# Formula Current-Carrying Wire (Inside) Electric current    Radius    Distance

## Magnetic field

Unit
Magnetic field inside the wire increases linearly with the distance to the center of the wire. The B field runs in cylindrical coordinates in the $$\varphi$$ direction.

## Electric current

Unit
Current in the long straight wire.

Distance from the center of the wire to a location $$r$$ inside the wire where the magnetic field is to be calculated. Here the formula is valid only for inside the wire: $$r ~\le~ R$$.
Vacuum permeability is a physical constant with the value: $$\mu_0 = 4\pi \cdot 10^{-7} \, \frac{ \text{N} }{ \text{A}^2 }$$.