The kind of magic without which all of this wouldn't be possible. This tag should be used for questions about the **physics** of the fields that charged particles create and how these fields interact. It should not be used for all questions involving electromagnetism, that would be everything on ...

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18
votes
3answers
998 views

Why isn't there a potential difference across a disconnected diode?

I know this question sounds silly, as if there was a potential difference a current would be created when the terminals are connected together and this would mean energy has come from somewhere. The ...
2
votes
1answer
48 views

Increasing the surface area of an electro magnet

I am trying to design an electro magnet with a large surface area at the end. The first design used a 1/4" rod wound with magnet wire resulting in about 10 ohms of resistance driven with 12 V. This ...
0
votes
0answers
46 views

Minimum AC voltage that causes nerve damage?

What is the minimum AC(50-60Hz) voltage that can do harm/nerve damage? I know that a few hundred volts (even 100?) has been documented to cause nerve damage that resembles a crush injury. I also know ...
0
votes
1answer
57 views

How to design a magnetic vibrator?

I plan to create a magnetic vibrator to shake a small container. What I plan is to buy Two "Magnet Wire 14 AWG Gauge Enameled Copper 1.5lb 118ft 200C Magnetic Coil Winding" a custom made container ...
0
votes
0answers
34 views

Use Earth and Ground Rods as Tip and Ring for a Modem

My co-worker and I recently tested this theory out with two Cermetek 1794A modems. Datasheet: http://www.cermetek.com/Catalog/High-Speed-Modems/DataSheet/CH1794A_607-0020.pdf Now first, we did two ...
1
vote
2answers
57 views

electromagnet question

I have an electro magnet(just nail and wire). I linked the nail/wire to 1.5 AA battery, nothing. 9V and 12V, nothing. I then linked the nail/wire to a 6V lantern battery and it pickup up the ...
0
votes
0answers
41 views

Theoretical question about electromagnetism - Uniqueness Theorem for the free space

Given the Maxwell's equations, the sources of a field and its boundary conditions, the solution found is unique, as stated by the uniqueness theorem. In the frequency domain, if the considered region ...
5
votes
4answers
332 views

Concept of 'frequency' in wire vs electromagnetic frequency in fibre optic cable

I am having trouble understanding the concept of 'frequency' of a signal in an electrical sense in a wire vs the concept of 'frequency' in the electromagnetic sense in a fibre optic cable. Are these ...
-2
votes
2answers
80 views

Is a bus bar needed?

For a short period of time, 10 kA must flow in a circuit, is a bus bar needed? I mean, since the flow of current duration is less than 0.010 seconds on a certain wire?
1
vote
1answer
36 views

EMF in an Open Circuit?

Lets assume we have a wire passing a magnetic field, it is know that EMF is induced due to the magnetic field, what if the wire is not connected to a circuit what happens? Is there ay voltage in the ...
-1
votes
2answers
71 views

If resistance is very high?

$$ V = IR $$ If there is a conductor with very low resistance, moving in a magnetic field, will it induce low EMF = IR? And a high current? Im confused at that point... Lets assume a conductor ...
1
vote
3answers
70 views

How to detect non magnetic material?

I want to design a paintball counter. I have a metallic or plastic tube through which a paint ball passes. How can I detect that the ball passed? What kind of sensors do I need? I cannot see the ...
0
votes
0answers
32 views

A conductor passing a magnetic field? [migrated]

A large thick copper wire(or bar if you like,) passes a magnetic field. What formula is best to calculate the EMF here? $$EMF = BA / Delta(t)$$ or, $$EMF = vBL$$ When the conductor passes the ...
2
votes
3answers
211 views

My DIY solenoid does not work

DESCRIPTION: Hi there, I don't know lot about electricity and I`m having problems with my first solenoid-prototype, I tried to build it watching you tube videos. I have attached the pictures of the ...
1
vote
1answer
69 views

When -EMF is induced can we keep current the same?

I'm confused at how Back EMF or (-V, -EMF) reduces current, and conserving the overall power. Let use the following simple example to help my understanding: A solenoid produces a magnetic field B, it ...
0
votes
0answers
21 views

How can simulation be fast when Electric Field is being measured with probe in CST Microwave Studio?

