A long cylindrical wire of radius R carries a uniform current I...

Magnetic field due to long cylindrical wire of radius $R$ inside the cylinder at a distance $r < R$$\begin{aligned} & B_{\text{in }} &\left.=\frac{\mu_{0}}{2 \pi} \cdot \frac{I r}{R^{2}} \quad \text{ [where, } I=\text{ current }\right] \\ \therefore \quad & B_{\text{in }} & \propto r ...(i) \end{aligned}$$$Magnetic field outside the current carrying cylindrical wire of radius$R$at a distance$r>R$is given as$B_{\mathrm{out}}=\frac{\mu_{0} I}{2 \pi r}$i.e.$\quad B_{\text{out }} \propto \frac{1}{r}...(ii)$From Eqs. (i) and (ii), graph between$B and r$ drawn as