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Class 2

Class 2. Today we will: learn the basic characteristics of the electrostatic force review the properties of conductors and insulators learn what is meant by “electrostatic induction” find out why static electrostatic forces are usually attractive

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Class 2

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  1. Class 2 • Today we will: • learn the basic characteristics of the electrostatic force • review the properties of conductors and insulators • learn what is meant by “electrostatic induction” • find out why static electrostatic forces are usually attractive • discuss the problem of force at a distance • learn the basics of two types of models that explain • why there are forces

  2. Clicker Question 1 When babies are rubbed, they gain a net charge. Does the ceiling need a net charge for the babies to stick to it? A. yes B. no

  3. Clicker Question 2 If the ceiling has no net charge, is it possible for the babies to be repelled by the ceiling? A. yes B. no

  4. Clicker Question 3 If the virtual particles were uncharged real particles, the force would be A. always attractive. B. always repulsive. C. either attractive or repulsive. D. There would be no force.

  5. Answers 1B 2B 3B

  6. Class 3 • Today we will: • learn how the thread model describes the force between • point charges at rest • construct Coulomb’s law from the thread model • learn how to use Coulomb’s law to calculate the force • between charges at rest

  7. Clicker Question 1 source charge field charge Force The field particle is A. positive B. negative C. neutral D. You can’t tell.

  8. Clicker Question 2 +3C (2, 3) −4C (7, 1) If we wish to find the force on the blue particle, A. the blue particle is the source particle. B. the blue particle is the field particle. C. both particles are source particles. D. both particles are field particles. E. none of the above.

  9. Clicker Question 3 +3C (2, 3) −4C (7, 1) The vector goes from the source particle to the field particle.

  10. Answers 1A 2B 3D

  11. Class 4 • Today we will: • review the meaning of potential energy • find the potential energy of point charges at rest • learn a few basic ideas about relativity • find out how relativity affects the threads emitted • by a moving source

  12. Clicker Question 1 In a region of space, the force on a positive test charge is zero. In this region, the potential energy is A. positive. B. negative. C. zero. D. a constant, but not necessarily zero.

  13. Clicker Question 2 The SI units for β are: A. m/s2 B. m2/s C. m2/s2 D. βis dimensionless

  14. H' H  L' L Clicker Question 3 rest moving

  15. Answers 1D 2D 3E

  16. Class 5 • Today we will: • learn the meaning of head lines, tail lines, and • ray lines. • find a force equation for a moving source • charge (like Coulomb’s law, but for a source with • constant velocity). • learn how stubs can be used to make a • account for the motion of field particles.

  17. Clicker Question 1 P B D E - out of screen A C U S A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the thread?

  18. Clicker Question 2 P B D E - out of screen A C U S A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the thread (electric) force?

  19. Clicker Question 3 P B D E - out of screen A C U S A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the head line?

  20. Clicker Question 4 P B D E - out of screen A C U S A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the stub?

  21. Clicker Question 5 B P A E - out of screen C D U S A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the stub (magnetic) force?

  22. Answers 1B 2B 3D 4E 5D

  23. Class 6 • Today we will: • learn that threads and stubs can be aligned to form electric and magnetic field lines. • derive the Lorentz force law. • integrate to find the electric and magnetic fields of a proton beam.

  24. Clicker Question 1 P B D E - out of screen A C U S A source charge and a field charge are both positive. The source at S emits threads that arrive at P when the source has moved to U. What is the direction of the stubs?

  25. Clicker Question 2 A proton travels vertically downward through a region where there is an electric field pointing to the east. What is the direction of the force? A. downward B. to the east C. to the south D. to the north E. to the west

  26. Clicker Question 3 A proton travels vertically downward through a region where there is a magnetic field pointing to the east. What is the direction of the force? A. downward B. to the east C. to the south D. to the north E. to the west

  27. Clicker Question 4 An electron travels vertically downward through a region where there is a magnetic field pointing to the east. What is the direction of the force? A. downward B. to the east C. to the south D. to the north E. to the west

  28. Answers 1E 2B 3C 4D

  29. Class 7 • Today we will: • learn how to do problems using the Lorentz force law. • learn the meaning of the electric potential and how it relates to the potential energy. • learn three ways of representing fields geometrically.

  30. Clicker Question 1 Before: • If we change the magnetic field to • what happens to the force? • It doubles. • Its get smaller by a factor of 2. • Its z-component doubles. • Its z-component gets smaller by factor of 2. • Nothing changes.

  31. Clicker Question 2 An electron passes through a 1.0 V battery. The electron charge is By how much does the energy of the electron increase?

  32. Clicker Question 2 An electron passes through a 1.0 V battery. The electron charge is Batteries increase the potential energy of electrons by pushing them closer together.

  33. Clicker Question 3 Two identical spheres have charges +q. They are separated by a distance d. At the midpoint between the spheres, the magnitude of the electric field is: +q +q

  34. Clicker Question 4 Two identical spheres have charges +q. They are separated by a distance d. At the midpoint between the spheres, the electric potential is: +q +q

  35. Answers 1E 2A 3E 4A

  36. Class 8 • Today we will: • learn about static electric fields and electric potentials in conductors. • learn how charges move in regions where there are electric and magnetic fields. • learn about some practical devices that use electric and magnetic fields.

  37. Clicker Question 1 • A net charge of +1.0 mC is placed on a steel ball. • The ball is then placed in the electric field of a • Van de Graaff generator. The total charge on the • surface of the steel ball is: • zero • + 0.5 mC • – 0.5 mC • + 1.0 mC • E. – 1.0 mC

  38. Clicker Question 2 • After a positive charge is “shot” into a region where • there is a uniform magnetic field, it spirals clockwise • out of the screen. If a negative charge were shot • into this region, it would: • spiral clockwise out of the screen • B. spiral clockwise into the screen • C. spiral counterclockwise out of the screen • D. spiral counterclockwise into the screen

  39. Answers 1D 2C

  40. Class 9 • Today we will: • learn about current, voltage, and power in circuits. • learn about resistance of materials and how resistance depends on geometry and temperature. • introduce Ohm’s law.

  41. Clicker Question 1 • What current passes through a 60 W light bulb? • (Line voltage is 120 V.) • 0.5 A • 1.0 A • 2.0 A • 7200 A • All of the above

  42. Clicker Question 2 One block has resistance R. What is the resistance when two blocks are joined at the midpoints as shown: • R/2 • R • 3R/2 • 5R/4 • 2R

  43. Clicker Question 2 One block has resistance R. What is the resistance when two blocks are joined at the midpoints as shown: • R/2 • R • 3R/2 • 5R/4 • 2R Hint: Divide the combination into three regions.

  44. Answers 1A 2D

  45. Class 10 • Today we will: • learn how to determine if two resistors are in series or parallel. • find out how resistors combine when connected in series and parallel. • work examples of series-parallel reduction to find current, voltage and power in resistance networks.

  46. Clicker Questions 1-6Series-Parallel QuizAnswer the following six questions to see if you understand what series and parallel mean.

  47. 1. Resistors A and B are in • series • parallel • neither

  48. 2. Resistors A and B are in • series • parallel • neither

  49. 3. Resistors A and B are in • series • parallel • neither

  50. 4. Resistors A and B are in • series • parallel • neither

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