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Magnetic Field of a Toroid

  1. Apr 1, 2014 #1
    1. The problem statement, all variables and given/known data
    "The toroid shown in the figure has a wire carrying a current I= 7.80 Amperes wrapped around it N= 920 times. The inner radius is R1 14.0 cm and outer radius R2 16.8cm. What is the magnitude of the magnetic field along a circle that is halfway between the inner and outer edges of the toroid?"

    2. Relevant equations
    Magnetic field of a Toroid: B=μ0NI/2πr
    B=magnetic field
    μ0=permeability constant=4πx10-7 N/A2
    N=number of times the wire is wrapped around the toroid

    3. The attempt at a solution
    Since the problem is asking for the field in the middle of the toroid, I decided to set my radius to halfway between the outside and inside:
    16.8 cm-14 cm=2.8 cm
    r=14+2.8 cm=.168 m

    When I plug in this and all the variables given to me, my answer comes up wrong. Is there a concept I'm missing? My class never covered toroids so I'm pretty much on my own for this one.

    Last edited: Apr 1, 2014
  2. jcsd
  3. Apr 3, 2014 #2
    So according to the rules I can bump the thread once after 24 hours has passed since the initial post was created? Sorry, I just really need help on this. Is it because the question is so easy to everyone else that it should be obvious what I'm doing wrong? I feel so dumb not knowing how to do this...
  4. Apr 3, 2014 #3

    rude man

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    Homework Helper
    Gold Member

    Hey man, instead of in the middle you just wound up back at the outer radius for your value of r!

    Compute r again.
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