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Welcome to Physics 112

Welcome to Physics 112. Instructor: Mike Talbot Web Page : delta.edu/mttalbot/physics112. Chapter 15. Electric Forces and Electric Fields. Introduction. Greek contributions (700 BC) Friction generates electricity Rub a piece of amber with wool. 61. Introduction.

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Welcome to Physics 112

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  1. Welcome to Physics 112 • Instructor: Mike Talbot • Web Page : delta.edu/mttalbot/physics112

  2. Chapter 15 Electric Forces and Electric Fields

  3. Introduction • Greek contributions (700 BC) • Friction generates electricity • Rub a piece of amber with wool 61

  4. Introduction • Charged particles • What are they? • What colors are they?

  5. Introduction • Coulomb’s Law • What does it say?

  6. Introduction • Electric fields • What is a gravitational field? • What is an electric field?

  7. Properties of Electric Charges • An electroscope may be used to demonstrate the existence of electrostatic forces. • It detects and identifies charges produced by such things as: • Plastic combs • Glass and silk • Hard rubber and wool • Balloons 62, 15.1

  8. Properties of Electric Charges • Walking across a carpet in the winter can also generate static electricity.

  9. Properties of Electric Charges • Dust accumulates on a TV screen because of the large static charge on the glass.

  10. Properties of Electric Charges • What should you do if a power line falls on your car while you are in it?

  11. Properties of Electric Charges • How many kinds of charge exist?

  12. Properties of Electric Charges • How many kinds of charge exist? • Two

  13. Properties of Electric Charges • Two kinds of charge (+ and -) • Named by Benjamin Franklin

  14. Properties of Electric Charges • Law of Charges 155

  15. Properties of Electric Charges • Law of Charges • At least two particles are involved • Like charges repel, opposites attract. • Motion may result

  16. Properties of Electric Charges • Law of Charges • At least two particles are involved • Like charges repel, opposites attract. • Motion may result • Planetary model of the atom 125

  17. Properties of Electric Charges • Are atoms neutral?

  18. Properties of Electric Charges • What is meant by the conservation of charge?

  19. Properties of Electric Charges • What is meant by the quantization of charge (e)

  20. Properties of Electric Charges • Demonstrating the quantization of charge (e) • The Millikan Oil-Drop Experiment • Measured the elementary charge on an electron 15.21

  21. Insulators and Conductors • Materials may be classified by their ability to conduct electricity.

  22. Insulators and Conductors • Materials may be classified by their ability to conduct electricity. • Conductors (many free electrons) • Insulators (few free electrons)

  23. Insulators and Conductors • Materials may be classified by their ability to conduct electricity. • Conductors (many free electrons) • Insulators (few free electrons) • Semiconductors

  24. Insulators and Conductors • What are some examples of good conductors?

  25. Insulators and Conductors • What are some examples of good insulators?

  26. Insulators and Conductors • What is an example of asemiconductor? • Where are semiconductors used? 225

  27. Charging by Friction

  28. Charging by conduction 15.3

  29. Charging by induction 15.4

  30. Grounding 127

  31. Insulators and Conductors • Polarization of charge

  32. Coulomb’s Law • An electric force has three properties: 15.6

  33. Coulomb’s Law • An electric force has three properties: • It is attractive or repulsive depending upon the sign of the charges.

  34. Coulomb’s Law • An electric force has three properties: • It is attractive or repulsive depending upon the sign of the charges. • It is directly proportional to the product of the magnitudes of the charges (q1.q2).

  35. Coulomb’s Law • An electric force has three properties: • It is attractive or repulsive depending upon the sign of the charges. • It is directly proportional to the product of the magnitudes of the charges (q1.q2). • It is inversely proportional to the square of the separation (r2).

  36. Coulomb’s Law • Coulomb’s formula:

  37. Coulomb’s Law • Definitions • Coulomb • The amount of charge that has passed a given point in one second when one ampere of current is flowing

  38. Coulomb’s Law • Definitions • Ampere • One coulomb of charge passing a given point in one second • Analogy: Like water flowing through a pipe

  39. Coulomb’s Law • Coulomb’s constant: ke = 8.9875 x 10 9 N.m2/C2

  40. Coulomb’s Law • Charges and masses of particles • Table 15.1 (pg. 501)

  41. Coulomb’s Law • Reminders: • Force is a vector quantity • r is the distance between centers • Newton’s Third Law applies • The Coulomb force is a field force just like …?

  42. Coulomb’s Law • Reminders: • Force is a vector quantity. • r is the distance between centers. • Newton’s Third Law applies. • The Coulomb force is a field force just likegravity.

  43. Coulomb’s Law • The two field force formulas are mathematically identical.

  44. Coulomb’s Law • The two field force formulas are mathematically identical. F = k q1q2/r2

  45. Coulomb’s Law • The two field force formulas are mathematically identical. F = k q1q2/r2 F = G m1m2/r2

  46. Coulomb’s Law • Differences between electrical and gravitational forces • Gravity only attracts

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