# Questions tagged [emf]

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### Are multiple EMF sources considered series-opposing in a parallel circuit? [closed]

In the parallel circuit attached, is it correct to call the loop A-B-I-J series-opposing? Or is B-I just another leg of a parallel circuit? Asked another way, does an opposing EMF source such as BAT1 ...
1 vote
128 views

### What are sources of extra low frequency magnetic field in a car with IC engine? [closed]

ELF analyser (16 Hz - 2 kHz) shows a magnetic field around 300- 2000 nT (at some position exceeding that) in car when petrol or diesel engine work. When RPM increase from idle to 2500 RPM, magnetic ...
148 views

### Example problem of induced emf in a 100 turn coil by a 100 turn coil which has 90kHz sin wave input voltage

Main Question: Let's say there are two coils each 100 turn and diameter 30 mm, And the second coil is perpendicular to the first coil's magnetic field (placed both coils next to each other; we can see ...
• 45
98 views

### Example problem of induced emf in a coil rotating in the earth's magnetic field

I just recently learned magnetism-coil-faraday's law and I want to do some real world problem solving. Question: Let's say a copper wire coil (20 mm dimeter (r=10 mm)) of 3 turns (N=3) is on the ...
• 45
64 views

### Example problem of induced emf in a coil travelling with some velocity and perpendicular to the earth's magnetic field

I have a example problem which I created myself just out of curiosity, Question: Let's say a copper wire coil(20mm dimeter(r=10mm)) of 3 turns(N=3) is moving along the surface(Note-coil is not ...
• 45
92 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 ...
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1k views

### How do transformers work?

I am a recent EE graduate and never really understood how transformers work. I am having trouble understanding how voltage is increased at the expense of current in a step up transformer. I understand ...
99 views

### Offshore windfarm and real life effects on ocean fish [closed]

An offshore windfarm is being proposed which will consist of 170 wind turbines that will produce 1100MW of power. The offshore substations will utilize 15 miles of export cable. Part of their ...
46 views

### Increasing power of a standalone circuit board

I am a rookie at potentially upgrading some electronics and wanted to see if I could get a little direction on a potential first project. I purchased a small frequency generator and would like to ...
46 views

### Why +ve charge(conventional current) flows out of the -ve terminal of a battery?

Please consider question 45 part c. In this question if I consider that the capacitor after being fully charged at 24V is now connected to a 12V battery, and since some heat will be lost as charge ...
1 vote
101 views

### Does AWG affect ethernet cable picking up EMF from electrical lines?

Currently, I have a client running an inappropriate cat 5E cable through a buried conduit, underground from their house to their pool control unit. This conduit also facilitates two lines of 120 V. ...
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56 views

### Magnetic Field Produced By Electromagnet Perpendicular Winding

If I wound wire like a cylinder (blue) and then continued in a perpendicular direction like a toroid (yellow), what would the magnetic field look like?
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1 vote
211 views

### Shunt's thermal EMF (Seebeck effect) vs Kelvin connection?

While reading this Vishay document about shunts, I saw that temperature mismatch between the shunt's terminals can introduce a "parasitic" voltage drop which will in turn affects the current ...
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949 views

### When is a zero-crossing SSR recommended for switching power to heating elements?

I am going to be switching power to three 2.7kW heating elements (240VAC, ~11.1A each) using a microcontroller. I'm trying to decide between mechanical relays and SSRs. The mechanical relays are much ...
1k views

### How can I clamp the voltage precisely from the back EMF of a brushed DC motor?

I am using DRV8412DDWR in a medical product, where we are driving two DC motors (graphite brushed) bidirectional using PWM. In our application, we have to suddenly stop the motor. When we do that, we ...
• 41
208 views

### How to find the terminal voltage of a series generator given output power and EMF?

A 12 kW, 120 V DC series generator has a series field resistance of 0.05 Ω. The generated EMF is 135 V when the generator delivers the rated load at its rated terminal voltage. The armature resistance ...
115 views

