Welcome to Physics 112

# Welcome to Physics 112

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## Welcome to Physics 112

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##### Presentation Transcript

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. Grounding 127

29. Insulators and Conductors • Polarization of charge

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

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

32. 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).

33. 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).

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

35. 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

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

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

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

39. 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 …?

40. 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.

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

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

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

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