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

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

  1. Nov 8, 2015 #1
    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:

    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. jcsd
  3. Nov 13, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Nov 14, 2015 #3
    I'm having trouble following your math. Use the little ∑ button or possibly the latex markup language?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook