When combing your hair you scuff electrons

Physics 1010-010 Syllabus Page 1

Assignments

Conceptual Physics Twelth Edition Questions for Chapters 22 through 25 are due October29.

Chapter 22

Questions: 3, 4, 5, 20, 36, 53, 54, 62, 92, 106

3. Which part of an atom is positively charged, and which part is negatively charged?

4. How does the charge of one electron compare with the charge of another electron? How does it compare with the charge of a proton?

5. What is most commonly the net charge of an atom?

20. What is the primary purpose of a lightning rod?

36. Two point charges are separated by 6 cm. The attractive force between them is 20N. Find the force between them when they are separated by 12 c. (Why can you solve this problem without knowing the magnitudes of the charges?)

53. When combing your hair, you scuff electrons from your hair onto the comb. Is your hair then positively or negatively charged? How about the comb?

54. At some automobile toll booths, a thin metal wire protrudes from the road, making contact with the cars before they reach the tool collector. What is the purpose of this wire?

62. What does the invers-square law tell you about the relationship between force and distance?

92. Why is it safe to remain inside a car during a lightning storm?

106. If you are caught outdoors in a thunderstorm, why shouldn’t you stand under a tree? Can you think of a reason why you should not stand with your legs far apart? Or why lying down can be dangerous? (Hint: Consider the electric potential difference.)

Chapter 23

Questions: 9, 15, 16, 20, 22, 25, 29, 33, 51, 68, 82

9. Does heating a metal wire increase or decrease its electrical resistance?

15. Does a battery produce ac or dc? Does a generator at a power station produce ac or dc?

16. What does it mean to say that a certain current is 60 Hz?

20. Why does a wire that carries a current become hot?

22. A tripped domino sends a pulse along a row of standing dominoes. Is this a good analogy for the way electric current, sound, or both travel?

25. From where do the electrons originate that produce an electric shock when you touch a charged conductor?

29. In a circuit of two lamps in series, if the current through one lamp is 1 A, what is the current through the other lamb? Defend your answer.

33. What is the function of fuses or circuit breakers in a circuit?

51. In periods of peak demand, power companies lower their voltage. This save them power (and saves you money!). To see the effect, consider a 1200 W coffeemaker that draws 10 A when connected to 120V. Suppose the voltage is lowered by 10% to 108V. By how much does the current decrease? By how much does the power decrease? (Caution: The 1200-W label is valid only wen 120 V is applied. When the voltage is lowered, the current is lowered, so the power output of the toaster’s heating coils drops, which cools the coil and lowers it resistance. However, for this problem assume the change in resistance is slight.)

68. In which of the circuits shown does a current exist to the light bulb?

82. Would you expect to find dc or as in the filament of a light bulb in your home? In the headlight of an automobile?

Chapter 24

Questions: 6, 9, 10, 11, 19, 20, 47, 59, 62, 70

6. How does magnetic field strength relate to the closeness of magnetic field lines about a bar magnetic?

9. What is a magnetic domain?

11. Why is iron magnetic and wood is not?

19. In what direction relative to a magnetic field does a charged particle move in order to experience maximum deflection force? Minimum deflecting force?

20. What effect does Earth’s magnetic field have on the intensity of cosmic ray striking Earth’s surface?

47. By what mechanism do the iron filings shown about the magnet in Figure 24.2 align with the magnetic field?

59. Can an electron at rest in a stationary magnetic field be set into motion by a magnetic field? What about the electron placed at rest in an electric field?

62. A magnetic field can deflect a beam of electrons, but it cannot do work on the electrons to change their speed. Why?

70. Historically, replacing dirt roads with paved roads reduced friction of vehicles. Replacing pave roads with steel rails reduced friction further. What recent step eliminated rail friction of vehicles? What friction remains after rail friction is eliminated?

Chapter 25

Questions: 3, 6, 16, 18, 19, 21, 22, 24, 38

3. State Faraday’s law.

6. What are the basic differences and similarities between a generator and an electric motor?

16. Is it correct to say that a transformer boosts electric energy? Defend your answer.

16. No, a transformer boosts voltage, or reduces it, but not energy. That’s a conservation of energy no-no!

18. How does the power input to an efficient transformer compare with the power output?

19. What exactly does a step-down transformer step down?

21. Why does a transformer require ac?

22. What is the principal advantage of ac over dc?

24. What is the purpose of transmitting power at high voltages over long distances?

38. A model electric train requires 6 V to operate. When it is connected to a 120 V household circuit, a transformer s needed. If the primary coil of the transformer has 360 turns, show that the secondary coil should have 18 turns.