1. Electrostatics

2. KWL – It’s Electric! Make a 3 column chart in your notebook and title the three columns K, W, L: K (know) Write everything you know about electricity here. W (want) Write anything you want to learn about electricity here. L (learned) Leave Blank for Now! Later you will write everything that you learned from your study in electricity!

3. Electrostatics Electrostatics is the study of electrical charges at rest. Did you know?: The force due to the charges of one proton and one electron are on the scale of 10 40 times bigger than the force due to gravity between these particles!

4. Static Electricity Continued… Side Note: The word electricity comes from the Greek word, elektron, which means “amber.” The Greeks found that if you rub amber with cloth, and bring it near dust or small leaves, it would attract these things.

5. Static Electricity Electrons be added or taken away from an atom when a strong enough force is applied. (Friction can do the trick!) Electrons can be added or taken away from an atom when a strong enough force is applied. (Friction can do the trick!) Once electrons are either lost or gained by an object. The object is said to be “charged.” Unlike charges attract; like charges repel. Benjamin Franklin was the first to distinguish charge as either + or -

6. Where do the Charges Come From? Electrons can be pulled from their orbits in an atom. Normally, there is the same number of electrons as protons in each atom. Ions are atoms that do not have equal numbers of electrons and proton.

7. The Atom The nucleus, made up of protons and neutrons, is orbited by electrons. The electrons on the outermost shell can be pulled off of the atom if the proper amount of force is applied.

8. The Parts of the Atom Summary of Subatomic Particles: ProtonNeutronElectron In nucleus Tightly Bound Positive Charge Massive In nucleus Tightly Bound No Charge Massive Outside nucleus Weakly Bound Negative Charge Not very massive

9. https://www.youtube.com/watch?v=xqNSQ 3OQMGI https://www.youtube.com/watch?v=xqNSQ 3OQMGI https://www.youtube.com/watch?v=q2QY6 w93-_I https://www.youtube.com/watch?v=q2QY6 w93-_I

10. Charges Charge is conserved, meaning the total amount of charge in the universe is constant. Therefore => “The net amount of electric charge in any process is zero.” Law of Conservation of Electric Charge

11. Question 1 Jean Yuss makes the following observations: Object CObject DObject EObject F attracts Brepels Cattracts D repels F attracts A Jean knows that object A is negatively charged. What are the charges on objects C, D, E, and F? Jean Yuss, knows… Explain how...

12. Conductors Conductors are materials which allow electrons to flow freely from atom to atom. A conductor will allow charge to spread out equally across the entire surface of the object.

13. Conductors

14. Insulators In contrast to conductors, insulators are materials which impede the free flow of electrons from atom to atom.

15. Semiconductors A semiconductor is a material that behaves like both a conductor and an insulator. At room temp. S.C.’s conduct slightly more than an insulator but less than a conductor. At very low temp. S.C.’s behave as insulators. At high temp. or under direct light, S.C.’s act as great conductors. Source: www.siliconfareast.com/whatissemicon.htm

16. Weekly HW. Due 3-19-10 Section Review Questions Pg. 563 (ALL) & Practice Problems A on Pg. 566

17. Electrical Forces Electrical Forces are forces due to charged particles or objects.

18. Coulomb’s Law F e = k q1.q2q1.q2 d2d2 Where: F e = the electrical force k = constant = 9x10 9 N. m 2 /C 2 q 1 = the charge on object 1 q 2 = the charge on object 2 d = the distance between the objects or charges

19. Charge! Note that in this equation the k is a very large constant! Electric forces are strong! Coulombs: SI Unit of Charge Also note, the charge of an electron is: e or q e = -1.6x10 -19 C e or q e = -1.6x10 -19 C What is the charge of 1 proton? q p = +1.6x10 -19 Coulombs

20. Question 1 Two charged objects have a repulsive force of 0.80 N. If the distance separating the objects is doubled, then what happens the force? A. It becomes less B. It increases C. It remains the same Answer: It Becomes Less!.2 N

21. Question 2 Determine the electrical force of attraction between two balloons if one is charged with 6.0 x 10 -7 C of charge and the other is charged with -6.0 x 10 -7 C. The balloons are measured to be a distance of 0.50 m apart.

22. Solution Step 1: Identify known values in variable form: q 1 = -6.0 x 10 -7 C q 2 = +6.0 x 10 -7 C d = 0.50 m. Step 2: Identify what you are trying to find. F = ??? Step 3: Substitute and solve. F = (9x10 9 )(-6.0 x 10 -7 )(+6.0 x 10 -7 ) 0.50 2 Answer: -0.0130 N

23. Question 3 If a charge on one sphere +3.0 x 10 -8 C and another charge of +2.0 x 10 -8 C is brought nearby, what is the strength of the electrical force when they are a distance of 0.6 m apart? Draw a picture that includes the force vectors for this situation. Be sure to indicate proper direction.

