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

Electromagnetism issues need clearing up

  1. Nov 27, 2006 #1
    In electromagnetism, when there is an emf is induced in a secondary coil from a current flowing in a nearby primary coil (such as in a transformer), then how is the mutual inductance, number of turns of each coil, the current in the primary coil, and the emf in the secondary coil related?

    From the reading that I have been doing, I think that for a single coil:
    [tex] B = \frac{u_0NI}{2 \pi r} [/tex]
    Where the [itex]u_0[/itex] is the permeability of free space (I don't know how to get the proper symbol), [itex]N[/itex] is the number of turns, and [itex]B[/itex] is the magnetic field strength.

    From what I have gathered from the reading, is:
    [tex]E = -\frac{d \psi}{dt} = -L \frac{dI}{dt} [/tex]
    Where I have used [itex]E[/itex] for emf, and psi for the flux (I don't know how to get the convention symbol), and [itex]L[/itex] is the inductance of the secondary coil, however, I am unsure as to how the mutual inductance (M) is related to the inductance (L).

    I think the problem is that when people speak of inductance, I am unsure what they mean the inductance of.

    The reason why I am asking is that I have a question which uses this idea, but I am so close to getting it, that I would rather not post the problem in the homework section.

    Thanks in advance.
    Last edited: Nov 27, 2006
  2. jcsd
  3. Nov 27, 2006 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    L, self inductance, is the ratio of induced emf in an inductor (coil) to rate of change of current in that inductor: Emf = L dI/dt

    Mutual inductance relates to two coils in which a change of current in one coil induces an emf in the other. Emf = MdI/dt where Emf is the emf in the other coil.

  4. Nov 27, 2006 #3
    [itex]\phi [/itex]?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook