PX275 - B1c - cylindrical polar representation

consider a current-carrying wire, with the current, $I$ , in the $+ z$ direction
at a point, $P$ , at a distance, $ρ$ , away from the wire, the magnetic field strength is: $B = \frac{μ_{0} I}{2 π ρ}$
in cartesian system:

\vec{B} = \frac{μ_{0} I}{2 π ρ} (- \sin ϕ \hat{i} + \cos ϕ \hat{j})

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