Magnetic Field on the Axis of a Circular Current Loop

Using Biot-Savart law, find an expression for the magnetic field at a point on the axis of a circular current-carrying loop. Hence, find the expression for the magnetic field at its centre.

The wire loop $PQRSP$ formed by joining two semi-circular wires of radii $R_1$ and $R_2$ carries a current $I$ as shown in the figure below. Find the magnitude of magnetic field at $O$.

What is the relation between current and magnetic moment of a current-carrying circular loop? Use the expression to derive the magnetic dipole moment of a revolving electron.