Made an electromagnet, curious about how this works exactly.

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Discussion Overview

The discussion revolves around the workings of an electromagnet, including the role of the iron core, the relationship between voltage and current in generating magnetic fields, and the functioning of transformers. Participants explore concepts related to electromagnetism, including magnetic flux and the behavior of magnetic fields in different contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the necessity of the iron core in an electromagnet, noting that a coil generates a magnetic field on its own.
  • Another participant explains that the introduction of a ferromagnetic core increases the magnetic flux density and relates the magnetic field intensity to the number of coil turns and current.
  • Participants discuss how the relationship between magnetic field intensity and magnetic flux density is not linear in real-world applications.
  • There is a query about whether transformers require an iron core, with a response indicating that the core enhances magnetic flux density and guides flux lines.
  • It is noted that voltage appears only when the magnetic flux density varies with time, and that applying DC current does not induce voltage in a secondary coil unless certain conditions are met.
  • Participants express curiosity about how to change voltage in a DC circuit, with suggestions including the use of voltage regulators or switching mode power supplies.
  • There is a discussion about the concept of magnetic flux, with one participant likening it to the flow of water through a filter, while another seeks clarification on how magnetism can "flow."
  • One participant introduces Maxwell's Equations to explain the relationship between electric and magnetic fields, suggesting that waves occur only when these fields vary in time.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the role of the iron core, the behavior of transformers, and the nature of magnetic flux. There is no consensus on several points, particularly regarding the implications of using AC versus DC current in transformers and the concept of magnetic flow.

Contextual Notes

Participants mention the complexity of real-world applications of electromagnetism, including non-linear relationships and the limitations of certain models. There are also unresolved questions about the nature of magnetic fields and their behavior in different scenarios.

yanom
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Hi, I'm a sophmore in high school, and I haven't taken the Physics course yet. So I'm a bit green. Anyway, I was playing around with an electromagnet I made with a nail and some 1mm wire, and I've got a few questions about the magnetism it generates:

-First, why does that iron core need to be in there? There's no current flowing through it, and from what I understand a coil already generates a magnetic field on it's own. But I can't do much with the coil itself, I've got to have that iron core.

-If I have a fixed energy supply, what makes a stronger magnetic through the coil: high voltage, low current or low voltage, high current?

-If I understand how transformers work correctly, they're simply two coils held together where one induces a current flow in another. So shouldn't a wire held up next to a powered coil show some sort of voltage? But if I do this, my multimeter can't detect any power in that second wire. So I don't understand this right. Do transformers require an iron core too?
 
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yanom said:
Hi, I'm a sophmore in high school, and I haven't taken the Physics course yet. So I'm a bit green. Anyway, I was playing around with an electromagnet I made with a nail and some 1mm wire, and I've got a few questions about the magnetism it generates:

-First, why does that iron core need to be in there? There's no current flowing through it, and from what I understand a coil already generates a magnetic field on it's own. But I can't do much with the coil itself, I've got to have that iron core.

Yes, that's true. A solenoid generates a magnetic field, but the flux intensity is greatly increased when a ferromagnetic material is introduced as the core. It happens because the magnetic field intensity is proportional to the turns of your coil and the current flowing. But, the magnetic flux density is related to the magnetic field intensity concerning the core material characteristics.

-If I have a fixed energy supply, what makes a stronger magnetic through the coil: high voltage, low current or low voltage, high current?

Maintaining the geometry and the core material, if you increase the number of turns or the current, the magnetic field intensity will increase as well. It's important to know that in real life the relation between magnetic field intensity and magnetic flux density is not linear. There are regions which can be modeled as such.

-If I understand how transformers work correctly, they're simply two coils held together where one induces a current flow in another. So shouldn't a wire held up next to a powered coil show some sort of voltage? But if I do this, my multimeter can't detect any power in that second wire. So I don't understand this right. Do transformers require an iron core too?

The ferromagnetic core has two purposes: increase the magnetic flux density magnitude and guide the flux lines within it (ideally). The voltage appears only when B (magnetic flux density) varies with time. If you are applying DC current, nothing will be noticed in the second coil, with a ferromagnetic core or not, unless you move the coil through a non uniform field, or varies the area where B is passing.

Replied inside the quote.

I'll give you some tips.
H - magnetic field intensity vector
N - turns
I - current

If you have a closed core with average length C, then you will have the following relation, excluding flux dispersion and a uniform magnetic field within the core:
|H|*C = N*I

B = u*H, considering a linear model.
u - core magnetic permeability
B - magnetic flux density vector

F = |B|*S, considering B uniform and perpendicular to the core cross section area.
F - Flux
S - core cross section area

V = d(N*F)/dt
V = voltage in a coil with N turns within a flux F.
 
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The ferromagnetic core has two purposes: increase the magnetic flux density magnitude and guide the flux lines within it (ideally). The voltage appears only when B (magnetic flux density) varies with time. If you are applying DC current, nothing will be noticed in the second coil, with a ferromagnetic core or not, unless you move the coil through a non uniform field, or varies the area where B is passing.

So transformers only work with AC current? what do you do if you have to voltage-change in a DC-only circuit?

flux
uhh... what's that? :redface:
 
yanom said:
So transformers only work with AC current? what do you do if you have to voltage-change in a DC-only circuit?

Yes, that's true. Increasing or decreasing voltage in a DC circuit is not so simple. You can use a voltage regulator which dissipates with resistors the additional voltage (very inefficient). On the other hand, if you want to increase the voltage, a more complex system such as a switching mode power supply should be used.

About flux: http://en.wikipedia.org/wiki/Flux
 
ok, thanks. So flux is flow through a surface area? Like water through a certain area filter?

Wait, how does magnetism "flow"? It isn't a type of waves/radiation, is it?:confused:
 
yanom said:
ok, thanks. So flux is flow through a surface area? Like water through a certain area filter?

Exactly.

yanom said:
Wait, how does magnetism "flow"? It isn't a type of waves/radiation, is it?:confused:

Magnetic fields and electric fields are related by the following Maxwell Equations:

55fc248faaa06562e59736f59a584870.png


b40546c7737134a147819d3cb4fdfa6f.png


E - Electric field intensity vector
H - Magnetic field intensity vector
B - Magnetic flux density vector
Jf - Free current density

Considering a linear relation between H and B in a space free of charge, you obtain the following:

5f9afae67c7f1171bf8385c21d837e81.png


That's an homogeneous wave equation. If you decompose the vector in three coordinates and solve the equations, you will obtain three wave functions.
Therefore, you will have a wave only when E or H varies in time.
 
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