1. Electrostatics
Physics I
By Scott Adams

2. Vocabulary
Electric Field
Electrostatics
Charge
Electron
Proton
Conductor
Insulator
Induction
Conduction
Electroscope
Coulomb’ Law

3. Video #1 Like charges attract each other
True b. False
What are/is a good example of conductors?
Copper b. Wood c. Gold d. A & C
How do you get a negatively charged object?
Gain electrons c. Lose electrons
Neither d. a & b
A negatively charged rod touches a neutral spherical conductor and then removed. The neutral object is now
Negative b. positive c. still neutral

4. − + + − + − Forces are equal and opposite!!! Charge Like Charges Repel
Unlike Charges Attract − +

5. Conservation of Charge:
During any process, the net electric charge of an isolated system remains constant
Conductors – allow electrons to flow easily – ex. Copper, Aluminum, Silver, Gold
Insulators – resist the flow of electrons – ex. Rubber, plastic, wood, air

6. Recall from Chemistry: a)How does an object become negatively charged?
Charging an object
When a rubber rod is rubbed with fur or wool, it becomes negatively charged.
(Cutnell & Johnson, 2004)
Recall from Chemistry:
a)How does an object become negatively charged?
b)Positively charged?
Gains Electrons
Loses Electrons

7. Celluloid
Sulfur
Rubber
Copper, Brass
Amber
Wood
Cotton
Human Skin
Silk
Cat Fur
Wool
Glass
Rabbit Fur
Objects at the top of the list have a greater affinity for electrons than objects at the bottom of the list.

8. (Phet, 2010)

9. The Electroscope
Knob
Leaves
(Stw, 2005)

10. Determine the Charge on the rod based on the activity of the leaves and electrons.
Pos.
Neg.
Leaves Spread more
Leaves Collapse
(Stw, 2005)

11. Charging by Conduction
(Cutnell & Johnson, 2004)

12. The Quantity of Charge
The quantity of charge (q) can be defined in terms of the number of electrons, but the Coulomb (C) is a better unit for later work. A temporary definition might be as given below:
The Coulomb: 1 C = 6.25 x 1018 electrons
Which means that the charge on a single electron is:
1 electron: e- = -1.6 x C
Slide Author: (Tippens, 200a7)

13. Units of Charge
The coulomb (selected for use with electric currents) is actually a very large unit for static electricity. Thus, we often encounter a need to use the metric prefixes.
1 mC = 1 x 10-6 C
1 nC = 1 x 10-9 C
Slide Author: (Tippens, 2007a)

14. Charge
Sphere A carries a charge of +3 C and an identical sphere B is -1C. If the spheres touch one another and then are separated, the charge on sphere B would be
+3C
-1C
+3C
-1C
+3+-1 = +2C
+1C

15. Another Example of Charge
Sphere A carries a charge of -6C and an identical sphere B is -10C. If the spheres touch one another and then are separated, the charge on spheres A and B would be
-6C
-10C
-6C
-10 C ? ?

17. Video #2
During induction, the neutral charge gains what type of charge
a. same b. opposite
2. The electric fields get stronger as you travel outward
a. True b. False
3. A positive test charge of 3x10-5C is placed in an electric field. The force on it is 0.50N. What is the magnitude of the Electric field?
a. 1.5x105 b. 6 c. 6,000 d. 17,000
4. When you have two equal but opposite charges the electric field lines _______________?
a. leave the – charge and enter the + charge
b. leave the + charge and enter the – charge
c. Travel away from each other
d. nothing

18. Pith Ball Demo (No Sound)

19. Charging by Induction

20. Charging by Induction

21. The Electrophorus 1. 2. 3. 4.
How does the pith ball behave after being touched with the plate?

22. Electrophorus – You Tube

23. Electrophorus

24. Magnitude of Electric Fields
E = Electric Field Intensity (N/C)
Electric Fields Sample Problem
1. A positive test charge of 4 x 10-5 C is placed in an electric field. The force on it is 0.60 N. What is the magnitude of the electric field at the location of the test charge?

