Question:

A circular coil of closely wound N turns and radius r carries a current I. Write the expression for the following: (i) the magnetic field at its centre (ii) the magnetic moment of this coil

(i) : Magnetic field at the center B = μ₀IN/2r
(ii) : Area of the coil A = πr²
∴Magnetic moment of the coil μ = INA = πr²IN