Page 27 - Maxwell House

BASIC EQUATIONS OF MACROSCOPIC ELECTRODYNAMICS 7

“Whenever a prediction of the EM theory
has been subjected to experimental
verification, an agreement has been
V
obtained at any desirable level of accuracy.
Within its domain of applicability, no
observed EM phenomenon has ever been
found to contradict the classical Maxwell-
Lorentz theory of electrodynamics.” [13]
Figure 1.1.1 Voltmeter connected to the Therefore, we need to define some
battery
additional quantities, forces, and energy,
connecting the theory of electromagnetic fields with the other part of physics science (see Table
1.3).

Table 1.3
Symbol Denotation
(, ) Force raised from interaction EM fields with material objects
() Energy accumulated by electric fields (E-field)

() Energy collected by magnetic fields (H-field)

1.3 INTERNATIONAL METRIC SYSTEM OF UNITS (SI)

1.3.1 Nothing Exists Until It Is Defined and Measured in Units

To begin deriving a solution to Maxwell’s equations, it is first necessary to set a lot of quantities:
sources of electromagnetic fields, boundary, and initial conditions, basic requirements and
parameters (dimensions of all objects, their conductivity, permittivity, and permeability, etc.).
The additional critical parameters can be cost-of-production and time-of-production, the
surrounding environment influences (rain, hail, snow, wind, lightning impact, etc.). Part or all
of these quantities can come from different sciences such as physics, chemistry, etc., can be
taken from experiments, theoretical or numerical analysis. The data may often come from
different countries, where scientists may be utilizing different measurement units like meters or
inches, so it is essential first to ensure that our input value units are consistent. Mix up with
units can lead not only to an incorrect solution but to quite catastrophic consequences in real
life. In 1999, a $125 million Mars Climate Orbiter of the National Aeronautics and Space
Administration (NASA) went off its course and crashed on the Martian surface. The primary
cause was that the spacecraft engineers calculated the Orbiter’s rocket thrust in pound force ∙ s
whereas the team who built the thrusters assumed that the values were provided in Newton ∙ s.
It is not surprising that the orbiter crashed as 1 pound-force is equal to 4.54 newtons!

To avoid such kind of confusion, all used quantities must belong to the same system of units.
In electrical engineering courses, the International System of Units or SI is mandatory. SI
consists of seven base units depicted in Table 1.4. For the convenience, we also included in
Table 1.4 two dimensionless units those are not the part of base units. All other units of measure
are derived from these base units.

Table 1.4
Base Unit name Base Unit symbol Quantity name
1 Meter m Length
2 Kilogram kg Mass