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Faraday's law.... need help

  1. Oct 22, 2015 #1
    so I'm trying to find the voltage output of little wireless power transfer device that I have made (I realize I could just use a Multimeter but where would be the fun in that)
    V = -N A (dB/dt)

    from what I have gathered from online research:

    N = permeability of my core which is like 1 because i'm just using air
    A = area of 1 loop in my coil which is 50.265" because my loop has a radius of 4" and 114 turns so :
    50.265 * 114 = 5730.265 area????
    B = magnetic field strength which i measured to be about 4T because my conductor has 2 turns with an air core, and 0.8amps but 600v (its a florescent light ballast), the coil is about 3/8" so about 0.375. my formula for B is = 1*2*0.8 / 0.375 = 4.2T
    dt = change in time, this was hard for me because its supposed to measure movement in seconds of the
    magnetic field / inductor but the principle of this whole project works by expanding and collapsing an
    electromagnetic field and I already don't really understand a lot of this but i really didn't get that so I
    just did some looking online and found a forum which said a magnetic field created by a 12v battery would collapsing at around 0.1 of a second so I just went with that.

    So when I finally wrote down the problem it looked like this: V = - 1 * 5730.265 (4.2/0.1)

    thanks for any help in advance, and in case its not obvious, I'm not great with math, so this is an adventure for me
  2. jcsd
  3. Oct 22, 2015 #2


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    The relative permeability, μr, in air = 1.

    So the permeabilty, μ = 1 * μ0 = 1 * 4E-7 * π

    PS: Could you please write the dimension in unit: [meter]?
  4. Oct 22, 2015 #3
    is that where I'm getting it wrong? the permeability? it needs to be multiplied by pi?

    ps: ps: 1910.088333 meters is the total area I calculate for my induced coil, is that what you meant?
  5. Oct 22, 2015 #4


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    The absolute permeability:

    μ = μr * μ0

    μ0 is the permeability in vacuum/air = 4π*10-7. So the relative permeability as for air = 1. As for iron the relative permeability is about 1000.
    So the permeability in iron is about 4π*10-4.
    Areas are measured in unit [m2], lengths are measured in unit [m].
    Both 1910m and 1910m2 is a lot as for a "little wireless power transfer device".
  6. Oct 22, 2015 #5
    Well for my purposes I am using air for my core.

    I figured that number for my area was way off but I wasn't sure because in the example I found online it said I needed to find the area of one loop in my inductor, so I figured since I have 114 loops I need to multiply the area of one loop by the number of loops I had total in the coil.
    Last edited: Oct 22, 2015
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