1. Electrostatics

2. History The word electricity comes from the Greek elektron which means “amber”. The “amber effect” is what we call static electricity.

3. History Ben Franklin made the arbitrary choice of calling one of the demo situations positive and one negative. He also argued that when a certain amount of charge is produced on one body, an equal amount of the opposite charge is produced on the other body…

4. Charge Concepts Opposite charges attract, like charges repel. Law of Conservation of Charge: –The net amount of electric charge produced in any process is zero. t hanks Ben!!! Symbol: q, Q Unit: C, Coulomb

5. Elementary Particles ParticleCharge, (C)Mass, (kg) electron-1.6x10 -19 9.109x10 -31 proton+1.6x10 -19 1.673x10 -27 neutron01.675x10 -27 If an object has a… + charge  it has less electrons than normal - charge  it has more electrons than normal

6. Ions and Polarity If an atom loses or gains valence electrons to become + or -, that atom is now called an ion. If a molecule, such as H 2 O, has a net positive charge on one side and negative charge on the other it is said to be polar

7. Why does… Chemistry work? Physics!!! The electrostatic forces between ions (within molecules) form bonds called ionic bonds…all bonds are ionic; others, like covalent, are to a much lesser degree so that you can ignore the ionic properties of that type of bond.

9. Why does… Biology work? Physics!!! The intermolecular electrostatic forces between polar molecules make such things as the DNA double helix possible.

10. Types of materials 1.Conductor: a material that transfers charge easily (ex. Metals). 2.Insulator: a material that does not transfer charge easily (ex. Nonmetals) 3.Semiconductors: somewhere between 1 & 2 (ex. Silicon, carbon, germanium). 4.Superconductors: some metals become perfect conductors below certain temperatures

11. Ways to Charge By Friction: two objects rubbed against each other may cause a transfer of charge from one to another (triboelectrification) Result: each object has a net charge which is equal and opposite to the other By Conduction: contact occurs between charged object and neutral object. Result: two objects with same charge By induction: no contact occurs between charged object and neutral object. Result: two objects with opposite charge Credit Card: You may use Visa, Master Card, or American Express Result: Debt from high interest rates

12. Charging by Friction Materials have different affinities for electrons. A triboelectric series rates this relative affinity. POSITIVE Rabbit's fur Glass Mica Nylon Wool Cat's fur Silk Paper Cotton Wood Lucite Wax Amber Polystyrene Polyethylene Rubber ballon Sulfur Celluloid Hard Rubber Vinylite Saran Wrap NEGATIVE When insulators are rubbed together, one gives up electrons and becomes positively charged, while the other gains electrons and becomes negatively charged. plastic foodwrap that sticks to a container sweater pulled over your head that sparks laundry from the dryer that clings Common examples of charging by friction: A material will give up electrons to another material below it on a triboelectric series. small shocks from a doorknob after walking on carpet with rubber-soled shoes balloon rubbed with hair sticks that to a wall click for applet

13. Charging by Conduction When a charged conductor makes contact with a neutral conductor there is a transfer of charge. Electrons are transferred from the rod to the ball, leaving them both negatively charged. Electrons are transferred from the ball to the rod, leaving them both positively charged. Remember, only electrons are free to move in solids. CHARGING NEGATIVELYCHARGING POSITIVELY Notice that the original charged object loses some charge.

14. Conduction

15. Charging by Induction Step 1. A charged rod is brought near an isolated conductor. The influence of the charge object polarizes the conductor but does not yet charge it. Step 2. The conductor is grounded to the Earth, allowing charge to flow out between it and the Earth. Induction uses the influence of one charged object to “coerce” charge flow.

16. Step 3. The ground is removed while the charge rod is still nearby the conductor. Step 4. The rod is removed and the conductor is now charge (opposite of rod). Charging by Induction (cont.) An object charged by induction has the opposite sign of the influencing body. Notice that the original charged object does not lose charge.

