Introduction to
DIELECTRICITY AND CAPACITANCE
by Eric Dollard
CAPACITANCE
The phenomena of capacitance is a type of electrical energy storage in the
form of a field
in an enclosed space. This space is typically bounded by two parallel
metallic plates or
two metallic foils on an intervening insulator or dielectric. A nearly
infinite variety of
more complex structures can exhibit capacity, as long as a difference in
electric
potential exists between various areas of the structure. The oscillating
coil represents
one possibility as to a capacitor of more complex form, and will be
presented here.
CAPACITANCE INADEQUATELY EXPLAINED
The perception of capacitance as used today is wholly inadequate for the
proper
understanding of this effect. Steinmetz mentions this in his introductory
book Electric
Discharges, Waves and Impulses. To quote, "Unfortunately, to large extent
in dealing
with dielectric fields the prehistoric conception of the electrostatic
charge (electron) on
the conductor still exists, and by its use destroys the analogy between the
two
components of the electric field, the magnetic and the dielectric, and makes
the
consideration of dielectric fields unnecessarily complicated."
LINES OF FORCE AS REPRESENTATION OF DIELECTRICITY
Steinmetz continues, "There is obviously no more sense in thinking of the
capacity
current as current which charges the conductor with a quantity of
electricity, than there is
of speaking of the inductance voltage as charging the conductor with a
quantity of
magnetism. But the latter conception, together with the notion of a
quantity of
magnetism, etc., has vanished since Faraday's representation of the magnetic
field by
lines of force."
THE LAWS OF LINES OF FORCE
All the lines of magnetic force are closed upon themselves, all dielectric
lines of force
terminate on conductors, but may form closed loops in electromagnetic
radiation.
These represent the basic laws of lines of force. It can be seen from these
laws that any
line of force cannot just end in space.
FARADAY & LINES OF FORCE THEORY
Farady felt strongly that action at a distance is not possible thru empty
space, or in other
words, "matter cannot act where it is not." He considered space pervaded
with lines of
force. Almost everyone is familiar with the patterns formed by iron filings
around a
magnet. These filings act as numerous tiny compasses and orientate
themselves along
the lines of force existing around the poles of the magnet. Experiment has
indicated that
a magnetic field does possess a fibrous construct. By passing a coil of
wire thru a
strong magnetic field and listening to the coil output in headphones, the
experimenter
will notice a scraping noise. J. J. Thompson performed further experiments
involving the
ionization of gases that indicate the field is not continuous but fibrous
(electricity and
matter, 1906).
PHYSICAL CHARACTERISTICS OF LINES OF FORCE
Consider the space between poles of a magnet or capacitor as full of lines
of electric
force. See Fig.1. These lines of force act as a quantity of stretched and
mutually
repellent springs. Anyone who has pushed together the like poles of two
magnets has
felt this springy mass. Observe Fig.2. Notice the lines of force are more
dense along
AB in between poles, and that more lines on A are facing B than are
projecting outwards
to infinity. Consider the effect of the lines of force on A. These lines
are in a state of
tension and pull on A. Because more re pulling on A towards B than those
pulling on A
away from B, we have the phenomena of physical attraction. Now observe Fig.
3. Notice
now that the poles are like rather than unlike, more or all lines pull A
away from B; the
phenomena of physical repulsion.
MASS ASSOCIATED WITH LINES OF FORCE IN MOTION
The line of force can be more clearly understood by representing it as a
tube of force or a
long thin cylinder. Maxwell presented the idea the tension of a tube of
force is
representative of electric force (volts/inch), and in addition to this
tension, there is a
medium through which these tubes pass. There exists a hydrostatic pressure
against
this media or ether. The value of this pressure is one half the product of
dielectric and
magnetic density. Then there is a pressure at right angles to an electric
tube of force. If
through the growth of a field the tubes of force spread sideways or in
width, the
broadside drag through the medium represents the magnetic reaction to growth
in
intensity of an electric current. However, if a tube of force is caused to
move endwise, it
will glide through the medium with little or no drag as little surface is
offered. This
possibly explains why no magnetic field is associated with certain
experiments
performed by Tesla involving the movement of energy with no accompanying
magnetic
field.
INDUCTANCE AS AN ANALOGY TO CAPACITY
Much of the mystery surrounding the workings of capacity can be cleared by
close
examination of inductance and how it can give rise to dielectric phenomena.
Inductance
represents energy storage in space as a magnetic field. The lines of force
orientate
themselves in close loops surrounding the axis of current flow that has
given rise to
them. The large the space between this current and its images or
reflections, the more
energy that can be stored in the resulting field.
