1. Day 93, Monday, 1 February, 2016 Capacitance Electric Fields Electric Potential Coulombs Millikan's Oil Drop Experiment Capacitors Coulomb’s Law

2. Static Charge Silk on glass+ Fur on plastic -

3. Number of charges measured in coulombs (C) The smallest charge itself is called  e One coulomb of charge contains 6.2 x 10 18 charges or 6.2 x 10 18 e That is +6.2 x 10 18 (protons) or -6.2 x 10 18 (electrons) in a coulomb One proton contains +1.602 x 10 -19 C of charge One electron ( e - ) contains -1.602 x 10 -19 C of charge

4. Conductors (charges move) In elevators people go to the walls. Everyone moves to the farthest possible point, so they are all around the walls. In conductors electrons distribute themselves around the surface. Electrons are free to move and stay as far apart as possible

5. Insulators (charges isolated) Insulators are also called dielectrics because the charges cannot move, so the atoms stretch. This leads to a negative side and a positive side.

6. Air breakdown voltage 3 million volts Sparks at much lower voltages

8. Electric field Electric field relates force on a test charge to the size of the test charge E = F/q’units N/C

9. Electric field lines Direction perpendicular to field Spacing indicates strength Positive charge lines go out Negative charge lines go in

12. Electric Fields near conductors

13. Electric Potential Electric potential (also called the electrostatic potential) at a point in space is potential energy divided by charge that is associated with a static electric field. It is a scalar quantity, typically measured in volts.

14. Electric Potential - Voltage Electric Potential Difference ∆V = W on q´ /q´ Volt1 V = 1 J/C

15. Coulomb 1 coulomb is the amount of electrical charge in 6.241506×10 18 electrons or other elementary charged particles The charge of one electron is equal to -1.6022×10 -19 C

16. Coulomb A coulomb is equal to 6.24150962915265 × 10 18 elementary charges An electron contains 1.60217649 x 10 -19 coulombs of negative charge - 1.60217649 x 10 -19 C A proton contains 1.60217649 x 10 -19 coulombs of positive charge + 1.60217649 x 10 -19 C

17. Millikan oil drop experiment – the mass of electron

18. Storing charge Capacitors C = q/∆V coulomb / volt = farad Named after Michael Faraday 2 conducting plates parallel to each other

21. Capacitors Start Run

22. Of tape and Gecko’s feet

23. The balance of positive and negative charges Coin ≈1 million coulombs negative charge 10 -9 unbalanced charge large force

24. Insert comb trick here

25. Coulomb’s Law F = k c q A q B d 2 k c = 8.99 x 10 9 Nm 2 /C 2 (Coulomb’s constant) C = 6.25 x 10 18 e - or p + (coulomb) 1/ 6.25 x 10 18 = 1.60 x 10 -19 C/e -

26. Coulomb’s Constant and Boltzmann’s Constant are different entities Coulomb’s Constant k e or k c It is 8.99 x 10 9 Nm 2 /C 2 Boltzmann’s Constant k or k b It is 1.3806488(13)×10 −23 J K −1 8.6173324(78)×10 −5 eV K −1 1.3806488(13)×10 −16 erg K −1

27. Coulomb’s Law Problem One charge of 2.0 C is 1.5 m away from a –3.0 C charge. Determine the force they exert on each other.

28. Coulomb’s Law Problem worked out F e = k c q 1 q 2 r 2 F e = (8.99 x 10 9 ) (2.0)(−3.0) 1.5 2 F e = 2.4 x 10 10 N (attractive)

29. Coulomb’s Law Problem # 2 Two balloons are charged with an identical quantity and type of charge: - 6.25 nC. They are held apart at a separation distance of 61.7 cm. Determine the magnitude of the electrical force of repulsion between them.

30. Problem # 2 Worked Out Q 1 = -6.25 nC = -6.25 x 10 -9 C Q 2 = -6.25 nC = -6.25 x 10 -9 C d = 61.7 cm = 0.617 m F elect = [k (Q1 Q2) ]/ d 2 F elect = [(9.0 x 10 9 )(6.25 x 10 -9 )(6.25 x 10 -9 )] / (0.617 ) 2 F elect = 9.23 x 10 -7 N

31. Credits Gecko Feet Comb Trick Photo science-notebook.com/.../comb-paper.jpg www.andrew.cmu.edu/user/gshah/gecko_foot.jpg

32. Credits Capacitor diagram www.yourdictionary Capacitor photos (big green) Profesanxenxo.iespano.es Capacitor photos (little yellow) www.play-hooky.com

33. Credits Coulomb’s Law numerical example # 1 http://www.studyphysics.ca/30/coulomb.p df Coulomb’s Law numerical example # 2 http://www.physicsclassroom.com/Class/es tatics/U8L3b.cfm

34. Credits Electric field lines www.glenbrook.k12.il.us/.../estatics/ u8l4c.html www.glenbrook.k12.il.us/.../estatics/ u8l4c.html