[領域]                             (題目相關領域)
電磁學
[來源]                             (課本習題、考古題、參考書...)
Griffiths  Problem 6.12(b)
[題目]
An infinitely long cylinder, of radius R carries a"frozen-in" magnetization

parallel to the axis  M=ks(方向為延著+z軸)

where k is a constant and s is the distance from the axis;there is no free

current anywhere.

Find the magnetic field inside and outside the cylinder by two different

methods:

(a)As in Sect. 6.2, locate all the bound currents, and calculate the

field they produce.

(b)Use Amperes law to find H, and then get B from H=B/u0 - M


[瓶頸]                             (寫寫自己的想法，方便大家為你解答)

(a)沒什麼太大的問題  但是在寫(b)的時候不知道H的方向要如何判斷

看了詳解 他只寫因為對稱性所以H為+z方向....然後就寫下安培定律了

可是我還是搞不懂+z方向是怎麼看出來的

不知道有沒有可以對於(b)來個詳細一點的解答呢?  感謝

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