### How do we calculate the cross section area and EMF in a solenoid?

Case 1: Consider an air core solenoid $S_0$ with inner diameter $(d_{in0})$ = 10 cm and the cross section area of the wire = 0.1 cm, outer dia $(d_{out0})$ = 10.1 cm. The number of turns in the ...
121 views

### Coil for biggest EMF

I have a short (<1 s) pulse output that will be around 20 kV. Frequency is around 100-200 kHz. How would I make a coil that induces the biggest electromagnetic force (to radiate and mess with the ...
• 77
83 views

### Why do I have to connect ground to earth for my board to work?

I built a 3d printer myself, Im using an off the shelf controller board with a 24v 400w led power supply that I found for cheap on AliExpress. The quality of the power supply is far from perfect,It ...
211 views

### Understanding back EMF current in DC

I am trying to make a kicker solenoid. My circuit is: 12 V battery connected to DC step-up booster 300 V diode A10A. The diode is rated for 10 A and 1000 V. thyristor BTW69-1200 with external ...
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150 views

### Induced EMF polarity of inductor from bar magnet

I can't understand the polarity of an induced emf of an inductor from a bar magnet. I understand inductor voltage polarities in normal closed circuits in that an inductor produces a voltage drop when ...
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1 vote
85 views

### Induced EMF in wireless LED

I have already asked this question here but this may be a better place. I have built the following circuit to power a wireless LED but my calculations and measurements do not give the same values. I ...
• 113
104 views

### Inconsistent readings of magnetic fields between two electric vehicles

I measured the strength of magnetic field in two electric vehicles from different automakers. Both measurements were done while the vehicle was driving at non-trivial speed. Vehicle 1 showed under 0....
104 views

### Fixing traverse on Guldmann GH2 (old title: Measuring EMF and terminal voltage with multiple batteries)

Suppose we have two 12V batteries as our source voltage. How can the EMF and terminal voltage be measured when using one 12V battery versus both batteries? Since terminal voltage deals with a closed ...
1 vote
1k views

### Are those electric fields dangerous?

Is 8.6 amperes per meter, 70 microtesla, 0.70 gauss, 695 milligauss, safe on long time exposure? I am just worried.
1 vote
205 views

### Is an analog radio tuner more robust in a nuclear blast than a digital tuner?

Some radio receivers seem to have analog tuners (i.e. you turn a knob and it's completely mechanical), whereas others are more digital i.e. they can search for stations, save them as "presets&...
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1 vote
198 views

### Will primary flux & secondary flux (back MMF) in a transformer attract or repel each other?

I couldn't find it on google or may be I am not using the right keywords, if my terminologies are not sounding accurate, please bear with me, I am beginner in electrical engineering. When the primary ...
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188 views

### How can I find the damaged phase in an RC drone's brushless DC ESC?

I have a damaged RC drone/quad. It has an all in one FC/ESC. The "all in one" is brand new. One of its motors is twitchy/does not spin. That motor is tested to be good. I tested it by ...
1 vote
69 views

### Thermoelectric EMF problem for low voltage measurement load cell

The resolution of a load cell is highly dependent on its capacity. That's because the higher the resolution and the higher the capacity, the smaller the voltage change. For example, many companies ...
205 views

### How does a CAT 4 radio detector work in passive mode?

According to https://www.radiodetection.com/sites/default/files/Theory-Buried-pipe-manual-V10.pdf in passive mode a CAT 4 radio detector 'looks' for harmonics produced on the 50/60Hz mains buried ...
108 views

### 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 ...
1 vote
118 views

### 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 ...
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1 vote
841 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 ...
• 147
187 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 ...
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1 vote
379 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 ...
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220 views

### 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 ...
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586 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 ...
851 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 ...
799 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
1k 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 ...
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### 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 ...
2k 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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1k 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 ...
158 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
1k 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 ...
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114 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 ...
168 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
66 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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