17. Induction Polarization

18. Conduction or Induction A B

19. Lightning Becomes very “negative” Becomes very “positive”

20. Lightning (1)

21. Lightning (2)

22. Lightning (3)

23. Lightning (4)

24. Lightning (5)

25. Lightning (6)

26. Lightning Video Lightning Video compliments of Tom A. Warner, ztresearch.com 640x480 pixels 7,200 images per second 0.15 seconds recording time Visual aspects: -stepped leaders -dart leaders -return strokes -continuing current

27. Lightning Rod Simulator Lightning striking the Empire State Building

28. Van de Graaff electrostatic generator: simulates lightning from cloud to ground

29. Electric Forces and Electric Fields CHARLES COULOMB (1736-1806) MICHAEL FARADAY (1791-1867)

30. Electric Force AKA: Coulomb’s Law Using a torsion balance, Coulomb found that: the electric force between two charges is proportional to the product of the two charges and inversely proportional to the square of the distance between the charges.

31. Electric Force

32. q  charge, C r  distance between charges, m F E  Electric Force, N  VECTOR k c  coulomb constant, 8.99x10 9 Nm 2 /C 2

33. The Electrostatic Force EXAMPLE 1 - Find the force between these two charges EXAMPLE 2 - Find the net force on the left charge

34. Electric Field The electric force is a field force, it applies force without touching (like the gravitational force) In the region around a charged object, an Electric Field is said to exist

35. Electric Field Rules for Drawing Electric Field Lines 1.The lines must originate on a positive charge (or infinity) and end on a negative charge (or infinity). 2.The number of lines drawn leaving a positive charge or approaching a negative charge is proportional to the magnitude of the charge. 3.No two field lines can cross each other. 4.The line must be perpendicular to the surface of the charge

41. Electric Field E  electric field strength, N/C  VECTOR q 0  + test charge, C q  charge producing field, C r  distance between charges, m F E  Electric Force, N  VECTOR k c  coulomb constant, 8.99x10 9 Nm 2 /C 2

42. E-Field vs g-field

43. Electric Field Strength DEFINITION OF GRAVITATIONAL FIELD DEFINITION OF ELECTRIC FIELD Field Theory Visualizes Force At A Distance SI unit of electric fieldElectric field is a vector quantity q 0 is a small, positive test charge click for applet

44. Van der Graff Generator

45. When no net motion of charge occurs within a conductor, the conductor is said to be in electrostatic equilibrium There are four properties to consider when looking at conductors Conductors in Electrostatic Equilibrium

46. Property 1 The electric field is zero everywhere inside the conducting material –Consider if this were not true if there were an electric field inside the conductor, the free charge there would move and there would be a flow of charge If there were a movement of charge, the conductor would not be in equilibrium

47. Property 2 Any excess charge on an isolated conductor resides entirely on its surface –If some excess of charge could be placed inside the conductor, the repulsive forces would push them as far apart as possible, causing them to migrate to the surface

48. Property 3 The electric field just outside a charged conductor is perpendicular to the conductor’s surface –Consider what would happen if this was not true The component along the surface would cause the charge to move It would not be in equilibrium

49. Property 4 On an irregularly shaped conductor, the charge accumulates at locations where the radius of curvature of the surface is smallest (that is, at sharp points)

50. Conductors in Electrostatic Equilibrium 1.The electric field is zero everywhere inside a conductor. 2.Any excess charge on an isolated conductor resides entirely on the outside surface of the conductor. 3.The electric field just outside the charged conductor is perpendicular to the conductor’s surface. 4.On an irregularly shaped conductor, charge tends to accumulate where the radius of curvature is the smallest, i.e. AT SHARP POINTS.

51. E=0 Otherwise charges would be moved around (Not equilibrium) Charge resides along the surface => Charges try to get as far away as possible Perpendicular otherwise there would be a force acting on the charges along the surface Charge accumulates at smallest curvature

52. Electric Potential Difference (a.k.a. Voltage, Potential Difference) The difference of potential between two points is defined as the work done to move a charge from a point of lower potential to a point of higher potential

53. Potential Difference Where: V is the difference in potential between two points W is the work done in moving a charge in Joules q is the charge being moved in coulombs Units:

54. Electronvolts (eV) The Joule is a large unit of energy…much too large a unit to use when moving elementary charges around. The amount of work done to move a single elementary charge across a potential difference of one volt is called an electronvolt