# Formula 4. Maxwell Equation of Electrostatics in Integral Form Magnetic field    Electric current    Vacuum permeability

## Magnetic field

Unit
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

A closed loop (e.g. a circle) along which the magnetic field $$B$$ is summed up by means of the line integral.

Here $$\text{d}\boldsymbol{s}$$ is a small line element of the loop. The direction of $$\text{d}\boldsymbol{s}$$ points tangential to the loop at each point on the loop.

## Electric current

Unit
Electric current enclosed by the loop $$S$$.

## Vacuum permeability

Unit
Magnetic field constant is a physical constant and occurs whenever electromagnetic fields are involved. It has the value: $$\mu_0 = 1.256 \cdot 10^{-6} \, \frac{ \text{N} }{ \text{A}^2 }$$.