Figure $29-72$ shows an arrangement known as a Helmholtz coil. It
consists of two circular coaxial coils,
each of 200 turns and radius
$R=25.0 \mathrm{cm},$ separated by a distance $s=R .$ The two coils carry equal currents $i=12.2 \mathrm{mA}$ in the same direction. Find the magnitude of the net magnetic field at $P,$ midway
between the coils.