# Why is Magnetic field given as ampere per metre? What does ampere have to do here?

Isn't it just 1 coulomb of electrons passing any cross section per second? Why is it involved here in magnetism?

ToAmpere's law can be written (for static fields) $$\oint \vec{H}\cdot d\vec{l} = I_{\rm enc}\ ,$$ where $$\vec{H}$$ is the "magnetic field", which is integrated around a closed path, and $$I_{\rm enc}$$ is the current enclosed by that path.
The Biot-Savart law for a steady current gives the magnetic field as follows: $$\vec B(\vec r) = \dfrac{μ_0}{4π}\int\dfrac{(\vec I \times(\vec r - \vec r'))}{(\vec r - \vec r')^3}dl$$ Since $$\vec I$$ is in amperes, $$\vec r$$ and $$\vec r'$$ ar in meters, you get that unit for magnetic field
• Welcome! This answer (v1) assumes a system of units where $\mu_0$ is dimensionless, but in SI that constant has dimension tesla-meter/ampere. – rob Sep 12 at 15:46