1. Warm Up 3.17.2014 3.18.2014 What is an electron?
What charge does it have?
What is a proton?
Which move easier between atoms, electrons or protons?
Note: To be graded, warm ups need to be dated. The questions should either be written into your notebook or rephrased into sentences with your answer.

2. Electric Charge
March 17 & 18, 2014

3. Electric Charge
What does it mean for an object to have an overall electric charge?
Either the object has lost or gained electrons.
If an object has gained electrons it is now negative. Why?
If an object has lost electrons it is now positive. Why?

4. The Structure of the Atom
Recall from Chemistry what happened when atoms lost or gained electrons.
An atom that loses an electron becomes a cation. It now has more PROTONs than electrons and is now POSITIVE.
An atom that gains an electron becomes an anion. It now has more ELECTRONs than protons and is now NEGATIVE.

5. Charge Interactions
We’ve all heard the phrase “opposites attract.”

6. What about alike charges?

7. Interactions with Neutral Objects
What type of interaction will a charged object have with a neutral one?
It turns out, any charged object will attract a neutral one.
Confusing huh? Let’s look at why.

8. Interactions with Neutral Objects
Neutrally Charged Balloon
Neutrally Charged Wall

9. Interactions with Neutral Objects
Negatively Charged Balloon
Neutrally Charged Wall

10. Interactions with Neutral Objects
Negatively Charged Balloon
Neutrally Charged Wall

11. Measuring Electric Charge
What units do we use to describe charge?
The Coulomb, with the unit symbol C.
1 C of charge =
6.241 x 1018 electrons

12. Coulomb’s Law
There is very clearly a force that exists between two charged objects.
How do we define it?
Recall the gravitational force between two objects.

13. Coulomb’s Law
The force that exists between two charged objects is called the electrical force. (Fe)
It has units of Newtons.
kc is known as the Coulomb’s Law constant

14. Example
A charge of -2.0 x 10-6 C and a charge of x 10-6 C are 0.50 m apart. What is the electrical force between them?

15. Fe is a vector Recall that force is expressed as a vector.
It has size AND direction.
A Fe that is negative indicates an attractive electrical force.
A Fe that is positive indicates a repulsive electrical force.

16. The Inverse Square Law
Doesn’t this pesky inverse square thing go away?
If the distance between two charges doubles, what happens to the force between them?
If the distance between two charges is cut in half, what happens to the force between them?
Force (N)
Distance (m)

17. Electrostatics Quantity Chart
Symbol in Formula
Unit
Unit Symbol
Charge q
Coulombs C
Potential Difference V
Volts
Voltage
Current I
Amperes or Amps A
Resistance R
Ohms Ω
Power P
Watts W
Electrical Force Fe
Newtons N