B is the magnetic field, in teslas, at any point on the axis of
the solenoid. The direction of the field is parallel to the solenoid axis.
μ_{o} is the permeability constant (1.26x106 H/m)
i is the current in the wire, in amperes.
N is the total number of turns of wire in the solenoid.
l is the length of the solenoid, in meters.
r is the radius of the solenoid, in meters.
x_{1} and x_{2} are the distances, on axis,
from the ends of the solenoid to the magnetic field measurement point,
in meters.
