Electrostatics Spring

1. Electrostatics Spring

2. Intro Physics Midterm Moved to Friday Intro Questions: Start a new section of intros • What is lightning? 2. Why does lightning occur? 3. Why does it not occur every time we have clouds?

3. Your Goal Today • In a paragraph: Explain charging by friction, induction, and conduction. All three can be seen in the interaction between the PVC Pipe, wool, and paper. Use these as examples in your explanation.

4. Intro • Charge up the PVC pipe by rubbing the pipe with wool. • What happens to the hole punched paper when you get the charged PVC pipe close without touching? • Keep your area clean: Replace hole punches on the plate when done with the intro

6. Section 1: Intro to Static Electricity

7. Define Electrostatics • Electrostatics- Physics that deals with the attractions and repulsions of electrical charges not dependent on their motion. (Electricity at rest)

8. Electrical forces arise from charged particles in the atoms. • What are the charged particles called? - ____________ + ____________

9. Electrical forces arise from charged particles in the atoms. Proton (+) Electron (-)

10. Define charge • Charge- The fundamental electrical property to which mutual attractions or repulsions between electrons or protons is attributed. • Neutral atoms contain equal numbers of positive protons and negative electrons. (net 0 charge)

11. Only the electrons move to create unbalanced charges.

12. When atoms lose electrons they become positively charged ions. 11p 12 n 11p 12 n Becomes Neutral Sodium (Na) 11 protons(+) and 11 electrons(-) Positive Sodium Ion (Na+) 11 protons(+) and 10 electrons(-)

14. When atoms gain electrons they become negatively charged ions. 17 p 18 n 17 p 18 n Becomes Neutral Chlorine (Cl) 17 protons(+) and 17 electrons(-) Negative Chlorine Ion (Cl-) 17 protons(+) and 18 electrons(-)

15. Electrical charges are conserved! • When one atom becomes a positive ion another one/few must have accepted those electrons and become equally negative • Ex sodium is +1 because it gave its extra electron to chlorine 17 p 18 n 11p 12 n Becomes Negative Chlorine Ion (Cl-) 17 protons(+) and 18 electrons(-) Becomes Positive Sodium Ion (Na+) 11 protons(+) and 10 electrons(-)

16. Interaction between charges • Like charges repel and opposite charges attract.

17. Define static electricity • Static Electricity - Electricity at rest • Electric charges that can be confined to an object I hate static electricity

18. Some materials have a greater affinity for electrons • Greater affinity for e- : stick to electrons more and tend to gain electrons becoming negative • Less affinity for e- : don’t hold electrons as tight and are more likely to loose electrons become positive

19. Friction can cause charge separation • Electrons are stripped from one material and added to the other when rubbed together

20. Charging by friction • A wool cloth does not have much affinity for electrons. • Becomes Positive • PVC becomes negative + + + + + + + + + + + + + + + + + + + + + + + + - - - - -

21. Activity 1 List some examples of charging by friction When have you noticed static electricity or attraction of one object to another • Static cling from dryer (cotton socks w/ nylon pants) • Balloon rubbed in hair • Walking on carpet

22. Attraction for electrons

23. Question Set 1 1. A girl pulls a wool cap off her head. What charge will be produced: • on her hair? • on her cap? 2. Which will produce the most static cling with a cotton t-shirt in a dryer. Wool socks or a nylon nightgown? 3. Can there be static cling if only cotton items are placed in a dryer? 4. Predict the charges on the underlined objects: • A rubber rod rubbed with fur • A glass test tube rubbed with silk • A PVC pipe rubbed with nylon

24. Question Set 1 1. A girl pulls a wool cap off her head. What charge will be produced: • on her hair? positive • on her cap? negative 2. Which will produce the most static cling with a cotton t-shirt in a dryer,wool socks or a nylon nightgown? 3. Can there be static cling if only cotton items are placed in a dryer? No 4. Predict the charges on the underlined objects: • A rubber rod rubbed with fur negative • A glass test tube rubbed with silk positive • A PVC pipe rubbed with nylon negative

