Units Associated with Magnetic Poles
The units associated with magnetic poles and the magnetic field are a bit more obscure than
those associated with the
gravitational field.
From Coulomb's expression,
we know that force must be given in Newtons,N, where a Newton
is a kg - m / s*s.
We also know that distance has the units of meters, m.
Permeability, μ,
is defined to be a unitless constant.
The units of pole strength are defined such that if the force, F, is 1 N and the
two magnetic poles are separated by 1 m, each of the poles has a strength of 1 Amp - m (Ampere - meters).
In this case, the poles are referred to as unit poles.
The magnetic field strength, H, is defined as the force per unit pole strength exerted by a magnetic monopole, p1. H is nothing more than Coulomb's expression divided by p2. The magnetic field strength H is the magnetic analog to the gravitational acceleration, g.
Given the units associated with force, N, and magnetic monopoles, Amp - m, the units associated with magnetic field strength are Newtons per Ampere-meter, N / (Amp - m). A N / (Amp - m) is referred to as a tesla (T), named after the renowned inventor Nikola Tesla, shown at right.
When describing the magnetic field strength of the earth, it is more common to use units of nanoteslas (nT), where one nanotesla is 1 billionth of a tesla. The average strength of the Earth's magnetic field is about 50,000 nT. A nanotesla is also commonly referred to as a gamma.