Magnetic Field around a dipole calculation

crystalbrite

1. The problem statement, all variables and given/known data
I've attached a page from the book Elements of Electromagnetics.

I was wondering how he gets from eq.8.20 to eq.8.21a.

What I would have done is sub in dl=a.d∅.a∅ and integrate ∅ between 0 and 2pi.

This would then give you A=[(2.μ0.I.pi.a)/(4.pi.r)].a∅

This is obviously wrong because it's not what he got. He does make an assumption that r>>a so maybe i have to do something with that.

Any help would be much appreciated

Thanks

crystalbrite

I think i forgot the attachment

Attached Thumbnails

 

crystalbrite

Its ok, i found the explanation in a book on google books. Its a bit long and tedious.

I guess no one here would be able to understand it which is why i got no reply. Oh well...