MECHANISM OF STORING ENERGY MAGNETICALLY
The process of pushing these lines or loops outward, causing them to
stretch,
represents storing energy as in rubber band. A given current strength will
hold a loop of
force at a given distance from conductor passing current hence no energy
movement. If
the flow of current increases, energy is absorbed by the field as the loops
are then
pushed outward at a corresponding velocity. Because energy is in motion an
E.M.F.
must accompany the current flow in order for it to represent power. The
magnitude of
this EMF exactly corresponds to the velocity of the field. Then if the
current ceases
changing in magnitude thereby becoming constant, no EMF accompanies it, as
no power
is being absorbed. However, if the current decreases and represents then a
negative
velocity of field as the loops contract. Because the EMF corresponds
exactly to velocity
it reverses polarity and thereby reverses power so it now moves out of the
field and into
the current. Since no power is required to maintain a field, only current,
the static or
stationary field, represents stored energy.
THE LIMITS OF ZERO AND INFINITY
Many interesting features of inductance manifest themselves in the two
limiting cases of
trapping the energy or releasing it instantly. Since the power supply
driving the current
has resistance, when it is switched off the inductance drains its energy
into this
resistance that concerts it into the form of heat. We will assume a perfect
inductor that
has no self resistance. If we remove the current supply by shorting the
terminals of the
inductor we have isolated it without interrupting any current. Since the
collapse of field
produces EMF this EMF will tend to manifest. However, a short circuit will
not allow an
EMF to develop across it as it is zero resistance by definition. No EMF can
combine
with current to form power, therefore, the energy will remain in the field.
Any attempt to
collapse forces increased currents which pushes it right back out This is
one form of
storage of energy.
INSTANT ENERGY RELEASE AS INFINITY
Very interesting (and dangerous) phenomena manifest themselves when the
current path
is interrupted, thereby causing infinite resistance to appear. In this case
resistance is
best represented by its inverse, conductance. The conductance is then zero.
Because
the current vanished instantly the field collapses at a velocity approaching
that of light.
As EMF is directly related to velocity of flux, i tends towards infinity.
Very powerful
effects are produced because the field is attempting to maintain current by
producing
whatever EMF required. If a considerable amount of energy exists, say
several kilowatt
hours* (250 KWH for lightning stroke), the ensuing discharge can produce
most profound
effects and can completely destroy inadequately protected apparatus.
* The energy utilized by an average household in the course of one day.
ANOTHER FORM OF ENERGY APPEARS
Through the rapid discharge of inductance a new force field appears that
reduces the rate
of inductive EMF formation. This field is also represented by lines of
force but these are
of a different nature than those of magnetism. These lines of force are not
a
manifestation of current flow but of an electric compression or tension.
This tension is
termed voltage or potential difference.
DIELECTRIC ENERGY STORAGE SPATIALLY DIFFERENT THAN MAGNETIC ENERGY
STORAGE
Unlike magnetism the energy is forced or compressed inwards rather than
outwards.
Dielectric lines of force push inward into internal space and along axis,
rather than
pushed outward broadside to axis as in the magnetic field. Because the
lines are
mutually repellent certain amounts of broadside or transverse motion can be
expected
but the phenomena is basically longitudinal. This gives rise to an
interesting paradox
that will be noticed with capacity. This is that the smaller the space
bounded by the
conducting structure the more energy that can be stored. This is the exact
opposite of
magnetism. With magnetism, the units volumes of energy can be though of as
working
in parallel but the unit volumes of energy in association with dielectricity
can be thought
of as working in series.
VOLTAGE IS TO DIELECTRICITY AS CURRENT IS TO MAGNETISM
With inductance the reaction to change of field is the production of
voltage. The current
is proportionate to the field strength only and not velocity of field. With
capacity the field
is produced not by current but voltage. This voltage must be accompanied by
current in
order for power to exist. The reaction of capacitance to change of applied
force is the
production of current. The current is directly proportional to the velocity
of field strength.
When voltage increases a reaction current flows into capacitance and thereby
energy
accumulates. If voltage does not change no current flows and the
capacitance stores the
energy which produced the field. If the voltage decreases then the reaction
current
reverses and energy flows out of the dielectric field.
As the voltage is withdrawn the compression within the bounded space is
relieved.
When the energy is fully dissipated the lines of force vanish.
AGAIN THE LIMITS ZERO AND INFINITY
Because the power supply which provided charging voltage has internal
conductance,
after it is switched off the current leaking through conductance drains the
dielectric
energy and converts it to heat. We will assume a perfect capacitance having
no leak
conductance. If we completely disconnect the voltage supply by open
circuiting the
terminals of the capacitor, no path for current flow exists by definition of
an open circuit.
If the field tends to expand it will tend towards the production of current.
However, an
open circuit will not allow the flow of current as it has zero conductance.
Then any
attempt towards field expansion raises the voltage which pushes the field
back inwards.
Therefore, energy will remain stored in the field. This energy can be drawn
for use at any
time. This is another form of energy storage.
INSTANT ENERGY RELEASE AS INFINITY
Phenomena of enormous magnitude manifest themselves when the criteria for
voltage or
potential difference is instantly disrupted, as with a short circuit. The
effect is analogous
with the open circuit of inductive current. Because the forcing voltage is
instantly
withdrawn the field explodes against the bounding conductors with a velocity
that may
exceed light. Because the current is directly related to the velocity of
field it jumps to
infinity in its attempt to produce finite voltage across zero resistance.
