Questions tagged [emf]

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96 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 ...
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3answers
51 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 ...
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1answer
62 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 ...
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2answers
55 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 ...
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1answer
66 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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0answers
74 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 ...
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2answers
34 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 \...
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2answers
49 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 ...
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2answers
156 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 ...
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1answer
34 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. ...
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0answers
1k 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 ...
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1answer
115 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 ...
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3answers
496 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 ...
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0answers
23 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 ...
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2answers
42 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 ...
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1answer
26 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 ...
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1answer
229 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 ...
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2answers
100 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 ...
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1answer
87 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 ...
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1answer
44 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 ...
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1answer
43 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/...
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1answer
41 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 ...
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0answers
41 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 ...
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1answer
69 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 ...
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1answer
82 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 ...
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1answer
99 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?
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1answer
457 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. ...
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0answers
69 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 ...
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1answer
237 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 ...
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2answers
76 views

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 ...
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1answer
196 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 ...
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2answers
5k 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 ...
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1answer
46 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 ...
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2answers
110 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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3answers
3k 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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1answer
372 views

DC Shunt Motor Load Loss

I have three DC shunt wound motors in series. Each motor has a coupling to a transmission. I am trying to work out (mathematically, as opposed to intuitively), what happens if the coupling was to drop ...
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2answers
309 views

How do I connect a four way key in a potentiometer?

I asked this question in Physics stack exchange and had an answer, but I couldn't understand it well. A comment said this stack exchange was a better fit for the question. Question: How do I connect ...
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0answers
102 views

Why aren't homopolar generators more commonly used?

In particular with the advent of HVDC(high voltage direct current). Using mercury(metal), the resistive losses can be greatly reduced. There has even been some experimental research into neon plasma ...
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1answer
150 views

What happens in a generator so that we get a sinusoidal voltage as an output?

I read this online, " For a travelling magnetic field in a circle, the induced magnetic field in the armature of the generator will be sinusoidal. That's why the generated voltage is a sinusoid, ...
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1answer
242 views

Are headphones with EMF measurement of 10,000 milligauss harmful to me?

I used a EMF detector app on my phone and measured the EMF output on my wired headphones. It measured around 10,000 milligauss on one part of both ear cups. Since wearing these headphones on my head ...
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3answers
3k views

What is the SI unit of magnetic force?

As derived from F = qvB sinθ, what is the unit of magnetic force, and why? Edit: I mistakenly asked about magnetic field before. -- I'm asking the magnetic force.
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1answer
78 views

EMF from power lines [closed]

My new house flat is near an overhead power line. It's a steel structure so it's the higher energy lines. The line is about 1200 feet away at the closest point, I guess that is fairly far and you'll ...
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1answer
11k views

Calculating a voltmeter reading

I'd like to preface with saying that I'm quite new to this. Given emf E = 9 V, and that both resistances are equal, R = 1 kΩ, ...
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2answers
185 views

Strategies to reduce EMF radiation

During a long-term, almost six month long, data acquisition in a proximity of scanning electron microscope I have found a significant source of magnetic field noise, which is altering the results. I ...
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1answer
260 views

Stepper Driver signal noise problem (Ground Loop)

I have an BluePill board (Arm Cortex M3 Dev. Board). Also a a4988 stepper motor driver. BluePill is powered from usb of my PC. Stepper motor driver is powered by external power supply which is 220V -> ...
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1answer
426 views

PC monitor flickers/resets when washer motor switches on or off [closed]

My room is next to our laundry and I've recently got a new PC monitor. I've noticed each time the motor in the washing machine is switched on or off, my monitor flickers/resets. The monitor is 32" but ...
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1answer
47 views

Cancelling Ripple With A 7555

Friends, I did this once but don't remember the detail. A very sensitive circuit which switches a relatively heavy load. I used a 7555 IC to momentarily blank out any ripple or instability caused by ...
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1answer
147 views

Sparks on grounded metal bodies on lighting strikes in the nearby (two miles)

I have a strange phenomenon in our mountain cabin, on the Italian alps: lightning strike on the nearby (not so near: < 2 miles) causes audible / visible sparks on: electric / fire wood water ...
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0answers
104 views

EMF - DC Permanent Magnet Motor

I am using FEMM to design a dc permanent magnet rotor. I am trying to calculate the EMF that is induced to the rotor. Since each coil has a different position, the induced emf will be different. In ...
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3answers
652 views

Circuit approximation of Induction in guitar pickups

I was trying to learn the way basic guitar circuits work, the other day, and I stumbled upon a thing that I couldn't fully understand. According to this site, a simple guitar circuit can be made as ...