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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
    Thanks
     
  2. jcsd
  3. Oct 22, 2015 #2

    Hesch

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    Gold Member

    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

    Hesch

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    Gold Member

    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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