OpenStax University Physics/E&M/Sources of Magnetic Fields

For quiz at QB/d_cp2.12
Free space permeability $$\mu_0=4\pi\times 10^{-7}$$ T·m/A Force between parallel wires $$ \tfrac F\ell=\tfrac{\mu_0I_1I_2}{2\pi r}$$ Biot–Savart law $$ \vec B=\tfrac{\mu_0}{4\pi}\int\limits_{wire}\frac{Id\vec\ell\times\hat r}{r^2} $$ Ampère's Law:$$\oint\vec B\cdot d\vec\ell=4\pi\mu_0I_{enc} $$ Magnetic field inside solenoid with paramagnetic material =$$B=\mu nI$$ where $$\mu=(1+\chi)\mu_0$$= permeability