# Need help understanding the changing time portion of Faraday's law

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1. Nov 8, 2015

### jearls74

I need infomation on how to calculate the changing time part of Faradays law. The answer i keep coming up with seems very low. I learned on this forum a few years ago, and i believe i have been doing it inproperly. Here is the formula i learned:

Use
N=100
B=0.4 Tesla (static field)
A = 5 cm by 5 cm (=0.05m x 0.05m = 0.0025 m2) rotating coil
RPM = 600; rps = 10 Hz; ω = 62.8 radians per second.

So V(t) = -N·d(B·A)/dt = -N·B·dA/dt = N·B·ω·A·sin(ωt)

=(100)(0.4)(62.8)(0.0025)sin(ωt) = 6.28 sin(ωt) volts

Does this top equation produce the correct answer for induced voltage.

My parameters are as follows: - N=32
B=.5000 T
A=.00118 m2

This is how i have been calculating voltage:(1000 RPM) X (16 MAGNETS)= 16000 / 120 = 133.33Hz x (6.28) =
837.3124 w x.00118 m2 = .988028632 x .5000 T = .494014316 Volts x 32 conductors = 15.80 volts

I get a completely different number using Faradays Law equation:

( .5000 T x .00118 m2 ) = .00059 / .00119429 t = .49401736 volts x 32 conductors = 15.80 V V
d ( B X A )
-N ----------------- I got the time component
d t by dividing 1s by 837.3124 rad/s = .00119429 t

if i just use the 837.3124 radians as the time portion of the equation.

I end up with (.5000 T x .00118 m2) = .00059 / 837.3124 =7.04635450281 e-7

This last answer with the radians as the time component seems wrong.

Have i done this correct? any help is greatly appreciated.

Last edited: Nov 8, 2015
2. Nov 13, 2015