Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Made an electromagnet, curious about how this works exactly.

  1. Mar 30, 2012 #1
    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?
     
  2. jcsd
  3. Mar 31, 2012 #2
    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.
     
    Last edited: Mar 31, 2012
  4. Mar 31, 2012 #3
    So transformers only work with AC current? what do you do if you have to voltage-change in a DC-only circuit?

    uhh... what's that? :redface:
     
  5. Mar 31, 2012 #4
    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
     
  6. Mar 31, 2012 #5
    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:
     
  7. Mar 31, 2012 #6
    Exactly.

    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.
     
    Last edited: Mar 31, 2012
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Made an electromagnet, curious about how this works exactly.
Loading...