24. Solution Step 1: Identify known values in variable form. q 1 = +3 x 10 -8 C q 1 = +3 x 10 -8 C q 2 = +2 x 10 -8 C q 2 = +2 x 10 -8 C d = 0.6 m d = 0.6 m Step 2: Identify what you are trying to find F = ??? Step 3: Substitute and solve F = (9x10 9 )(3x10 -8 )(2x10 -8 ).6 2 Answer: 1.5x10 -5 N

25. Coulomb’s Law – Note on the Sign of the Force When you use coulomb’s law the sign of the force will indicate if it is an attractive or a repulsive force. If F is + Then the charges Repel If F is + Then the charges Repel If F is - Then the charges Attract If F is - Then the charges Attract What does the Sign of a Force Vector Normally Indicate??? Answer: Direction

26. Challenge Problem

27. Charging by Induction Another Method for charging is induction. Induction only occurs in conductors because electrons have to be free to move.

28. Lightning (a.k.a. charging by induction!!) _ + _ _ + + Collisions produce charged rain particles. The heavier particles are (-) because they have more electrons. Thus they sit near the bottom of the cloud and the lighter particles (+) sit near the top. Negative charge in the clouds induces a positive charge on the earth below. “Stepped Leader” Negatively charged electrons begin zigzagging downward. Attraction As the “stepped leader” nears the ground, it draws a “streamer” of positive charge upward. Flowing Charge As the leader and the streamer come together, powerful electric current begins flowing Contact! Intense wave of positive charge, a “return stroke,” travels upward at 10 8 m/s

29. Charge Polarization Charge Polarization Occurs in Insulators and not in conductors. Occurs in Insulators and not in conductors. Happens when an object is brought near a strong charge. Happens when an object is brought near a strong charge. Individual atoms line up so that they all have their + side and – side facing the same way. Individual atoms line up so that they all have their + side and – side facing the same way.

30. Electric Fields An Electric Field surrounds any particle that has charge. An electrical field exists because electric force will act on any charged particle nearby. “Stinky Analogy!!! “Stinky Analogy!!! E = F q Where q is the test charge.

31. Electric Field Lines Electric field lines are shown moving out of positive particles and into negative particles. More lines, closer together indicate strong fields! Less lines spread further apart represent weaker fields.

32. Electric Field Hockey..\..\..\Desktop\electric-hockey.jar

33. Review: Potential Energy Review Questions: Review Questions: 1. What is work? 2. What is gravitational potential energy?

34. Work and Potential Energy The amount of work done on a particle to move it through an electric field is equal to the Potential Energy gained or lost. Remember Conservation of Energy! Recall lifting a rock of the ground.

35. Electrical Potential Energy A charged object has Electrical Potential Energy because of its location in an electric field!!!! A charged object has Electrical Potential Energy because of its location in an electric field!!!! To move a charge in an electric field against its natural direction of motion would require work.

36. Electrical Potential Energy Which Positive Test Charge has more Electric Potential Energy? + + q1 q2 Charges always want to be at the lowest potential energy possible.

37. Electric Potential We know that Electrical Fields exist, even when no test charge is present. (remember the stinky analogy!) Using similar logic, we can reason that different P.E. levels exists around a charge at different locations in space, regardless of the size of the test charge used. Electric Potential or just Potential is simply Electric Potential Energy divided by test charge. (this is also called voltage.) V = PE elec. / q V = Electric Potential at some point in space

38. Potential Difference Only differences in electrical potential are important!!! If point ahas high potential (V a ), and point b has low potential (V b ), then a positive test charge will move from a towards b. If point a has high potential (V a ), and point b has low potential (V b ), then a positive test charge will move from a towards b. A negative test charge will do the opposite. If there is no difference in electric potential, then a test charge will not move if released!

39. Electric Potential And Potential Energy V = PE elec. / q And by algebra: PE = q x V  PE = PE b – PE a = q x (V ba ) + + q1 q2 V a V b This also equals the work done to move the particle from A to B.

40. Relationship between E and V For a constant Electric Field, E, the electric potential between two points is easily discovered: V ba = E. d Where d is the distance between the charges.

41. Equations for Electrical Force, E Field, Electric Potential E = k. Q r 2 These equations only apply when a point charge (Q) is responsible for creating the electric field. V = k. Q r F = k. q. Q r 2 SCALAR! Not a VECTOR!