Magnetic Field Due to a Current Carrying Circular Coil

A light charged particle is revolving in a circle of radius $r$ in electrostatic attraction of a static heavy particle with opposite charge. How does the magnetic field $B$ at the centre of the circle due to the moving charge depend on $r$ ?

A circular loop of radius $r$ of conducting wire connected with a voltage source of zero internal resistance produces a magnetic field $B$ at its centre. If instead, a circular loop of radius $2r$, made of same material, having the same cross-section is connected to the same voltage source, what will be the magnetic field at its centre?