What is the magnetic field strength at the centre of a single circular loop of radius R carrying current I?

1. At the centre of a circular loop the field is B = mu0 I / (2 R), with R the loop radius. 2. This is similar in form to the straight-wire result but without the factor pi. 3. It is valid only at the centre of the loop, not at other points. 4. With N loops instead of one, the field becomes N times as large. 5. Multiplying by R rather than dividing would make a bigger loop give a bigger central field, which is backwards. _Source: OpenStax College Physics (CC BY 4.0), Ch 22 "Magnetism", section 22.9 Magnetic Fields Produced by Currents: Ampere's Law_