I am measuring the electric field in the closure box with aperture and using probe to achieve that. But I have a problem. When I use the probe for measurement, results are not accurate in transient ...
1
vote
1answer
89 views

How internal capacitor stud finders work?

I don't understand how can a non magnetic object like wood be detected using a stud finder For instance, stud finders find wood from dielectric constance, but I don't understand the princible. The ...
0
votes
1answer
33 views

Electric flux density independent of bound charge?

The electric flux density is defined as $$\mathbf{D} = \epsilon_0 \mathbf{E} + \mathbf{P}$$ where P is the polarization vector of the material. As I understand it, the net electric field includes the ...
1
vote
3answers
111 views

Why is the magnetic field perpendicular to the magnetic force?

In the case of the electric field, we define the field as the force at each point in space exerted on a unit charge. This is intuitive, as the field will give me a good idea of how a charge will move ...
2
votes
2answers
81 views

Back EMF and opposing current of a super conductor?

A 5 meter long super conductor carries 100 Amps, and it passes through a 1 Tesla magnetic field at 0.010 seconds, Is EMF = - (BL) / (t)? And since the resistance of the super conducting wire is zero, ...
3
votes
1answer
83 views

1/4 wavelength case in transmission lines

I have studied that in transmission lines, if λ is the wavelength of the signal and L is the length of the conductor, then at L=λ/4 the transmission line act as an open circuit. So if we are ...
1
vote
1answer
43 views

Lifting electromagnet & Induced EMF

An electromagnet is lifting/pulling large pieces of iron, from a distance $r$. Is there an induced EMF in the coils of the electromagnet due to the change in flux? Another configuration would be the ...
0
votes
1answer
84 views

Powerful electromagnet?

Is it possible to produce over 1000 lb of magnetic force over a distance of 4 inches(0.101 meters), using an electromagnet? How difficult would it be? Explaining the general spec's of such an ...
1
vote
2answers
102 views

Damping factor - loudspeakers and headphones

Is there any specific reason why speaker's impedance is taken into account in the damping factor formula? The Wikipedia article explains pretty well why low output impedance of an amplifier gives ...
-2
votes
2answers
76 views

How many electrons does it take to switch on a transistor [closed]

How many electrons does it take to switch on a transistor, I read somewhere that Inel had made some electrical "paths" so small that they can allow only individual electrons to flow at a time, or ...
2
votes
3answers
92 views

RSSI to distance moving average

I'm calculating distance from an RSSI, and as it seems to have quite a high variation I want to take an exponential moving average. My question is: Where in this calculation is it most applicable to ...
1
vote
0answers
88 views

Use a 2N7000 in place of 2N2222A

Here's a description of both circuits. A ring shaped magnet is mounted on a brass axle and a set of bearings. Coil A and Coil B are wound on the same core. The magnet is placed about 1/8 of an ...
0
votes
2answers
63 views

Resources for ferromagnetics

I am looking for experimental data on the experimental strength of magnetic fields inside ferromagnetic materials. Here is what I mean. If all of the magnetic moments of the molecules are aligned in ...
0
votes
4answers
107 views

How would I protect my hardware from unwanted magnetic induction?

To my understanding, magnetic induction is the process of varying magnetic fields producing a potential difference in a conductor, resulting in current. How would I protect my hardware from strong, ...
3
votes
1answer
128 views

Why do inductors release a high voltage when disconnected

I take a 12 volt battery, take a strong electromagnet, and fire it up. I then touch the two terminals that are currently connected, one terminal of the battery, and one terminal of the electromagnet. ...
1
vote
3answers
103 views

Does a battery push and pull or only push?

I've seen many analogies comparing a battery to a pump. The negative terminal pushes electrons into the wire which causes a chain reaction of the electrons in front of it moving forward, a lot like a ...
6
votes
5answers
230 views

Constant current in a circuit?

simulate this circuit – Schematic created using CircuitLab A battery pumps electrons by creating an electric field and converting electric potential energy to kinetic. Near the positive ...
3
votes
1answer
75 views

Does electricity flow in open circuits?

Say I have an open circuit with a battery. I have a wire connected to the negative terminal and a wire connected to the positive terminal. The wires aren't connected. In this scenario, would their be ...
4
votes
2answers
127 views

Why can't electrons leave the surface of a conductor?

