Formula 4. Maxwell Equation of Electrostatics in Integral Form Magnetic field Electric current Vacuum permeability
$$\oint_{L} \class{violet}{\boldsymbol{B}} ~\cdot~ \text{d}\boldsymbol{l} ~=~ \mu_0 \, \class{red}{I}$$
Magnetic field
$$ \class{violet}{\boldsymbol{B}} $$ Unit $$ \mathrm{T} $$ Magnetic flux density determines the force on a moving electric charge.
Maxwell's fourth equation of electrostatics states that an electric current \(I\) causes a rotating magnetic field \(B\) and vice versa.
Closed loop
$$ L $$ Unit $$ $$ A closed loop (e.g. a circle) along which the magnetic field \(B\) is summed up by means of the line integral.
Here \( \text{d}\boldsymbol{l} \) is a small line element of the loop. The direction of \(\text{d}\boldsymbol{l}\) points tangential to the loop at each point on the loop.
Electric current
$$ I $$ Unit $$ \mathrm{A} $$ Electric current enclosed by the loop \(L\).
Vacuum permeability
$$ \mu_0 $$ Unit $$ \frac{\mathrm{Vs}}{\mathrm{Am}} = \frac{ \mathrm{kg} \, \mathrm{m} }{ \mathrm{A}^2 \, \mathrm{s}^2 } $$ The vacuum permeability is a physical constant and has the following experimentally determined value:$$ \mu_0 ~=~ 1.256 \, 637 \, 062 \, 12 ~\cdot~ 10^{-6} \, \frac{\mathrm{Vs}}{\mathrm{Am}} $$