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Homework Help: Amount of energy stored in a magnetic field

  1. Apr 6, 2009 #1
    1. An air-core solenoid with 57 turns is 4.96 cm
    long and has a diameter of 1.46 cm.
    The permitivity of free space is 4×10−7 T·
    How much energy is stored in its magnetic
    field when it carries a current of 0.634 A ?
    Answer in units of μJ.
    B = mu-o (I) (N)/ L
    Induction= mu-0 (N^2/l) A
    U= (1/2) Induction (I ^2)

    3. First I calculated Induction= 4pie-7 ( 57turns ^2/ .0496m) (pi(.0146^2))= 1.3785e-5

    Then I used U = (1/2) induction (0.634 A ^2)= 2.7355μJ

    I am on the wrong path? I thought of calculating the magentic field as well
    using my first eqaution= 9.09795 e-4 T but I couldn't find the correct eqaution/ relationship to calculate the energy stored. Thanks in advance for any help!
  2. jcsd
  3. Apr 7, 2009 #2
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