At room temperature, no free electrons can ever leave the surface of the metal. A free electron cannot escape the coulomb (electric) attractive forces presented by the positive metal ions in the ...
0
votes
0answers
43 views

Is driving multiple electromagnets sequentially/with a duty cycle a practical thing to do?

I'm trying to play around with coils and I could use a bit of help: Does duty cycling multiple DC electromagnets save on power like it would with an LED matrix, or do their inductive properties make ...
1
vote
1answer
34 views

stepper motor losing streps at limited current

I control a stepper motor st6318 1A at 12V with a A4988 because the motor was quiet hot i limited the current to 0.76A what happen now is without any load on the motor i losing steps if i lower the ...
1
vote
2answers
101 views

Curie temperature

Does a ferrite core (or other material) have their magnetic characteristics changed when they reach curie temperature and goes below it (considering it does not suffer any mechanical damage from that) ...
0
votes
1answer
75 views

IC 555 timer to provide oscillation for high amp electromagnet

I am using a self-built electromagnet in my project that consumes 9.0 amps at supplied voltage of 12 VDC. I don't mind even if amps goes high. The power supply I am using can provide up to 30 amps. I ...
0
votes
1answer
97 views

Changing the polarity of electromagnet using H-Bridge

I have made an electromagnet using copper coil of 1.0 mm diameter, iron core of 2 cm dia & 8 cm length for my project. Supplied voltage is 12 VDC and current it consumes is 9.0 Amp. It has 1.5 Ohm ...
2
votes
1answer
92 views

AC solenoid valve with DC

I have a 24VAC/60Hz solenoid. I used 12VDC just to try, and it worked good (well needless to say it worked as expected with 24VAC/60Hz). What are the effects of a solenoid that's projected for AC ...
2
votes
1answer
95 views

Running current into a guitar pickup

When a guitar string oscillates over a magnetic-coil guitar pickup, the pickup produces an alternating current. Would it be possible to do the reverse of this, and feed an alternating current into a ...
1
vote
2answers
66 views

How can a circuit be unexpectedly affected by change in light levels?

I have (or rather, had) a completely functioning circuit the monitored input from a button to toggle an integrated LED on and off. Much to my surprise, the circuit has very suddenly become finicky ...
1
vote
2answers
207 views

How does the tester screwdriver work?

How does the tester screwdriver work? If I put the tester screwdriver inside the "hot wire" of an electrical socket, it lits up if I press my finger against the metal cap on top of the screwdriver. ...
0
votes
3answers
108 views

How do I increase the output voltage of a simple electro magnet generator

I think I know the answer to this already but I can't seem to find this on Google. The keywords are all far too ambiguous apparently. I want to create a electrical flow with a magnet passing through ...
4
votes
2answers
120 views

Electromagnetic Coil

I am trying to make an electromagnet, i would like to know what kind of core would work best, from what i have read a soft iron core would work best BUT i know some metals are known by number and i ...
3
votes
3answers
141 views

What is the physical significance of the unit ampere/meter in magnetics?

I'm having a hard time understanding what is the stuff this unit measures. I understand ampere, and I understand meter, and I understand per, but since ampere is a measure of current, I'm having ...
4
votes
2answers
127 views

What is the difference between the magnetic H field and the B field?

Wikipedia provides a mathematical explanation. Can I get the intuitive one? I'd like to, for example, understand a ferrite datasheet. These usually have graphs of H vs B, and the definition of ...
3
votes
2answers
75 views

Homebuilt magnetic tape head

I have seen a lot of projects that use a tape head, but there is very less information about how to build one yourself. Is this possible? I know that basically it is a metal core, with a coil around ...
0
votes
1answer
92 views

core and winding dimensions for an electromagnet and bifiliar winding

I am making a powerful electromagnet for repulsion for my project. I made some EMs with iron core dimensions of 1cm, 1.5cm, 2cm diameter for each 6cm and 8cm length. Different gauge enameled copper ...
0
votes
1answer
97 views

Magnetic Equivalent Circuit

Is this correct magnetic equivalent circuit for this electromagnet system ? simulate this circuit – Schematic created using CircuitLab And i am trying to solve it like this example, ...