updated: September 3, 2007
by Jeff Hawkins and Susan Blakeslee
Patterns of spatial and temporal
electrical signals are the most
fundamental currency of intelligence.
The Senses 1,2,3
The Brain 1,2,3
At a purely intellectual level the theory of electricity and magnetism, constructed by the Scottish physicist James Clerk Maxwell, is a beautiful example of mathematical clarity and predictive power. It sets the standard for how we wish to understand all the other forces of nature. Yet electricity, in the grand scheme of astonishing subjects that modern physics has thrown up, is terribly passé. On the whole, it was completely understood by the end of the 19th century.(more)
There are two kinds of charges in nature; charges of opposite sign attract one another and charges of the same repel one another.
Total charge in an isolated system is conserved.
Charge is quantized.
We really do not know why there are charges! It may have to do with some ancient cosmic broken symmetry.
The Discovery of the Electron
J.J. Thompson. . .in his own voice
Cathode Tubes
click on picture for flash
Dr. Walter Lewin, MIT
(100 megs-mp4)
Today, we know that the Electron is somewhere near the Nucleus of the Atom. Rutherford discovered the Nucleus
and Quantum Physicists gave us a more detailed and accurate picture of this world.
Mechanical Universe
The world is electrical in nature.
Nearly all atomic interactions are due to the exchange of electrons between atoms, molecules or larger structures
Your world is a dance of electrons.
Insulators and Conductors
Every material in the world can be defined in terms of how well it conducts electricity.
Certain things, such as cold glass, never conduct electricity. They're known as insulators.
Materials which do conduct electricity, like copper, are called conductors.
In the middle are materials known as semiconductors, which don't conduct as well as conductors, but can carry current.
Last, are materials called superconductors, which when brought down to very low temperatures turn into superhighways of current -- they conduct electricity without any resistance whatsoever.
(click to view)
On a conductor, charge spreads out
Mechanical
Universe
(click to view)
inverse square law
What is the physical significance of the constant known as the permittivity of free space?
"It is basically the scale factor between the unit of force and the unit of charge. There are actual electric and magnetic unit systems in which there is no such factor (since it would be 1). For most of our experiences we insist on measuring charge in coulombs and measuring forces (or electric fields) in Newtons (Newtons per coulomb). The coefficient that we need to make it come out right is related to the permittivity of free space. The words probably go back to the days when we thought there was an ether in space. You can also think about it as the way space effects the forces between two charges. In this way it becomes a property of space."
- - - Sam Bowen
You can move the individual charges!
Electrons in Orbit
the pithball movie
How does an electron or a proton or any other charged particle know if there is another charged particle around? Hmm. . .
will be defined as the Electric Field at that point. (Newtons/Coulomb)
At any point, the total electric field due to a group of source charges equals
the vector sum of the electric fields of all charges.
"Students should be led into participating in the invention of the concept and should have to articulate the purpose and the interpretation in their own words. It is through such articulation that they begin to perceive that a concept is being created for a specific purpose and cease to regard the equation above as a 'formula' received through revelation."
Arnold Arons
The Electric Universe, by David Bodanis
more
Cosmic Particles light up the sky!
Mechanical
Universe
Are the Electric Field Lines Real?
A visual representation of Electric Field
The electric field vector E is tangent to the electric field line at each point. The line has a direction, indicated by an arrowhead, that is the same as that of the electric field vector.
The number of lines per unit area through a surface perpendicular to the ilnes is proportional to the magnitude of the electric field in that region. Thus, the field lines are close together where the electric field is strong and far apart where the field is weaker.
Electric
Field Lines
The lines must begin on a positive charge and terminate on a negative
charge.
The number of lines drawn leaving
a positive charge or approaching
a negative charge is proportional
to the magnitude of the charge.
No two field lines can cross.
Electric Field lines are not real.
(Santa does not exist---though we do
seem to get presents!)
An Electric Field will accelerate a Charged Particle
Chapter 23 Problem 49