25. Conductor • Material through which electrons move freely • Examples (gold, silver, copper, and aluminum) • The general rule is that good thermo conductors are good electric conductors

26. Metals tend to share electrons in electron clouds • electrons are free to move around making them better conductors.

27. Electrical Insulator Electrical Conductor

28. Insulator • Material through which electrons do not freely move • Examples: rubber, paper, plastic, air

29. Grounding • Removing a static charge by producing a path to the ground • Electrons move from a negatively charged objects to the ground until the object is neutral • Electrons move from ground to neutralize positively charged objects • The earth both accepts and gives electrons while remaining overall neutral Grounding wand for Van De Graaff generator

30. grounding It’s easy to ground conductors since electrons transfer readily It’s hard to ground insulators since charges don’t move away easily

31. Section 2: Charging Objects Three Ways of putting a charge on an object • Friction • Induction • Conduction

32. 1. Charging by Friction • Charging by rubbing objects that have different affinities for electrons together + + + + + + + + + + + + + + + + + + + + + + + + - - - - -

33. Induction (charging without contact) • Bring a charged object (rod) close to a neutral one (ball) without contact - - - - - + + + + + + + + + - - - - - - - - -

34. Induction (charging without contact) • Bring a charged object (rod) close to a neutral one (ball) without contact • The electrons in the ball will be repelled leaving a positive side - - - - - + + + + + + + + + - - - - - - - - - + + + + + + + + + - - - - - - - - -

35. Induction (charging without contact) • Bring a charged object (rod) close to a neutral one (ball) without contact • The electrons in the ball will be repelled leaving a positive side • The now positive sided ball with be attracted to the negative rod - - - - - + + + + + + + + + - - - - - - - - -

36. Induction (charging without contact) • Induction is only a temporary change without contact therefore electrons are not transferred • The charge induced is opposite • Take away the rod and a neutral charge will return - - - - - + + + + + + + + + - - - - - - - - - + + + + + + + + + - - - - - - - - -

37. Conduction (charging with contact) • Conduction is a more permanent changewith contact; electrons are transferred and then isolated. • Charge conducted is the same • After conduction the ball and rod will repel each other - - - - - - - - - - - - - - + + + + + + + + + - - - - - - - - -

38. Make this table in your notes

39. Question Set 2 • Which of these, conduction or induction, produces a charge that is the same? Conduction • Which of these, conduction or induction, produces a permanent charge? Conduction • Which of these , conduction or induction, occurs without contact? Induction

40. Question Set 3 • Conduction occurs with ________ and the __________ charge is acquired. • no contact, same • contact, same • no contact, opposite • contact, opposite • Induction occurs with ________ and the __________ charge is acquired. • no contact, same • contact, same • no contact, opposite • contact, opposite

42. 3. Which of the following means of charging an object is more permanent? • Conduction • Induction

43. 4. What is grounding?

44. 5. What do you need for grounding to occur?

45. 6. Which of the following are true? • A positive charge attracts a negative charge • A negative charge attracts a positive charge • Same charges repel each other • All of the above

46. Section 3: Coulomb’s Law Intro questions • What is induction? • What is conduction? • How are they similar? • How are they different?

47. Electric Charge • Symbol is Q or q • The MKS unit is the coulomb (C) • 1 C = the charge on 6.25 x 1018 electrons Extra info to help you with problems • 1 electron = 1.60 x 10-19 C • A coulomb is a huge charge. Static charge is usually stated in µC which is 1x10-6 C.

48. Magnitude of force 3 factors affecting the magnitude of the force between two charged objects: • Charge on the objects • Distance between objects • Material separating objects

49. Coulomb’s Law • F: electrical force • Q1: charge 1 • Q2: charge 2 • d: distance between charges • k: constant depending on materials separating objects • For air, k = 9.0 x 109 N·m2/C2

50. Question Set 4 • How are charge and electrical force proportional? (directly or inversely) • How is electrical force proportional to distance? (directly or inversely) • The better the insulator between the objects, the ______ the value of “k”. • If the charge on each object is doubled and the distance between them is quadrupled, how will the force be affected?