1. Electrostatics: Electricity at Rest
Chapter 16
Electrostatics:
Electricity at Rest

2. Facts About the Atom Protons Neutrons Electrons
positive charge, don’t move
Neutrons
no charge, don’t move
Electrons
negative charge, move

3. Facts About the Atom
Atoms normally have equal p+ and e- and are therefore neutral
To have a charge they must gain or lose the electrons

4. Electrical Charges
Fundamental Rule:
Like charges repel
Opposite Charges Attract

5. Conservation of Charge
Total amt. of charge remains the same but may be rearranged.
Ex: a rubber rod is rubbed with fur, electrons are transferred from the fur to the rod
Ex: a plastic rod is rubbed with silk, electrons are transferred from the rod to the silk

6. Conductors vs. Insulators
Conductor – electrons can move easily
Metals
electron sea
Insulator - Tightly bound electrons
Rubber
Glass

7. Creating charge by Induction
Bring charged item near neutral conductor and it will polarize its charge

8. Forces Newton’s Law of Universal Gravitation F = G m1m2 d2 Attractive
Depends on mass
G = small magnitude = weak force

9. Forces Coulomb’s Law F = k q1q2 d2 Attractive or Repulsive
Depends on Charge
k = large magnitude = strong force

10. Coulomb’s Law F = k q1q2 d2 k = 9.0 x 109 N•m2/C2
Unit of Charge - Coulomb (C)

11. Coulomb’s Law
Sirap rubs two latex balloons against her hair, causing the Balloons to become charged negatively with 2.0 x 10-6 C. She holds them a distance of 0.70 m apart. What is the electric force between the two balloons?

12. Coulomb’s Law
When sugar is poured from the box into the sugar bowl, the rubbing of sugar grains create a static electric charge. If two sugar grains each acquire a charge of 3.0 x C at a separation of m, with what force will they repel?

13. Coulomb’s Law
Two balloons acquire a charge of 2.0 x 10-7 C each. How large is the electric force between them when they are separated by a distance of 0.50 m?

14. Coulomb’s Law
A raindrop acquires a negative charge of 3.0 x C as it falls. What is the force of attraction when the raindrop is 6.0 cm from the end of a car antenna that holds a charge of 2.0 x 10-6 C?

15. Coulomb’s Law
In a grain elevator, pieces of grain become electrically charged while falling through the elevator. If one piece of grain is charged with 5.0 x C while another holds a charge 2.0 x C. What is the force between them if they are separated by m?

16. Lightning!! Clouds build up static electricity
Ground is inductively charged
Discharge!!!
Lightning rods – slowly drain charge
Use Ellen’s Video – start at 7 minutes to discuss how clouds get charged
2 reasons for lightning rods