H Electric Forces and Electric Fields

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Electric fields have potential as a cancer treatment On Intelligence
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

The Electric Universe, by David Bodanis

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)

What is Electric Charge ?

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

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 an insulator, charge stays where it is placed

On a conductor, charge spreads out

Mechanical Universe
(click to view)

Coulomb's Law

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
Millikan's Oil Drop Experiment

How he found the charge of an electron?

  These numbers were obtained through dedicated theoretical and scientific experimentation.

You can move the individual charges!

Electrons in Orbit

The resultant force on a charge is the vector sum of all the forces acting upon it.



the pithball movie

The Electric Field

How does an electron or a proton or any other charged particle know if there is another charged particle around? Hmm. . .

A force (acceleration) that a positive test charge feels divided by its charge
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


Chapter 17 Problem #39 (wait for it to completely load---25 MB)
Click on the Picture to advance the movie forward.


for an animated gif , for static solution

Cosmic Particles light up the sky!

What causes Lightning? Wow!, II, III

It's Aliens, I just know it!

Mechanical Universe
Are the Electric Field Lines Real?

Continuous Charge Distributions


MIT CourseWare


Electric Field Lines

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!)

University of Toronto Animations
Motion of Charged Particles in a Uniform Electric Field

An Electric Field will accelerate a Charged Particle

Chapter 23 Problem 49
Quick Quiz 23