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The current density inside a long, solid, cylindrical wire of radius $a=3\mathrm{.}6mm$ is in the direction of the central axis and its magnitude varies linearly with radial distance $r$ from the axis according to $J=J_0\frac{r}{a},$ where $J_0=340\frac{A}{m^2}.$ Find the magnitude of the magnetic field at a distance $($a$)r=0,($b$)r=2\mathrm{.}1mm$ and $($c$)r=3\mathrm{.}6mm$ from the center.

$($a$)$ Number

Units

$($b$)$ Number $$ Units

$($c$)$ Number $$ Units