25. Field lines go away from positive charges and toward negative charges.
Electric Field Lines
Electric Field Lines are imaginary lines drawn in such a way that their direction at any point is the same as the direction of the field at that point. + Q - -Q
Field lines go away from positive charges and toward negative charges.
Slide Author: (Tippens, 2007b)

26. Examples of E-Field Lines
Two equal but opposite charges.
Two identical charges (both +).
Notice that lines leave + charges and enter - charges.
Also, E is strongest where field lines are most dense.
Slide Author: (Tippens, 2007b)
Various Electric Field Configurations

27. The E-Field at a distance d from a single charge Q
Inverse –Square Relationship
E = Electric Field Intensity (N/C)
E Field Strength
Decreases

28. The E-Field at a distance d from a single charge Q
F is the force on the test charge, qo.
+qo +Q d
-qo F

29. Draw Electric Fields at C in the square below:
-q q
In which region(s) could the electric field be zero?
I II III C r
+q q
+q q

30. Electric Fields inside a Hollow Conductor
E = 0 inside the conductor
(Cutnell & Johnson, 2004)

31. Electric Fields and Conductors Summary
    The electric field inside a conductor is zero when the charges are at rest.
Electric fields do not cross each other
Electric fields do not loop together
  Any net charge on a good conductor is distributed equally
on the surface.
(Cutnell & Johnson, 2004)

32. Electric Fields and Conductors Summary
  The electric field is always perpendicular
to the surface of a conductor.
  Inside a nonconductor, an electric field can exist.
   On an irregularly shaped conductor, charge tends to accumulate where the radius of curvature of the surface is smallest, that is at sharp points. + - ++
+ + +

33. Van De Graaph Generator – Mythbusters – YouTube
(Dake, 2006)
Van De Graaph Generator – Mythbusters – YouTube

34. Faraday’s Cage at Boston Museum
E = 0 inside conductor
(Tyrtle, 2008)

36. Video #3 What is the value for K? 1.6x10-19 Nm2/C2 b. -1.6x10-19 Nm/C
c x109 Nm2/C d. -9x109 Nm/C
Two charges double the distance between them, the new force will be what __________ the original force?
4 b. ½ c. 2 d. ¼
Two charged spheres both with the charge of 4x10-5 C are held a distance of 2 meters apart. What is the magnitude of the force?
a. 3.6 b. 1x10-5 c. 2x10-5 d. 14.4
A positive charge moves to the right through a magnetic field pointing up. What direction is the force on the charge?
a. Down b. out of page c. into page c. left

37. q(charge) = Coulombs (C) Coulomb’s Law:
Like charges experience forces away from each other while unlike charges experience forces towards each other
k = 9x109 Nm2/C2
q(charge) = Coulombs (C)
Coulomb’s Law:
                         
                          
           F
Inverse square relationship r
(Cutnell & Johnson, 2004)
-e = x C , mass of electron = 9.11x10-31 kg

39. Coulomb’s Law - Sample Problems
1. Find the magnitude of the force between the two charges.
2 m
 
+5C -3C
Solution:
q1= +5C = 5x10-6 C
q2 = -3C = -3x10-6 C
k = 9x109 Nm2/C2
r = 2m
F = ?
Formula:
Substitute:

40. 2. Find the resultant force on each charged particle.
5 cm
 
+6C C

41. 3. A force of 1 N exists between the two charges below
3. A force of 1 N exists between the two charges below. How far apart are the charges? ?
 
+5C C

43. Faraday Cage Video – Teacher Tube
University of Tehran High Voltage Lab. Person in cage: Prof. H.Mohseni

44. Fun with a Giant Tesla Coil - Video

45. Faraday Cage & Cars – You Tube

46. References:
Adams. S. (1999). Dilbert Cartoon. Received from 2007 AP Conference complimentary resource CD. ( )
Cutnell & Johnson Physics. (2004). [Text Art CD]. John Wiley & Sons.
Nave, R. (2010). Hyperphysics.[Illustration]. Permission granted to use illustrations. Retrieved from
Phet (2010). Balloons and static electricity. Interactive Simulations. University of Colorado. Retrieved from
Ross Shepard Physics (n.d.) Electroscope Applet [video of Animation]. Retrieved from
Sal44sal44. (2006). Faraday Cage. [Video]. Retrieved from
Studyvilla.com (n.d.) Equipotential surfaces. Electrostatics II. [Illustration]. Retrieved on December 22, 2010 from
Tippens, P. (2007a). Chapter 23 Electric Force. [PowerPoint Slides]. Received from 2007 AP Conference Complimentary Resource CD
Tippens, P. (2007b). Chapter 26 Electric Field. [PowerPoint Slides]. Received from 2007 AP Conference Complimentary Resource CD.

47. Tippens, P. (2007d). Electric Potential. [PowerPoint Slides]
Tippens, P. (2007d). Electric Potential. [PowerPoint Slides]. Received from 2007 AP Conference Complimentary Resource CD.
Tyrtle, T. (2008). Van de Graaf Generator – Boston Museum of Science. Retrieved on December 22, 2010 from