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# 03-26-08 - Electricity (Day 1)

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### 03-26-08 - Electricity (Day 1)

1. 1. Static and Current Electricity
2. 2. Electrostatics the study of electrical charges at rest Electrodynamics the study of electrical charges in motion Two opposite types of charge exist, named positive and negative by Benjamin Franklin . Charge is a property of matter.
3. 3. Charged particles exist in atoms. Electrons are responsible for negative charge; protons for positive charge; neutrons have no charge. Small amounts of ordinary matter contain incredible amounts of subatomic particles!
4. 4. Conductor material that allows charges to move about easily Insulator material through which charges will not easily move Basic Law of Electrostatics Like charges repel; unlike charges attract Link link link
5. 5. Click here to view a simulation of the behavior of pith balls in the vicinity of charged rods.
6. 6. Click here to read about charging objects by friction. View a simulation of charging a balloon by rubbing it on your hair and then sticking it to a neutral wall here .
7. 7. charging a rod and electroscope positively and negatively by conduction and induction When charging by conduction , the rod touches the electroscope. The electroscope gets the same charge as the rod. When charging by induction , the rod does not touch the electroscope. The electroscope gets the opposite charge of the rod.
8. 8. Go here to view simulations of charging an electroscope.
9. 9. COULOMB’S LAW The force between two charged objects is directly proportional to the product of their charges and inversely proportional to their separation distance squared. link1
10. 10. In equation form: F  F is the force of attraction , measured in newtons , between charges q 1 and q 2 k k is the Universal Electrostatic Constant , equal to 9.00 x 10 9 N m 2 /C 2 q 1 q 2 q 1 and q 2 are the attracting charges , measured in coulombs d 2 d is the distance between the charges , and is measured in meters
11. 11. The SI unit of charge is the coulomb , named in honor of Charles Augustin Coulomb . 1 C = charge on 6.25 x 10 18 electrons (or protons) 1 e - = 1.60 x 10  19 C = elementary charge Electric force is a vector and must be treated as such.
12. 12. Example Problem <ul><li>What is the force on a +2.3 μ C charge that lies 3.7 m to the left of a -5.1 μ C charge? </li></ul><ul><li>Given </li></ul><ul><ul><ul><li>q 1 = +2.3 μ C = +2.3 x 10 -6 C d = 3.7 m </li></ul></ul></ul><ul><ul><ul><li>q 2 = -5.1 μ C = -5.1 x 10 -6 C k = 9 x10 9 N*m 2 /C 2 </li></ul></ul></ul><ul><ul><ul><li>F = ? </li></ul></ul></ul><ul><li>B.E. </li></ul><ul><ul><ul><li>F = kq 1 q 2 /d 2 </li></ul></ul></ul><ul><li>W.E. </li></ul><ul><ul><ul><li>F = (9 x10 9 N*m 2 /C 2 )*(+2.3 x 10 -6 C)*(-5.1 x 10 -6 C) </li></ul></ul></ul><ul><ul><ul><li> (3.7 m) 2 </li></ul></ul></ul><ul><li>Answer </li></ul><ul><ul><ul><li>F = -0.0077 N </li></ul></ul></ul><ul><ul><ul><li>(“-” means attraction) </li></ul></ul></ul>
13. 13. Example Problem <ul><li>How far is a +4.5 m C from a -8.2 mC if there is a force of 13 N between them? </li></ul><ul><li>Given </li></ul><ul><ul><ul><li>q 1 = +4.5 m C = +4.5 x 10 -3 C d = ? </li></ul></ul></ul><ul><ul><ul><li>q 2 = -8.2 mC = -8.2 x 10 -3 C k = 9 x10 9 N*m 2 /C 2 </li></ul></ul></ul><ul><ul><ul><li>F = 13 N </li></ul></ul></ul><ul><li>B.E. </li></ul><ul><ul><ul><li>F = kq 1 q 2 /d 2 </li></ul></ul></ul><ul><li>W.E. </li></ul><ul><ul><ul><li>13 N = (9 x10 9 N*m 2 /C 2 )*(+4.5 x 10 -3 C)*(-8.2 x 10 -3 C) </li></ul></ul></ul><ul><ul><ul><li> d 2 </li></ul></ul></ul><ul><ul><ul><li>Multiply both sides by d 2 , then divide both sides by 13 N </li></ul></ul></ul><ul><li>Answer </li></ul><ul><ul><ul><li>D = 160 m </li></ul></ul></ul>