There is a spiral which has \(r_i=3\,\text{cm\), \(r_{ext}=6\,\text{cm}\), \(I=20\,\text{mA}\) and \(N=200\), where \(r_i\) : internal radius \(r_{ext}\) : external radius \(N\) : number of turns \(I\) : current. Find the magnetic moment of the spiral.}