How to make the Biot-Savart law to go around a spiral shaped coil?
The expression that I'm using is given here:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html#c4
But I want to make it such that it's calculated over a spiral, rather than a circle (as I read that what's given on the page calculates it over a circle).
Clearly I need to move into the $z$-direction, but I am unsure about how to get the $z$-coords, because the page only gives a relation between $r$, $z$ and $R$, but without $x$ and $y$.