For the case of a Helmholtz coil, , and the expression for field is independent of up to its third power, and is given by,
It can be seen that the field along the axis is nearly uniform in the region between the coils.
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, and the expression for field is independent of 
up to its third power, and is given by, ![\begin{displaymath}B(z) = \frac{\mu_0 I}{a}(4/5)^{3/2}\left[1-\frac{144}{125}\frac{z^4}{a^4} \right]\end{displaymath}](../main3_clip_image066.gif)
