Questions tagged [emf]
The emf tag has no usage guidance.
91
questions
1
vote
1answer
33 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. ...
0
votes
0answers
24 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 ...
0
votes
1answer
111 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 ...
6
votes
3answers
332 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
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 ...
1
vote
2answers
40 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 ...
0
votes
1answer
25 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 ...
-2
votes
1answer
150 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 ...
0
votes
2answers
56 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 ...
-2
votes
1answer
85 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 ...
0
votes
1answer
40 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 ...
1
vote
1answer
41 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/...
0
votes
1answer
40 views
Grabbing EMF meter magnifies signal 10fold
I have a Tenmars tmā195. 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 ...
0
votes
0answers
37 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 ...
1
vote
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 ...
0
votes
1answer
51 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
1answer
92 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?
0
votes
1answer
200 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.
...
0
votes
0answers
52 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 ...
1
vote
1answer
174 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 ...
3
votes
2answers
70 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 ...
0
votes
1answer
155 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 ...
2
votes
2answers
3k 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 ...
-1
votes
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 ...
0
votes
2answers
108 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?
-1
votes
3answers
2k 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 ...
1
vote
1answer
313 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 ...
0
votes
2answers
207 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 ...
0
votes
0answers
84 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 ...
0
votes
1answer
102 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, ...
-4
votes
1answer
212 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 ...
-1
votes
3answers
2k views
What is the SI unit of magnetic force?
As derived from F = qvB sinĪø, what is the unit of magnetic force, and why?
Edit: I mistakenly asked about magnetic field before. -- I'm asking the magnetic force.
0
votes
1answer
70 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 ...
1
vote
1answer
6k 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 kĪ©, ...
0
votes
2answers
145 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 ...
-1
votes
1answer
213 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 -> ...
0
votes
1answer
316 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 ...
0
votes
1answer
46 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 ...
6
votes
1answer
135 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 ...
0
votes
0answers
89 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 ...
2
votes
3answers
504 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 ...
0
votes
1answer
39 views
What is the canonical form based on sinus of the autoinduced EMF in a coil
I am stuck with this exercise as I can't really find the expressions I need in order to solve this. Please help me & guide me theoretically, so I can finish this.
Deduce the canonical form based ...
0
votes
1answer
56 views
Using 2 Tank Circuits to Determine the Position/Direction of a Wire
I am building a robot that uses 2 LC tank circuits with some gain and analog filtering to determine the position of a "Track Wire" that has an AC current of a specific frequency traveling vertically. ...
1
vote
2answers
897 views
Zener diode for solenoid
I am new in electronics and this is old subject but still. I started new Arduino project where I control 4 solenoid valves independently via Arduino 4 chanel 5 V Relay module. From the beginning I put ...
0
votes
1answer
165 views
A simple motor using Copper coil
This is a simple motor made with a magnet, a battery and a copper coil.
I am curious to know how can it be explained using physics.
I know that the copper is diamagnetic but not enough that it can ...
2
votes
1answer
193 views
Is there an actual need for the concepts “emf” and “back emf”?
Given a two-terminal element where you can only measure the voltage across terminals \$v(t)\$ [\$v_{ab}(t)\$] and the current \$i(t)\$ defined as entering the positive [a] terminal, there doesn't seem ...
9
votes
2answers
1k views
Thermal EMF (seebeck effect) on PCBs
Can poor PCB fabrication process / assembly, and the type of solder used cause thermal EMF (seebeck on PCB) problem? Is it affected by the type of the material used? For example, quality of plating, ...
2
votes
2answers
90 views
Using an analog temperature sensor near 3-phase 150V , 40A Motor Controller?
I'm looking for suggestions on what type of temperature sensor to use. I need to have it attached to the heat sync of a 150V, 40A 3-phase motor controller. The motor controller is in a enclosed space ...
0
votes
3answers
100 views
Question about coil emf
Hi I am a Korean student studying physics. Recently I was solving a physics problem about coil emf and I have a question.
As you see in this circuit and the graph, when you close the switch the emf ...
0
votes
1answer
155 views
Question about Stepper Motors
I have a need to sometimes manually turn the lead screw on a stepper motor controlled CNC system (which I have not purchased yet). So IF I put a switch in the wires of the stepper motor and open the ...
