1. THURSDAY(01/22):Intro. to Ch. 18, Origins of Electricity, Charged

Objects, Electric Force, Conductors, Insulators, and Coulomb's Law.

HW: Read pages 514-18 and Solve prob. 1, 2, 3, 4, and 5 on page 543.

2. FRIDAY(01/23): Lab on Electrostatics. HW: Process all lab data and

write report, Due Tuesday.

3. MONDAY(01/26): Post-Lab Discussion. HW: Read pages 519-23 and

Solve prob. 8, 10, 14,  and 19 on pages 543-4.

4. TUESDAY(01/27): The Electric Field. HW: Read pages 523-30 and

Solve prob. 25, 29, 33,  and 37 on page 544.

5. WEDNESDAY(01/28): Review Ch.18 - Electric Forces and Fields.

HW: Complete Review Handout.

6. THURSDAY(01/29): Test on Ch.18 - Electric Forces and Fields.

HW: Go to web-site for notes on Ch.19 - Electric Potential Energy.

Very Important: If you have any questions or miss a class, see

me before school (8:00 - 8:30 AM), during Lunch, 7th hour, or

after school. Best to send an email to rpersin@fau.edu.

INTRODUCTION: In ancient Greece amber became widely valued around

1600 BC. Greeks were fascinated by it. The ancient Greek word for amber

is "elektron", meaning - originating from the Sun. The Greeks were also

the first to describe the electrostatic properties of amber. Ancient Romans

loved amber as well. From the writings of Thales of Miletus it appears that

Westerners knew as long ago as 600 BC that amber becomes charged by

rubbing. There was little real progress until the English scientist William

Gilbert in 1600 described the electrification of many substances and coined

the term electricity from the Greek word for amber. As a result, Gilbert is

called the father of modern electricity.

One of nature's most spectacular display of electricity is the lightning

observed during a thunder storm. Benjamin Franklin (1706-1790) found

that electricity originates from charges, positive or negative. We know now

that all material bodies possess electric charges. Electrons carry negative

charges while protons carry positive charges in the nucleus of an atom.

1. The electric force that stationary objects exert on each other is called the

electrostatic force. This force depends upon the distance between the two

point charges and the amount of charge on each. Experiments have

demonstrated that the greater the charge and the closer they are to each

other, the greater the force.

2. If charges have unlike signs, each charge is attracted to one other,

whereas like charges repel each other. These attractive forces and repulsive

forces act along the line between the charges, and are equal in magnitude

but opposite in direction (in accordance with Newton's 3rd law).

3. The French physicist Charles-Augustin Coulomb (1736-1806) performed

experiments with electric force between two point charges (the unit of

charge is the Coulomb, C). His work resulted in a law. Coulombs Law is

defined: The magnitude of the electrostatic force (F), exerted by one point

charge on another point charge is directly proportional to the magnitudes

of the two point charges, and inversely proportional to the square of the

distance (r) between the charges.

4. For a pair of charges q₁ and q₂, separated by a distance r, Coulomb's Law

may be stated as follows: F = k(q₁q₂/r²).

5. The constant of proportionality, k = 8.99x10⁹ Nm²/C². Such a force is

transmitted by the presence of an electric field. The electric field E due to a

point charge q is, E = F/q , or E = k(Q/r²).

6. Electric force and electric field are vectors. Hence, they have magnitudes

and directions. The electric force F and electric field E are related as follows:

F=qE, where the force is on charge q due to the presence of an electric field

at the position of q.

7. When an electric field is confined between two parallel metal plates, the

field is given by E = σ/ε_o, with σ, being the surface charge density, and ε_o

is the Permittivity of Free Space, or ε_o = 8.85x10^-12 C²/Nm².

8. The Principle of superposition also applies to the electric fields produced

by multiple charges. That is, the net electric field at a point due to several

charges is the vector sum of the electric fields due to individual charges.

9. For example, when more than two charges are present, the net force on

any one charge is equal to the vector sum of each of the forces produced by

other charges.

10. In other words, the force on charge q₁ due to the presence of charges q₂

and q₃, is the superposition of the forces exerted by q₂ and q₃. That is, the

net force F on charge q₁ is, F_net = F₁₂ + F₁₃.

where, F₁₂ is the force on q₁ due to the presence of charge q₂ and F₁₃ is the

force on q₁ due to charge q₃.

11. While solving a problem, it is useful to rewrite equation given above in

its component form as follows:

F_x = (F₁₂)_x + (F₁₃)_x

F_y = (F₁₂)_y + (F₁₃)_y

F_net = [(F_x)² + (F_y)²]^1/2

θ = tan^-1 [F_y/F_x]

12. And still, we need these steps to solve any problem in Physics:

(i) read the problem and identify the given variables

(ii) determine what you are asked to solve for

(iii) find the correct equation to use

(iv) use Algebra, Trigonometry, and/or Calculus to isolate the unknown

(v) substitute-in the given information and simplify.

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