Question

What will be the magnetic field at a distance r when an electric current flows through these things ?

Answer 1

When current flows through a wire, magnetic field is produced around it, quantitatively expressed by Ampere's law.

Magnetic field around straight wire is $\frac{{\mu }_{0}I}{2\pi r}$

Magnetic field in a current carrying loop is $\frac{{\mu }_{0}I}{2r}$

Magnetic field in several turns of wire is ${\mu }_0\frac{N}{l}I$