At what distance from a long straight wire carrying a current of 12 A will the magnetic field be equal to $3\times {10}^{-5} \mathrm{Wb}/{\mathrm{m}}^2?$

 

Current (I) = 12 A and magnetic field (B) = 3 × ${10}^{-5} \mathrm{Wb}/{\mathrm{m}}^2$ Consider magnetic field $\overrightarrow{\mathrm{B}}$at distance r.

Magnetic field , $,B=\frac{{\mu }_{0}I}{2\pi r}$

$\Rightarrow r=\frac{{\mu }_{0}I}{2\pi B}=\frac{\left(4\pi \times {10}^{-7}\right)\times 12}{2\times \pi \left(3\times {10}^{-5}\right)}=8\times {10}^{-2} \mathrm{m}$