If considerable
energy had resided in the dielectric force field, again let us say several
KWH the
resulting explosion has almost inconceivable violence and can vaporize a
conductor of
substantial thickness instantly. Dielectric discharges of great speed and
energy
represent one of the most unpleasant experiences the electrical engineer
encounters in
practice.
ENERGY RETURNS TO MAGNETIC FORM
The powerful currents produced by the sudden expansion of a dielectric field
naturally
give rise to magnetic energy. The inertia of the magnetic field limits the
rise of current to
a realistic value. The capacitance dumps all its energy back into the
magnetic field and
the whole process starts over again. The inverse of the product of magnetic
storage
capacity and dielectric storage capacity represents the frequency or pitch
at which this
energy interchange occurs. This pitch may or may not contain overtones
depending on
the extent of conductors bounding the energies.
CHARACTERISTIC IMPEDANCE AS REPRESENTATION OF PULSATION OF ENERGY FIELD
The ratio of magnetic storage ability to that of the dielectric is called
the characteristic
impedance. This gives the ratio of maximum voltage to maximum current in
the
oscillatory structure. However, as the magnetic energy storage is outward
and the
dielectric storage is inward the total or double energy field pulsates in
shape or size.
The axis of this pulsation of force is the impedance of the system
displaying oscillations
and pulsation occurs at the frequency of oscillation.
ENERGY INTO MATTER
As the voltage or impedance is increased the emphasis is on the inward flux.
If the
impedance is high and rate of change is fast enough (perfect overtone
series), it would
seem possible the compression of the energy would transform it into matter
and the
reconversion of this matter into energy may or may not synchronize with the
cycle of
oscillation. This is what may be considered supercapacitance, that is,
stable long term
conversion into matter.
MISCONCEPTIONS OF PRESENT THEORY OF CAPACITANCE
The misconception that capacitance is the result of accumulating electrons
has seriously
distorted our view of dielectric phenomena. Also the theory of the velocity
of light as a
limit of energy flow, while adequate for magnetic force and material
velocity, limits our
ability to visualize or understand certain possibilities in electric
phenomena. The true
workings of free space capacitance can be best illustrated by the following
example. It
has been previously stated that dielectric lines of force must terminate on
conductors.
No line of force can end in space. If we take any conductor and remove it
to the most
remote portion of the universe, no lines of force can extend from this
electrode to other
conductors. It can have no free space capacity, regardless of the size of
the electrode,
therefore it can store no energy. This indicates that the free space
capacitance of an
object is the sum mutual capacity of it to all the conducting objects of the
universe.
FREE SPACE INDUCTANCE IS INFINITE
Steinmetz in his book on the general or unified behavior of electricity The
Theory and
Calculation of Transient Electric Phenomena and Oscillation, points out that
the
inductance of any unit length of an isolated filamentary conductor must be
infinite.
Because no image currents exist to contain the magnetic field it can grow to
infinite size.
This large quantity of energy cannot be quickly retrieved due to the finite
velocity of
propagation of the magnetic field. This gives a non reactive or energy
component to the
inductance which is called electromagnetic radiation.
WORK OF TESLA, STEINMETZ AND FARDAY
In the aforementioned books of Steinmetz he develops some rather unique
equations for
capacity. Tesla devoted an enormous portion of his efforts to dielectric
phenomena and
made numerous remarkable discoveries in this area. Much of this work is yet
to be fully
uncovered. It is my contention that the phenomena of dielectricity is wide
open for
profound discovery. It is ironic that we have abandoned the lines of force
concept
associated with a phenomena measure in the units called farads after Farady,
whose
insight into forces and fields has led to the possibility of visualization
of the electrical
phenomena.
QUESTION AS TO THE VELOCITY OF DIELECTRIC FLUX
It has been stated that all magnetic lines of force must be closed upon
themselves, and
that all dielectric lines of force must terminate upon a conducting surface.
It can be
inferred from these two basic laws that no line of force can terminate in
free space. This
created an interesting question as to the state of dielectric flux lines
before the field has
had time to propagate to the neutral conductor. During this time it would
seem that the
lines of force, not having reached the distant neutral conductor would end
in space at
their advancing wave front. It could be concluded that either the lines of
force propagate
instantly or always exists and are modified or conjugate space exists within
the same
boundaries as ordinary space. The properties of lines of force within this
conjugate
space may not obey the laws of normally conceived space.
IMPORTANT REFERENCE MATERIAL
1. Electricity and Matter, J. J. Thompson, New York, l906, Scribner's Sons,
and l904,
Yale University.
2. Elementary Lecture on Electric Discharges, Waves, and Impulses and other
Transients, C. P. Steinmetz, second edition, 1914, McGraw-Hill.
3. Theory and Calculation of Transient Electric Phenomena and Oscillations,
C. P.
Steinmetz, third edition, l920, McGraw-Hill. Section III Transients in
Space, Chapter VIII,
Velocity of Propagation of Electric Field.