Calculate Voltage Output Using Faraday's Law

[nebix]

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

 

[Hesch]

The relative permeability, μ_r, in air = 1.

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

PS: Could you please write the dimension in unit: [meter]?

 

[nebix]

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?

 

[Hesch]

is that where I'm getting it wrong? the permeability? it needs to be multiplied by pi?

The absolute permeability:

μ = μ_r * 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.

1910.088333 meters is the total area I calculate for my induced coil, is that what you meant?

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".

 

[nebix]

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.