※ 引述《ian60702 (pacific hero)》之銘言：
: A length of copper wire carries a current of i A uniformly distributed through
: its cross section,what is the energy density of the magnetic field at the
: surface of the wire?(the wire diameter is 2R)
: u(i^2)
: 答案給─────
: 8(R^2)
: 請問是不是少除了pi平方?
: 還是在下觀念有誤....煩請高手指點...感恩
B*2πR=μI
μI
B=-------
2πR
B^2 μI^2
u=------ = --------
2μ 8πR^2
好像沒錯
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