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## Main Question or Discussion Point

This is part of the derivation of vector magnetic potential of a small current loop center at origin and on xy plane. The current is

[PLAIN]http://i43.tinypic.com/5f2q7d.jpg[/PLAIN]

I cannot understand why the author equate the current like this. It is constant along the loop, every other book I've seen just use I0 as constant and take it out of the integration.

Furthermore, in equation (5-5), the xyz components are represented in cylindrical co and using [itex]\phi '[/itex] to show it's the SOURCE coordinates. Then equation ( 5-6) shows the general transformation of Spherical coordinates to xyz coordinates. (5-6) does not have [itex]\phi ',\;\theta '[/itex]. But then the author combine (5-5) and (5-6) into (5-3) and the result is (5-7) that contain both [itex]\phi ',\;\theta '[/itex] together with [itex]\phi ,\;\theta [/itex]!!! This is not correct to me as this is only concerning the current along the loop, there is no involvement of any FIELD POINT in this equation. I don't even see why the author put source and field angles into the current equation.

to me

[tex] I_{(x',y',z')}=I_{(x',y')}=\hat \phi I_0= -\hat x I_x \sin\phi '+\hat y I_y\cos \phi '[/tex]

Where all angles are source angle with '. My point is there should never be any FIELD angles in the current loop equation as this is only about the current.

Please help.

[EDIT]: I read it over and over, the only way that can even make sense is if the current is observed AT the FIELD POINT. But this is very weak!!!

**stated to assumed to be constant along the loop**. Attach is the scanned copy of the page in question.[PLAIN]http://i43.tinypic.com/5f2q7d.jpg[/PLAIN]

I cannot understand why the author equate the current like this. It is constant along the loop, every other book I've seen just use I0 as constant and take it out of the integration.

Furthermore, in equation (5-5), the xyz components are represented in cylindrical co and using [itex]\phi '[/itex] to show it's the SOURCE coordinates. Then equation ( 5-6) shows the general transformation of Spherical coordinates to xyz coordinates. (5-6) does not have [itex]\phi ',\;\theta '[/itex]. But then the author combine (5-5) and (5-6) into (5-3) and the result is (5-7) that contain both [itex]\phi ',\;\theta '[/itex] together with [itex]\phi ,\;\theta [/itex]!!! This is not correct to me as this is only concerning the current along the loop, there is no involvement of any FIELD POINT in this equation. I don't even see why the author put source and field angles into the current equation.

to me

[tex] I_{(x',y',z')}=I_{(x',y')}=\hat \phi I_0= -\hat x I_x \sin\phi '+\hat y I_y\cos \phi '[/tex]

Where all angles are source angle with '. My point is there should never be any FIELD angles in the current loop equation as this is only about the current.

Please help.

[EDIT]: I read it over and over, the only way that can even make sense is if the current is observed AT the FIELD POINT. But this is very weak!!!

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