Magnetic Field around a dipole calculation

[crystalbrite]

Homework Statement

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

 

[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...