Pre AP Physics

1. STATIC ELECTRICITY Pre AP Physics

2. STATIC ELECTRICITY • Electrostatic – the study of electrical charges that can be collected and held in one area. • They flow in no particular direction (trapped in a body)

3. Electricity of the Atom • They are ordinarily neutral in charge • # of protons = # of electrons • Neutrons = no charge • Protons = + 1 charge • Electrons = -1 charge

4. The actual charge of an electron -1.60217657 X 10-19 coulombs

5. Little History: Ben Franklin • Proved lightning was static electricity • Invented lightning rod • Built a static electricity generator • Coined the terms positive and negative for electrical charge

6. Charged objects • Atoms become charged by gaining or losingelectrons • An object that exhibits electrical interaction after rubbing is said to be charged

7. Rules of Attraction Opposite will attract Only the electrons will move Like will repel Protons will move but they don’t leave the nucleus.

8. Interaction between a charged object and a neutral object: • Any charged object (positive or negative) will have an attraction interaction with a neutral object.

9. Why are protons never lost or gained? • Protons are held in the nucleus by the strongest forces in the universe.

10. Ions • Are electrically charged particles • Charge is unbalanced • Negative Charge # e > # p • Positive charge # p > # e

11. Neutral State • Charged objects will eventually return to their NEUTRAL state • What/How does this happen? • The charge “leaks off” onto the water molecules in the air. • On humid/rain days it would be difficult to hold a charge for long.

12. Electro-negativity + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - Relative electro-negativity ranking for some common materials from electron donating materials (+, glass) to electron accepting materials (-, Teflon) • Glass • Human Hair • Nylon • Silk • Fur • Aluminum • Paper • Cotton • Copper • Rubber • PVC • Teflon

13. Grounded - neutral • Charged objects lose their charge when grounded. 

14. "What is thebottom prong of a plug called?" • The bottom prong of a plug is called the ground. • It discharges any excess charge that may develop in an electrical device

15. When grounded: • Negatively charged objects • .... Lose electrons and become neutral • Positively charged objects • ... Gain electrons and become neutral

16. Electroscope • Used to test the presence of a charged object.

17. If no charge is present, leaves point straight down.

18. Leaves separate when charge is present.

19. Where do charges come from? Rubbing materials does NOT create electric charges. It just transfers electrons from one material to the other.

20. Transfer of charge • Charge can be transferred between neutral objects by FRICTION. • Ex: Rubber rod rubbed with fur or wool will cause electrons to transfer to the rod • Rubber Rod gains electrons and becomes negative • Fur/wool loses electrons and becomes positive

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27. - + - + - + - - + - + + - - + - + + - +

28. Conduction • Charging by contact – direct touching • EX: Conduction with a negative rod

29. How do the electrons flow during conduction? • When a negative charged rod comes in contact with the knob the electrons flow into the electroscope – charge negative • When a postive charged rod comes in contact with the knob the electrons flow into the rod – charge positive

30. Charging by Induction

31. Charging by Induction

32. - - - - - - - + + + + + - - - - - Induction: The production of a charge in an uncharged body by bringing a charged object close to it When negatively charged rod is put near a metal can... electrons of the can are pushedaway from the rod. induced charges  top of the can: positive attraction buttom of the can: negative attraction > repulsion metal can repulsion

33. - - - - - - - – – – – – – – – + + + + + + + + Attraction of uncharged objects Similarly, when charged rod is close to paper scrap... molecules of paper align.  attraction between the rod and + charge > repulsion between the rod and - charge. attraction paper repulsion

34. Electricity, Height, and Women https://www.youtube.com/watch?v=FGoaXZwFlJ4&nohtml5=False

35. Static Discharge Human body can not feel less than 2,000 volts of static discharge Static charge built up by scuffing shoes on a carpet can exceed 20,000 volts!

36. Lightning

37. What causes lightning? • You need cold air and warm air. • It is a discharge of the static electricity that builds up in cloud in certain weather conditions. • Usually when the ground is warm and the air is humid.

38. Interesting facts • How hot is a lightning bolt? Only about 54,000 degrees Fahrenheit — roughly five times hotter than the surface of the sun! • Lightning flashes more than 3 million times a day worldwide — that’s about 40 times a second. Not all those flashes hit the ground — some happen between or inside clouds. • An average lightning bolt can release enough energy to operate a 100-watt light bulb for more than three months straight (about 250 kilowatt-hours of energy). • Lightning starts in cumulonimbus clouds — aka thunderheads — which have a positive charge up top and a negative charge below. We don’t know how the charges start, but water droplets and ice crystals carry them.

39. Lightning • Head straight to your car • Move to a lower location

40. Electric Fields • We visualize the field by drawing the field lines • Lines point in the same direction as the field. • Density of lines gives the magnitude of the field. • Lines begin on + charges; end on – charges.

41. Field Lines • Point direction a + charge would move • More lines = stronger field

43. Two positive charges..

44. A new force… • Electric force • Between 2 charged objects • Depends on distance and amt. of charge

45. Coulomb’s Law qAqB K F = d2 K = 9 x 109 N·m2/C2

46. Coulomb’s Law • Units • Charge - coulomb (C) • Force – Newtons (N) • Distance – meter (m) • Electric force is a vector

47. Van de Graaff Generator • The globe of the generator builds up excess electrons through conduction. • The built electrons are repelling since they are like charges and we know that like charges repel so they are spread out as much as possible. • The charges are spread out because the globe is a conductor, unlike electrons that are rubbed onto the balloon, which stay in the general area where you rub the balloon.