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Homework Help: Area of a Circular Coil

  1. Jul 27, 2014 #1
    1. The problem statement, all variables and given/known data

    Please see attached image file

    I understand everything in this problem except I dont know how they got (1/4) in the area of a coil.

    Can someone explain this? I have googled it and im not getting a clear answer.

    I thought the area of a coil could be (pi(r)^2)L where l is the length. But wouldnt this be a cyclinder? How would I find it when the inner core of the cyclinder is missing?

    Thank you
     

    Attached Files:

  2. jcsd
  3. Jul 27, 2014 #2

    Orodruin

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    The coil is circular. The area of a circle is ##\pi r^2## and r is half of the diameter. The expression you gave is not an area, it has dimensions length^3.
     
  4. Jul 27, 2014 #3
    You are right. I guess I gace volume. What I really don't understand is why there is a (1/4). Could you please explain why? Thank you.
     
  5. Jul 27, 2014 #4

    Orodruin

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    r = d/2 implies r^2 = d^2/4 ...
     
  6. Jul 27, 2014 #5
    Oh ok thank you! What I did was divide the diameter in half right away. Thats why I was confused.
     
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