1. Electric Charges and Their Properties II
Physics 2426 – Second Class
Electric Charges and Their Properties II
What is the polarization of atoms?
Figures 5
What is an induced dipole?
Conductors and Insulators
Figure P-6
Polarization of Insulators
Figure P-7 & P-9
Polarization of Conductors
Figures P-10 & P-11 (What’s Wrong)
Charging, Polarizing and Discharging

2. Perfect Conductors and Perfect Insulators
Electric charges are free to move without any restrictions to their motion.
Example - metals
Perfect Insulators
Electric charges can not move, regardless of the amount of force applied to them.
There are no static electric fields present inside perfect insulators.
Example – plastic, rubber
Reality

3. Electric Charge Distribution Handout
Do pg. 17
Charge distribution on a good conductor
Induced charge distribution on a good conductor
Transfer of charge to a good conductor
Do pg. 19 – Cylinder
Do pg. 23 – Insulator
Do pg charge distribution around corners and points
Do pg. 32 – charge questions
Assign pgs. 18, 20, 24, 27 & 34

4. Charge and Charge Density
Linear charge density – charge per unit length
Uniform charge density,
Variable charge density,
Units – C/m
Surface charge density – charge per unit area
Units – C/m2
Volume charge density – charge per unit volume
Units – C/m3

5. Charge Density Activities
Do pgs. 37 & 38
Do pg. 40
Hwk – pgs. 39, 42, & 43

6. Charge Wrap-Up Do pg. 48 Do pg. 50 Do pg. 55
Homework – pg. 49, 51 & 54

7. Fundamental “Entities”
Pages 1 & 2 in “book”
In nature there are two fundamental “entities” that we study in this course that affect their environments by their mere existence. These fundamental “entities” are
Mass
Charge
“Consequence” of these fundamental “entities” can be represented by a
Field
Force
Potential
Energy

8. Electric Fields

9. Fundamental “Entity” Mass
First, let’s look briefly at the fundamental “entity” mass
Imagine a chunk of mass in space
How do we detect its presence?

10. Electric Fields Gravitational Analogy
Gravitational Field
Consider this
business card
analogy
A more traditional
analogy is:

11. Electric Field Gravitational Analogy II
This constant “field” can be represented by
where
G is the gravitational constant, 6.67 x Nm2/kg2.
m is the source mass, the mass that creates the gravitational field
r is the distance between the source mass and the location of the business card.
is the unit vector that points from the source mass to the business card. Notice that the direction of the gravitational field, g, is opposite to this direction.
Every mass in the universe has a gravitational field described by this formula!
Every mass in the universe has the ability to “read the business cards” of every other mass!

12. Fundamental “Entity” Charge
Now, let’s look at electrical charge
Image that you have an electrical charge in space
How do you detect its presence?

13. Electric Field Pages 6 – 12 in “book”
Every object that has electric charge surrounds itself with an electric field given by the formula:
where
k is the electrostatic constant, 9.00 x 109 Nm2/C2.
q is the source charge, the electric charge that creates the electric field. Its value can be positive or negative, and is measured in coulombs (C).
r is the distance between the source charge and the point of interest.
is the unit vector that points from the source charge to the point of interest.

14. Electric Field II
Every charged object is surrounded by a field given by this relationship.
Every other charged object in the universe can “read” this field and will respond to its information by feeling an electric force.
Objects without electric charge neither create nor interact with electric fields resulting in the electric force.

15. Electric Field “Model”
Pg. 7
PhET Simulation
VPython – Lauren Watts (Sp14)

16. Electric Field “Model” II