New answers tagged

3

A vertical line, with a subscript usually means "evaluate the expression before it at the value of S, where S is the subscript. However, in the absence of context, it may possibly mean something else.


0

It's possible, look for axial flux machine. But the machine has alternating poles, so the flux has a path trough metal stator and rotor, in your case you could wind all in one direction and then place a steel disk on top of that, but I have no idea why would someone use this. Another simpler way is to wrap the wire around a steel core, like solenoid coil.


2

You can wrap several bar magnets. (At least 2, but the more the better.) Pay attention to wind them equally. Align the bar magnets in parallel, so all north poles point inward. Like this Fix them in place. If you don't, they will mutually push eachother apart when you energize them. It is suggested to power them serially. That way each carries exactly the ...


0

As a Science teacher - at least until I decided to move into IT. A test tube a nail 6 inches some thickish shielded copper - seven or more loops and a basic transfer from a Science lab - In Australia we have 240 V power supply with a max 10 Amps which clearly gets transformed up in volatge down in current. A through E steps. Wrap the copper around the ...


4

In addition to the good suggestions in the other answers, the long, skinny geometry of your coil is working against you. The magnetic field is proportional to the number of turns per unit length, N/L. You've made L big, which makes the field smaller than it needs to be for fixed N and fixed current.


0

By "shunt generator" I am assuming you mean the field winding so connected directly or via a resistor onto the armature. When you start spinning the generator here is what happens. The little remaining magnetic field in the parts causes a little voltage to be produced. This little voltage makes a little field current which make it produce more ...


11

"The Cool Magnet Man" provides an excellent tutorial on the practical aspects of the design and winding of your own electromagnets here This is a summary of his procedure: Before you can start with the construction of an electromagnet, you first need to figure out the following: What will the core be made of What magnetic flux density are you ...


8

Batteries don't have much power usually. See neil's answer for how to wire them up most beneficially. If you want to obtain the highest magnetic field with smallest power from an electromagnet there are two important rules: increase the permeance of the core. This mainly equates to reduce the air gap volume . A stick core had a tremendous airgap. Better ...


26

20 AWG wire is about 33 mΩ/m, wikipedia so I'd estimate the resistance at around 3.3 Ω Into that load, your 9 V batteries are acting as current sources, not voltage sources. You will get a better match to the magnet resistance by putting them all in parallel, not series. Each battery would attempt to deliver 750 mA, which it wouldn't, but it's not as ...


1

The generated voltage is directly and linearly proportional to frequency, at least for 50 Hz vs 60 Hz. The line-to-neutral terminal voltage is the generated voltage minus the voltage drop across the armature impedance. Ignoring the resistance, the impedance at 60 Hz is 0.9 ohms. That is also proportional to frequency.


2

Interestingly, the choice of wire gauge is not so important. You can pretty much design the whole rest of the system, and then pick the wire gauge according to how you want to trade off voltage and current at any given power level (P=VI). Let's say you start with some electromagnetic system that has a coil made of AWG 21 wire... You might measure I amps at ...


5

Number of turns and current are variables that depend upon design goals. However, there is an optimization to be had in terms of geometry. A "Brooks coil" is a coil with a square cross section and an inside radius of the same dimension as a side of the square cross section. (from www.circuits.dk) The Brooks coil has the property of maximizing the ...


3

There is no ‘optimum’ but rather a compromise. A smaller cross-section wire will allow more turns but have greater resistance - this means more temperature rise. Ultimately the limiting factor is the temperature the wire insulation fails at - you want to stay away from this as far as possible. How long do you want this solenoid energized for? For short term ...


2

In equation 9.133 of Griffiths it is stated that $$\phi = \tan^{-1}\frac{\kappa}{k}$$ where (according to equation 9.125): \$\phi\$ is the phase angle between the electric and magnetic fields, \$\kappa\$ is the imaginary part of the complex wave-number \$k\$ is the real part of the complex wave-number According to Equation 9.126, one should have. $$(\frac{\...


0

I don't understand why any confusion exists. Anytime a voltage is applied across capacitor plates, an electric field will appear. Anytime a current is exists is a coil, a magnetic field will appear. Both fields contain different forms of electrical energy. In the circuit given, the capacitor will deenergize and supply the coil with a current to build its ...


1

The E Field across the capacitor plates will oscillate with the H field around the inductor wire as the right hand rule for inductor current. The E field will be present as soon as a voltage is applied or current applied to charge to a certain preset voltage, not simply after the circuit is closed. before t=0 it is a static E field condition. It will ...


0

The laws of the RLC circuits were discovered much before the electrons so just apply them and forget about atoms, electrons, attraction forces, the second law of dynamics, etc. If you really want to understand how the electrons move in a conductor you have to know quantum physics (the equation of Schrodinger). Explanations based on attraction forces, F=ma, ...


3

In addition to the other answers, I would like to add that there are two different kinds of inductance. is the usual inductance that describes the energy stored in the magnetic field. is the kinetic inductance. This happens whenever the mean free path of electrons becomes appreciable, e.g. when transversing vacuum, in superconductors or some other ...


3

Voltage and current are emergent approximations, not fundamental things. If you want to bring the velocities of electrons into consideration, then you have to understand what's going on at the quantum mechanical level. Which is hard work. Working with I and V requires ignoring the electron behaviour, just as working with pressure, which is also an emergent ...


0

For a DC electromagnet unless remanence (keeping a field after you turn it off) is a problem, you just want a high permeability so you can get a high field strength. If you check out the Wikipedia article on magnetic permeability there's a nice chart that I won't bother copying to here. From the list you can see that you obviously need Metglas because it ...


3

It depends on the conduit if it is a conductor or not. In fact the heat due to magnetic field is not from the cable but on the conduit and it is produced by the eddy currents induced by the magnetic field in the metallic conduits. That is why in case of metallic conduits cables are arranged in order to cancel the magnetic field. It is true also for three-...


0

You are right. Heat is produced by electrons flow: P(t) = R * I(t)^2 R = Rhot + Rneu Almost all the magnetic flux cancels out and all other appliances are happy.


1

Several aspects of brush design have some effect on DC motor efficiency. That would include friction, brush resistance, and contact resistance or contact voltage drop. Those items would be partly determined by brush dimensions and material. The effect would be influenced by armature voltage, current and operating speed and perhaps some other factors. For ...


2

two adjacent wires forward and return will have lower inductance as the mutual coupling reduce EMI and loop inductance somewhat But this only increases apparent power a tiny bit at 1uH/m per wire and has no effect on real power. Putting two lossy distribution lines in the same thermal resistive jacket inside a conduit ought to increase heat rise. yes a ...


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