Static Electricity

1. Static Electricity

2. While waiting for the bell to ring, • Pick up note taking guide and get out lab from yesterday. • On the back of the note taking guide, answer the following question: Which force is stronger, gravitational or electrostatic? (Use the observations you made during yesterday’s lab to support your position.)

3. Charged Objects • Electrostatics is the study of electrical charges that can be collected and held in one place. • Electrical charges exist within atoms 1. electrons are negatively charged particles 2. protons are positively charged particles 3. neutrons are particles having no charge. • If the positive charge of the nucleus (protons) balances the negative charge of the surrounding electrons, the substance is neutral.

4. Separation of Charges • With the addition of energy, the outer electrons can be removed from atoms. • An atom missing electrons has an overall positive charge. • The freed electrons can become attached to other atoms resulting in negatively charged objects. • In lab yesterday when the wool was rubbed against the plastic, the electrons from the wool were transferred to the plastic. The wool was positively charged and the plastic was negatively charged. Glass will also become positively charged when rubbed against another material.

5. Behavior of charged particles • Objects having opposite charges attract each other. • Objects having the same charge repel each other.

6. 10 ___ are negatively charged particles. • Electrons • Neutrons • Positrons • Protons

7. 10 The charge on the nucleus is ____. • negative • neutral • positive

8. 10 Atoms are neutral when the number of protons and ____ are equal. • electrons • neutrons • positrons

9. 10 With the addition of energy, the ___ can be removed from atoms. • electrons • neutrons • protons

10. 10 An atom missing electrons has a ___ charge. • negative • positive

11. 10 Objects having like charges ___ each other. • attract • repel • have no affect

12. Conductors and Insulators • Materials through which charges will not easily move are called electrical insulators. • Charges placed on an insulator will remain where they are placed. • Examples include glass, dry wood, plastics, cloth, and dry air. • Materials that allow electrons to move about easily are conductors. • Charges placed on a conductor will spread over the entire surface. • Examples include metals and plasma.

13. 10 Plastic is an example of a(n) ___. • conductor • insulator

14. 10 ___ is an example of a conductor. • Cloth • Copper • Glass • Wood

15. Air can become a conductor when it is 10 • dry • plasma • discharged • wet

16. Forces on Charged Bodies • There are two kinds of electrical charges, positive and negative. • Charges exert a force over a distance. • The force is stronger when the charges are brought close together. • Like charges repel; opposite charges attract.

17. Coulomb’s Law • Coulomb’s Law states that the magnitude of the force between two charged objects (qA and qB), separated by a distance d, is proportional to the magnitude of the charges and inversely proportional to the square of the distance. • F = K [(qAqB)/d2] K=9.0x109 Nm2/C2 • The unit of charge is the coulomb (C) • One coulomb is the charge of 6.25x1018 electrons or protons. • One electron has a charge of how many coulombs?

18. Coulomb’s Law • Electric force, like all forces, is a vector quantity. • The Coulomb’s Law equation gives only the magnitude of the force. • To determine a direction, draw a diagram and interpret interaction between charges.

19. Transfer of Charges • When a negatively charged object touches another object, the electrons are transferred. This is called charging by conduction.

22. Charging by Induction • When a negatively charged object is brought close to one of two identical metal spheres that are touching, electrons from the first sphere will be forced onto the sphere farther from the object and will make it negatively charged. The closer sphere is now positively charged. If the spheres are separated while the charged object remains nearby, each sphere will have a charge. This is called charging by induction.

25. 10 How would the electrical force change if the distance between the two charges was increased? • The force would increase. • The force would decrease. • The force would remain the same.

26. 10 Charging a neutral object by direct contact with a charged body is called charging by • conduction • induction

27. 10 A neutral object that becomes charged without touching it to a charged object has been charged by • conduction • induction

28. 10 Yesterday in lab, the plastic tube became charged by • conduction • induction

29. Grounding • A single object can also be charged by induction through grounding. • Grounding is the process of connecting a charged body to Earth to eliminate excess charge. • Earth is a very large sphere that can absorb great amounts of charge without becoming noticeably charged itself. • If a charged body is touched to Earth, almost any amount of charge can flow to Earth.

32. 10 A negatively charged ruler is brought near one end of another negatively charged ruler. If the ruler is grounded on the opposite end of the ruler, what charge is being pushed into the ground? • Negative • Positive • Neither

33. 10 If the ground from the previous problem is removed before the charged ruler, what charge will the remaining ruler have? • Negative • Positive • Neutral

34. What is Lightning? • http://www.youtube.com/watch?v=Q3Awp-3CxSU&p=9D298A092F31A45A

35. As moist air rises and cools, ___ occurs. 10 • Condensation • Evaporation • Freezing • Sublimation

36. Wind causes the water droplets to be in motion which results in collisions causing a loss of 10 • electrons • protons • neutrons

37. The top of the cloud will be ___ charged and the bottom of the cloud will be ___ charged. 10 • positively, positively • negatively, negatively • positively, negatively • negatively, positively

38. Build up of the charge at the bottom of the cloud repels the ___ at the surface of the Earth. 10 • Electrons • Protons • Neutrons

39. Lightning forms when the ___ jump to the ground. 10 • electrons • protons • neutrons

40. Lightning forms in an attempt to ___ the charge separation. 10 • build up • neutralize