1. Electrostatics
From our previous discussions in class you do remember the four fundamental interactions in the universe,
Can you name them?

3. Four Kinds of Forces Strong Nuclear Force: Weak Force:
A strong force that holds the particles of the nucleus of an atom together. Short range attractive force that is much larger in magnitude to the gravitational or the electromagnetic forces.
Weak Force:
Force involved in transmutation of particles within the nucleus. Only observed/viewed in radioactive decay. Stronger only than the gravitational force.

4. Four Kinds of Forces Gravitational Force: Electromagnetic Force:
Attractive force that exists between all objects. The gravitational force between the Earth and the moon keeps the moon in orbit. It may be the most evident but it is the weakest of all the forces.
Electromagnetic Force:
Charged particles at rest or in motion exert electric forces on each other. They give materials their strength, their ability to bend, squeeze, stretch or shatter. When charged particles are in motion they produce magnetic forces on each other. Electric and magnetic forces are both considered to be aspects of this single force.

5. Electromagnetic Force
We are going to study electromagnetic force and its effects and importance on our world for the next couple of months
To start we look at electric charges at rest called……….

6. Study of properties and results of electric charges at rest
Electrostatics
Study of properties and results of electric charges at rest
Atom is Neutrally Charged – Positive charge on the nucleus is exactly balanced by the negative charge of electrons
Atom

7. An Electron can be removed from an atom to create a positive ion
Electrons
Freed electron can be:
Unattached and Free – Creating a negative charged particle
Attached to an atom – Creating a negative Ion

8. Electric Forces There are two kinds of electric charges:
Positive – protons – p+
Negative – electrons – e-
Charges exert a force on other charges over a distance.
Like charges repel.
Unlike charges attract.
Electroscope = Instrument to determine charge.

9. Materials can be of three kinds:
Insulators – Materials that inhibit the flow of free charged particles
Examples: wood, air & rubber
Conductors – Materials that allow the flow of free charged particles
Examples: metal & water
Semiconductors – Intermediate class, conduction between an insulator and conductor

10. Charging by Conduction
Charging of Objects
An object can be charged either through conduction or induction
Charging by Conduction - - - - - - +
Charging a neutral body by touching it with a charged body - +

11. Charging of Objects Induction
An object can be charged either through conduction or induction -
Induction - - -
Charging a neutral object by bring a charged body close to but not touching the object. + + - +

12. Charging of Objects Charging by Induction
An object can be charged either through conduction or induction - - - - - + + +
Charging by Induction - - + + +

13. Charging of Objects Charging by Induction
An object can be charged either through conduction or induction - - - - - + +
Charging by Induction + + - -

14. Charles Coulomb
Charles Coulomb ( ) was a French physicist and military engineer. Because of his expertise with simple machines, he was able to build an apparatus to measure the electrical force between two charged objects. He derived a law, Coulomb’s Law, which gives the relationship between charges, their separation and the electrical force of attraction or repulsion.

15. Coulombs Law
Coulombs Law states that the size of the electric force between two charged particles depends on the size of the charges and the distance between them.
q is a unit of charge measured in coulombs “C”
r is the distance between the charged objects
K is a constant = 9.0 x 109 Nm2/C2

16. Coulombs Law e- = -1.60 x 10-19 C p+ = +1.60 x 10-19 C
The charge on one electron or one proton is called an elementary charge
e- = x C
p+ = x C
One coulomb of charge has
6.25 x 1018 electrons or protons
One lightning bolt may have 10 C of charge

17. Millikan Oil Drop Experiment
Robert Millikan
American physicist who determined the charge on an electron using charged oil drop experiments in 1909.

18. Millikan Oil Drop Experiment
What Millikan did was to put a charge on a tiny drop of oil, and measure how strong an applied electric field had to be in order to stop the oil drop from falling. Since he was able to work out the mass of the oil drop, and he could calculate the force of gravity on one drop, he could then determine the electric charge that the drop must have. By varying the charge on different drops, he noticed that the charge was always a multiple of
-1.6 x C, the charge on a single electron. This meant that it was electrons carrying this unit charge.

19. The Millikan oil-drop experiment was far superior to previous determinations of the charge of an electron. Where other workers had attempted to measure the quantity by observing the effect of an electric field on a cloud of water droplets, Millikan used single drops, first of water and then, when he found these evaporating, of oil. The experiment had broader significance than a simple refinement of a number. Millikan emphasized that the very nature of his data refuted conclusively the minority of scientists who still held that electrons (and perhaps atoms too) were not necessarily fundamental, discrete particles. And he provided a value for the electronic charge which, when inserted in Niels Bohr's theoretical formula for the hydrogen spectrum, accurately gave the Rydberg constant—the first and most convincing proof of Bohr's quantum theory of the atom.