1. Electrostatic Charge Transfer

2. How do objects get charged? • Electrons can move • Conductors • electrons are “free” and can move throughout the material • in good conductors, can move from atom to atom, and object to object • Insulators • do not allow free movement of electrons throughout the material, or from the object to other things • Charges within objects are separated • Neutral atoms/objects • equal protons and electrons • Charged atoms/objects • more or less electrons than protons (depending on charge)

3. Law of Conservation of Electric Charge net charges must equal zero

4. Within and object: • If part of an object becomes charged, the other part of an object must become equally and oppositely charged. • Example: water molecules Negative Pole Positive Pole Net overall charge: 0

5. Between 2 Objects: • If an object becomes charged from interacting with another, the other object must become equally, but oppositely, charged

6. 4 Ways to Charge Objects #1: Polarization • Surface charge (object remains neutral, overall) • Charges within object shift • in response to being near a charged object • Only while near the charged object.

7. Lightning

8. Lightning • Friction causes build-up of electrostatic charges in clouds • Bottom of cloud is usually negative • Negative buildup repels electrons in the ground, so surface becomes positive. • With enough buildup • Electrons are attracted to the earthand come down in a “streamer” of negative charges. • Positively charged air particles near the surface of the earth are repelled by the ground and form a “streamer” upwards. • When the streamers connect, a conductive path for an electron surge is formed – lightning occurs! • Air particles are so excited they emit light • Air is heated so intensely in creates sound waves (thunder)

10. Polarization Demo • Watch the demo and answer the questions on your worksheet.

11. Experiment #1 Charging by polarization. • Rub the round end of the balloon with the fur for a few seconds. • Hold the balloon against the wall and release it. • Observe what happens.

12. 4 Ways to Charge Objects #2: Friction • Electrons transfer between objects by rubbing 2 neutral objects together (objects must have different affinities for electrons)

13. Charging by Friction

14. Experiment #2 Charging by friction. • Rub one of the balloons on your hair for a few seconds. • Immediately hold it close to the other balloon. • Observe what happens.

15. 4 Ways to Charge Objects • #3: Conduction: • - Requires one charged object, & one neutral object. pith ball simulation

16. Step 1: Objects brought together to touch • Step 2: electrons transferred from charged to neutral (but polarized) object

17. Step 3: both objects now identically charged and repel one another.

18. The Electroscope • made of two thin metal leaves attached to a metal rod with a knob at the top. - when the device is not charged, the leaves hang straight down. - when an electric charge is present, the leaves repel each other, spreading apart.

19. Electroscope electroscope simulations

20. 4 Ways to Charge Objects • #4: Induction: • Two neutral objects are in contact. • A third, charged object, is brought near the neutral objects to make them polarized. • The now polarized objects are separated making two oppositely charged objects.

21. Teacher Demo Draw a picture of what is happening to the charges in the aluminum cans.

22. Grounding phet - travolta

25. K Extensions

26. Conductors: metals, aqueous solutions of salts (i.e., ionic compounds dissolved in water), graphite, water, and the human body. Insulators: plastics, styrofoam, paper, rubber, glass, and dry air.

30. How a Van de Graaff Generator Works: Van de Graaff video

31. Sharing Charge via Conduction B B A A A B - + - - - - + + + + + + + + + - + + + - + - - + - - - - - - + - • A metal sphere (A) with a charge of +4 units is brought in contact with a metal sphere (B) with -2 units of charge, and the spheres are then separated. What is the charge on each sphere after separation? + - - + + + +4 -2 + + + +