build-up of electric charge on surface of objects

1. Static Electricity build-up of electric charge on surface of objects

2. Scalars- magnitude (or numerical value) alone example: 5 Vectors- both a magnitude and a direction example: 5 meters Are the following scalar or vector quantities?

3. Force as a Vector Quantity Has a magnitude and direction

4. Coulomb's Law Equation Q1 - quantity of charge on object 1 (in Coulombs) Q2 - quantity of charge on object 2 (in Coulombs) d - distance of separation between the two objects (in meters) k - Coulomb's law constant (in air, 9.0 x 109 N • m2 / C2)

5. Coulomb's Law Changing the Distance Between Charged Objects • What happens to the electrical force when the distance • between point charges is • Doubled • Halved • If the electrical force is 4 N when the distance is 2 m, what is the • Force when the distance between point charges is 4 m?

6. Coulomb's Law Changing the amount of charge q1 q2 • What happens to the electrical force when q1is • Doubled • Halved • If the electrical force is 4 N when q1 is +2 C, what is the • force when q1 is +4?

7. Coulomb's Law Force “-" or “+" Attractive Force Repulsive Force ("-" F value) ( "+" F value)

8. Coulomb's Law k = 9.0 x 109 N•m2/C2

9. Coulomb's Law k = 9.0 x 109 N•m2/C2

10. Coulomb's Law Felect = k • Q1 • Q2 / d2 Felect = (9.0 x 109 N•m2/C2) • (1.00 C) • (1.00 C) / (1.00 m)2 Felect = 9.0 x 109 N

11. Coulomb's Law 1 C = 10-6C k = 9.0 x 109 N•m2/C2

12. Coulomb's Law

13. Coulomb's Law Felect = k • Q1 • Q2 / d2 d2 • Felect = k • Q1 • Q2 d2 = k • Q1 • Q2 / Felect d = SQRT(k • Q1 • Q2) / Felect d = SQRT [(9.0 x 109 N•m2/C2) • (-8.21 x 10-6 C) • (+3.37 x 10-6 C) / (-0.0626 N)] d = Sqrt [ +3.98 m2 ] d = +1.99 m

14. Electric Field

15. Electric Field Action-at-a-distance forces are sometimes referred to as field forces.

16. Electric Field When placed within the electric field of the source charge, the test charge will experience an electric force - either attractive or repulsive. Electric field strength is force per charge on the test charge.

17. Electric Field For any given location, the arrows point in the direction of the electric field and their length is proportional to the strength of the electric field at that location. Note that the lengths of the arrows are longer when closer to the source charge and shorter when further from the source charge.

18. Electric Field easier to talk about field lines, always directed away from positive source http://www.youtube.com/watch?v=F1z5UaX96j8 (First 1:33, ignore the rest)

19. Rules for Drawing Electric Field Lines • Electric field lines always extend from a positively charged object to a negatively • charged object, from a positively charged object to infinity, or from infinity to a • negatively charged object. • Electric field lines are most dense around objects with the greatest amount of • charge. • At locations where electric field lines meet the surface of an object, the lines are • perpendicular to the surface. • Electric field lines never cross each other.

20. Electric Field (2 charges)

21. Electric Field Lines Two Positively Charged Objects Two Negatively Charged Objects Negatively and Positively Charged Object

22. Electric Field Lines

23. Electric Fields and Surface Curvature

24. Electric Field - Electric Fields Inside of Charged Conductors at Electrostatic Equilibrium is Zero - Conductors only have charge on surface Michael Faraday, 19th century physicist Faraday cage Any closed, conducting surface can serve as a Faraday's cage, shielding whatever it surrounds from the potentially damaging affects of electric fields. This principle of shielding is commonly utilized today as we protect delicate electrical equipment by enclosing them in metal cases.

25. Lightning Static Charge Buildup in the Clouds • Polarization of positive and negative charges within a storm cloud • (not quite understood) - • Frictional charging: Upwardly rising moisture collides with water droplets within the clouds. In the collisions, electrons are ripped off the rising droplets, causing a separation of negative electrons from a positively charged water droplet or a cluster of droplets. • Freezing process: Rising moisture/cooler frozen particles tend to cluster

26. Lightning Mechanics of a Lightning Strike 1) static charge buildup in a storm cloud 2) electric field surrounding the cloud becomes stronger 3) surrounding air becomes more conductive – plasma 4) lightning bolt step leader: excess electrons on the bottom of the cloud begin to go from conducting air to the ground, (up to 216000 mph) streamer: upward rising positive charge from Earth 5) thunder enormous and rapid flow of charge along lightning bolt heats the surrounding air, causing it to expand violently causing shockwave http://video.search.yahoo.com/search/video;_ylt=A2KLqITFhkpP_ycAP_j8w8QF;_ylu=X3oDMTBrOTlpOGs3BHNlYwNzZWFyY2gEdnRpZANWMTE2?p=lightning+how+it+works+physics&ei=utf-8&n=35&tnr=35 How lightning works - Discovery Channel

27. Lightning Rods Elevated lightning rod provides conductive pathway for charge to the Earth Attached by a thick copper cable to a grounding rod that is buried in the Earth below Prevents damage from occurring to the building Tip of the lightning rod does not need to be sharply pointed as Ben Franklin suggested Blunt-tipped lightning rods have been found to be more receptive to lightning strikes and thus provide a more likely path of discharge of a charged cloud