Answer
To maximize the magnetic field, the wire should be short and with a large radius.
Work Step by Step
$B=\frac{\mu_0NI}{l_s}$
$I=\frac{V}{R}$ and $R=\rho \frac{l_w}{A_w}$, so $B=\frac{\mu_0NVA_w}{l_w\rho l_s}$
$V=\frac{m_{Cu}}{\rho_{Cu}}=l_wA_w$
$A_w=\frac{m_{Cu}}{\rho_{Cu}l_w}$
$N=\frac{l_w}{2\pi r_s}$
By substituting, we have:
$B=\frac{\mu_0Vl_wm_{Cu}}{\rho_{Cu}\rho_{RCu}l_w^2l_s2\pi r_s}$
Therefore, to maximize the magnetic field, the wire should be short and with a large radius.
