We can see the axon as a current-carrying wire. The magnetic field produced by a current-carrying wire is given by
where
is the vacuum permeability
I is the current in the wire
r is the radial distance from the wire at which the field is calculated
The current in the axon is
,
therefore the magnetic field strength at distance
from the axon is
where
I is the current in the wire
r is the radial distance from the wire at which the field is calculated
The current in the axon is
therefore the magnetic field strength at distance
from the axon is