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

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

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. 26 - charge distribution around corners and points Do pg. 32 – charge questions Assign pgs. 18, 20, 24, 27 & 34

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

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

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

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

Electric Fields

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?

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

Electric Field Gravitational Analogy II This constant “field” can be represented by where G is the gravitational constant, 6.67 x 10-11 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!

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?

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.

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.

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

Electric Field “Model” II