First things first…• Charge is represented by the unit ‘Coulomb’• What is charge?• What is a Coulomb?

Quick Question• There are two flavors of electric charge: + and –, brainstorm the

reason for giving each charge this particular name.

What particles are typically associated with these charges?

Bell WorkGiven the information we know about static electricity so far:

-How might we utilize static electricity to our benefit?

Interesting Findings:https://www.youtube.com/watch?v=PQJud3Eh0tk

What is STATIC ELECTRICITY?Definition: An imbalance of electric charges within or on the

surface of a material.

Materials that Can Cause Static Electricity

Insulators vs. Conductors

Polarization

How can objects become charged?

Friction• Electron affinity• Triboelectric series

Conduction

Induction

Bell Work: Connection to the past

• When two charges (positive & positive, negative & negative, or positive & negative), are placed closely to one another, what do they start to do?• Discuss with your neighbor what this mean the charges are exerting?

Hint: Think of this question in terms of Newton’s 2nd law……

Have homework on charging on desk to be collected.

Charles Coulomb

Coulomb’s Law

Q. What does each of these variables mean: Fe , k, q, and r?Q. What are the units on these variables?Q. Dig deeper into k, which is explained through the constant ϵo ,

what is this?

𝐹 𝑒=𝑘𝑞1𝑞2𝑟 2

Definition: the measure of the resistance that is encountered when forming an electric field in a medium…

(in this case a vacuum, expressed through the ‘o’).

So, what really is a ‘field force’?

ϵoThe Permittivity of Free Space

Coulomb’s Law

𝐹 𝑒=𝑘𝑞1𝑞2𝑟 2

Newton’s Law of Gravitation

𝐹 𝑔=𝐺𝑚1𝑚2

𝑟 2

These are two VERY similar equations. Break each equation down, and think of how each variable is related to the

others.Q. Use these two equations to solve for the magnitude of force exerted by

both the Electric & Gravitational forces of a proton and an electron…

Now, some problems…• Two charges feel an attractive force of 36 N, what will they feel if…

A. The distance between them is tripled?

B. The distance is doubled and one of the charges is tripled?

C. Both charges are tripled and the distance is tripled?

?Hmmmm…..• Based on your calculations, why would it seem that Gravity is the

ruling force in our galaxy, despite being significantly weaker than the electrical force?

Talk to your partners, and come up with strong, logical reasoning.

Video Time• https://www.youtube.com/watch?v=2HhaQtvICe8

Robert A. Millikan

Bell Work• Identify 2 ways to calculate the gravitational force.• Identify 1 way to calculate the electric force.• Define ‘equilibrium’?• With a partner, discuss the meaning of ‘static equilibrium’.

Using what you now know about the relationship of Newton’s Law of Gravitation and Coulomb’s Law, create an

equation/relationship, that represents the system in static equilibrium, to determine how much charge a plate must have to levitate a .01 kg balloon with 4 µC of charge at a height of 5

cm?

1. Create an equation/relationship.Note: There is more than one way to calculate Fg

2. Plug in the numbers to solve.

Static Equilibrium

Soooooo…How do we know what the charge is on a single electron?

Brainstorm how you might do this?

Because of Millikan’s Experiment…• Calculating the number of electrons/protons that make up some charge is

possible!

So, how many electrons make up a -1 C charge?

By the way, I highly suggestkeeping a running record of common

constants we use, like charge and mass of particles.