Formula Magnetic Field Outside a Current-Carrying Wire Magnetic field Distance Electric current
$$\class{violet}{B(}r\class{violet}{)} ~=~ \frac{\mu_0 \, I}{2\pi} \, \frac{1}{r}$$ $$\class{violet}{B(}r\class{violet}{)} ~=~ \frac{\mu_0 \, I}{2\pi} \, \frac{1}{r}$$
Magnetic field
$$ \class{violet}{B} $$ Unit $$ \mathrm{T} = \frac{\mathrm{kg}}{\mathrm{A} \, \mathrm{s}^2} $$ Magnetic field outside a long, current-carrying wire. The magnetic field runs circularly around the wire.
Distance
$$ r $$ Unit $$ \mathrm{m} $$ Radial distance from the wire to a point outside the wire at which the magnetic field \(B(r)\) is to be calculated.
Electric current
$$ I $$ Unit $$ \mathrm{A} $$ Constant electric current flowing through the wire.