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Homework Help: Magnetic field produced by a current

  1. Apr 8, 2015 #1
    1. The problem statement, all variables and given/known data
    IMG_1081.JPG this is the equation for flux density we have been given, the radius 30mm, z= goes in stages of 10mm, from zero to 50mm, then from zero to -50mm. that symbol at the begin of equation is 4 pie ! and the current is 5 amps. its is for a single-loop coil

    2. Relevant equations

    3. The attempt at a solution
    I have tried the equation and the answer is nothing like my experimental results. which is 6.2 mV, at 10mm. IMG_1082.JPG

    Attached Files:

    Last edited: Apr 8, 2015
  2. jcsd
  3. Apr 8, 2015 #2
    One of the basic formulas I've learnt is that that magnet flux density can be expressed as:
    β = μ0*I*n/2πr
    Where μ0 is the permeability vacu vacuum, n as the numbers of the turn of the coil and r is the distance to the coil :)
  4. Apr 8, 2015 #3
    thanks, but i missed something out the question, the equation is for single-loop coil
  5. Apr 8, 2015 #4
    Yep, that's the equation for singlz loops,
    Eitherway you've got 0.003 voltage difference and unfortunately these things happens due to many errors, one of them is that we're not living in the vacuum, :)
  6. Apr 8, 2015 #5


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    Hello Carl, welcome to PF :smile: !

    Please read the guidelines . You get better help if you present a clear and concise problem.
    What is this about ?
    What are the relevant equations ?

    Apparently you are measuring something in terms of mV.
    What does that have to do with the magnetic field B ?

    Also your calculations should be typed (or better: typeset). But your picture does come through clearly. Pity you don't have ##r^2## in the numerator, and it's totally unclear to me why you have ##30^2## and not ##(10^{-3})^2## in the denominator. Also, the ##10^2## should be ##(10\times 10^{-3})^2##
  7. Apr 8, 2015 #6
    thanks again, I might seem stupid, I have only done physics since Christmas , I cant see how there is only a 0.003 voltage difference ???
  8. Apr 8, 2015 #7


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    Oh, and ##\mu_0 = 4\pi \times 10^{-7}## N/A2, not just ##4\pi##.
  9. Apr 8, 2015 #8
    IMG_1084.JPG hi thanks for the advice every one, 0.01 is in the equation because the first measurement of the magnetic field was measured 10 mm away from the centre of the single loop coil, is this equation correct ?
  10. Apr 8, 2015 #9


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    I get that too. Now check that you get the right units.
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