1. Ch.20 - STATIC ELECTRICITY What is electrostatics? Electrostatic s is the study of electric charges that can be collected in one place.

2. ELECTRICITY Benjamin Franklin did the first real work – his famous kite experiment showed that lightning is similar to the sparks caused by friction. He defined electricity as a flow of positive charge

3. WHAT IS ELECTRICITY? Electricity is the movement or transfer of negative charge. Charge is a basic effect of the way each particle is put together. There are two types of charge: + & - (can also be neutral) Proton: positive charge Electron: negative charge Neutron: no charge

4. CHARGE Variable: q Unit: Coulomb (C) for an electron: -1.6 x 10 -19 C for a proton: +1.6 x 10 -19 C for a neutron: 0 C opposite charges attract like/same charges repel

5. CONDUCTIVE MATERIALS INSULATOR charges do not flow freely impedes electricity e.g. rubber, plastic CONDUCTOR charges flow freely allows electricity to flow through it e.g. metals NOTE: Wood is not a good conductor nor insulator.

6. Charge It! Materials –Plastic ruler –Tissue, copy, and cardstock paper –Scissors Objective –To observe how matter can be affected by electric charges. Procedures –Obtain materials. –Cut tissue paper into small pieces (1 cm 2 ). –Rub ruler through hair or on clothing. –Slowly lower it near the paper. –Record observations. –Touch the ruler with your other hand and lower to the paper again. –Record observations.

7. COULOMB’S LAW q 1 q 2 F = K r 2 q1q1 q2q2 r

8. Coulomb’s Law The force (F) between two charges is equal to Coulomb’s constant (K), times the product of the two charges (q A, q B ), divided by the square of the distance between them (r 2 ). K = 9.0 x 10 9 N m 2 /C 2

9. Coulomb’s Law Practice Problems p552 #9, 10,12 9. -1.6 x 10 4 N 10. 3 x 10 -6 C 12. 0.068 N to right

10. STATIC ELECTRICITY By definition, a non-moving flow of electrons As unlikely as that sounds, we may experience this many times a day. Grounding – touching an object to Earth to eliminate excess charge. E.g. shuffling our feet, getting out of the car, doing laundry, using a microwave, and…LIGHTNING!

11. LIGHTNING The most impressive display of static electricity Clouds build up static electricity, and then discharge that to the ground Always seeks path of least resistance, usually tall, pointy objects http://www.youtube.com/wat ch?v=h-0gNl5f4BUhttp://www.youtube.com/wat ch?v=h-0gNl5f4BU

12. http://www.youtube.com/watch?v=vQ0_Lwa4H2ghttp://www.youtube.com/watch?v=b3x-8tj49ac

13. 42. 2F, F/4, F/9, 4F, 3F/4 44. 1x10 -8 N 45. -250 N 46. 0.30 m 47. 3.2x10 -19 C 48. 98 N, east 49. q A =5.2x10 -7 C, q B =1.5x10 -6 C 51. 18 N right, 42 N left HW ch20

14. ELECTRIC FIELDS

15. Representation of the effect of one charge on its environment Representation of the effect of two charges on each other E Field lines are always drawn perpendicular to the surface and may never cross each other variable: E units: N/C

16. ELECTRIC FIELD E = F / q E : Electric Field (N/C) F : Coulomb Force (N) q : test charge (C)

17. POTENTIAL DIFFERENCE V = E d V : potential difference [voltage] (Volts) E : Electric Field (N/C) d : distance apart (m) ∆V = W/q` ∆V: difference in electrical potential (V) W: work (J) q`: test charge (C)

18. CAPACITORS C = q / V C : capacitance (Farads) q : charge (C) V : voltage (Volts)

19. 76. 50 Volts 78. -7.2x10 -17 J 79. 100 C 80. 90 Volts 83. 150 Volts 84. 8x10 -19 C, 5 e - 85. 6.75x10 -10 C CH 21 HOMEWORK