24" LED monitor, we have a cell phone tower on a building next to ours, so we bought an EMF meter to see if there was any high radiation from it. Throughout the house, the radiation was above ...
169 views

### How to calculate the emf with flux density given instead of flux

So I have the following question What is the emf in a coil of 2000 turns and c-s area 10cm2 when a flux density of 0.4T density in it is reversed, i.e. in a time of 20ms. Also what would be the the ...
1 vote
124 views

### Is there a way to measure or predict how much a 10.5 microns Aluminum foil attenuates EMF radiation? [closed]

Is there a way to measure or predict how much a 10.5 microns Aluminum foil attenuates EMF radiation? And at what frequencies? Is it enough to use as Faraday shield?
1k views

### Back EMF of an H Bridge

I am building a H bridge to control a motor in the middle. As an example, when power is fully removed (24V... 80V in the picture below), there is some back EMF that will drive the 24V input rail. ...
117 views

### Hall effect current sensor and proximity to EMI

I am preparing to layout a PCB. I have an ACS723, that I want to use to sense the current going through a relay. In addition to the relay I have a Meanwell IRM-12-20 to supply ac to dc voltage to the ...
• 264
1 vote
325 views

### Pancake Coil Magnetic Field Strength

I am trying to measure the magnetic field strength of a pancake (flat) coil. I know the turns, inner radius, current, and frequency from an AC input and am trying to measure the magnetic flux so I can ...
• 133
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### Charging a capacitor with a ferromagnetic generator

I am doing my internship and the company is making a ferromagnetic generator which indeed uses magnetic transition to create a flux and finally EMF. I am assigned to design a circuit which takes the ...
279 views

### How does DC braking stop an AC motor without considering current direction?

When a motor is coasting to standstill, if I apply a DC voltage across the windings I will brake that motor... We'll at least that's what I've read. Now here's the thing. With reverse current ...
• 317
8k views

### Why is the air gap between the stator and rotor on a motor kept as small as it is?

Between the stator windings and rotor is a small air gap. What would happen if this gap were larger than it is? Surely the magnetic field set up by energizing the stator windings would still cut the ...
• 317
51 views

### How Does Resistance Affect EMF Measurements?

I have very little electrical engineering knowledge, but am working on a simple Arduino project that detects electromagnetic fields. The original project specifies that three 1M resistors should be ...
113 views

### Does 20 Millegausse near outlet with nothing plugged in suggest faulty wiring?

Meterk EMF meter showing 20+ millegausse near two outlets only. Both outlets have nothing plugged in. Possible live and neutral wires faulty?
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5k views

### EMF - Dangerous uT levels? [closed]

Live in 7 floor apartment building directly above electrical room for entire building and old elevator. Noticed static electricity or excessive charge and have been investigating. Measured EMF ...
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