2. A body that is positively charged is one that has an excess number of electrons.

Transcription

1 TRUE/FALSE 1. An atom that has lost an electron is called a positive ion. Page: 1 2. A body that is positively charged is one that has an excess number of electrons. 3. An ampere is defined as the amount of current that flows through a circuit when coulombs of charge pass a given point in one second. 4. A volt is defined as the voltage that requires 1 joule of energy to move one coulomb of charge from one point to another. 5. Current in a dc circuit alternately flows in one direction then in the other. FILL-IN-THE-BLANK 6. Materials that have large numbers of free electrons that are able to move easily are called. 7. Materials that do not conduct electrons are called. 8. When a body is negatively charged, it is said to have a/an of electrons. 9. The charge on a single electron is. 10. The SI unit of measurement for force is the. MULTIPLE CHOICE 11. An atom that has gained an electron is called a. a. negative ion b. positive ion c. neutral ion d. semiconductor 12. Which one of the following materials is the best conductor of electrons? a. gold b. copper c. aluminum d. silicon 13. Which one of the following materials best represents a material used in the manufacture of semiconductors? a. carbon b. plastic c. rubber d. silicon

2 14. The SI unit of electrical charge is the. Page: The SI unit of electrical potential difference is the 16. The SI unit of electrical energy is the. 17. The SI unit of electrical current is the. 18. A battery that can be recharged is called a battery, while one that cannot be recharged is called a battery. a. cell, dc b. ac, cell c. primary, secondary d. secondary, primary 19. Which one of the following choices is not a type of cell or battery? a. lithium b. carbon-zinc c. aluminum carbide d. nickel cadmium 20. A dc generator converts energy to energy. a. mechanical, electrical b. electrical, mechanical c. dc, ac d. ac, dc SHORT ANSWER 21. Material X has 2 valence electrons and Material Y has 3. Which is the better conductor? 22. Material X has 6 valence electrons and Material Y has 8. Which is the better insulator?

3 Page: According to Coulomb's law, what is the amount and direction of change of force between two electrically charged bodies when the distance between them is reduced by one-half? 24. A coulomb is defined as the charge carried by a certain number of electrons. What is that number? 25. How much electrical charge does a single electron have? 26. A body initially has a 20 µc of negative charge. How many electrons must be removed in order to neutralize the charge? 27. There is found to be a force of 0.27 N between two electrically charged bodies that are separated by m. The charge on one body is C. What is the charge on the second body? 28. A certain circuit requires 12 joules of energy to move 1 coulomb of charge. What is the voltage level? 29. How much work is done when 300 µc of charge is moved across a 1.5 V potential? 30. If the voltage between two points is 24 µv, how much energy is required to move 3.12 million electrons? 31. Over a period of 20 µs, 600 µc of charge pass through a wire. What is the current level? 32. The average current drain from the battery in a hobby robot is 2.5 A. If you want the robot to operate at least 3 hours without recharging, what is the minimum life rating of the battery? 33. What happens to the service rating of a battery as the temperature increases? 34. A certain battery has a life rating of 1.2 Ah. In theory, how long (in seconds) can it deliver 100 A? 35. What kind of cell uses light to generate dc voltage?

4 Page: Figure 2-1 shows two different meter connections. Which connection, a or b, represents the proper connection for measuring voltage? 37. Figure 2-1 shows two different meter connections. Which connection, a or b, represents the proper connection for measuring current? 38. What is another name for a multimeter? 39. Which type of multimeter uses a needle to indicate measured values instead of a direct numerical readout? 40. What type of switch is shown in Figure 2-2? 41. What type of switch is shown in Figure 2-3? 42. Define each term and units of measurement for the following equation: F = k Q 1 Q 2 r 2

5 Page: Explain how an ampere can be properly defined as electrons passing a given point in one second. 44. Explain how the equation W = QV can be used to show that 1 joule is the amount of energy required to move electrons across a one-volt difference in potential. 45. Describe the difference in operation between a normally open (NO) pushbutton switch and a normally closed (NC) pushbutton switch. 46. Describe the purpose of a power supply.

6 1. True 2. False 3. False 4. True 5. False 6. conductors 7. insulators 8. excess C 10. newton (N) 11. a 12. a 13. d 14. a 15. d 16. c 17. b 18. d 19. c 20. a 21. Material X 22. Material Y 23. Increase 4 times C Answer Key Page: electrons C volts µj J A Ah 33. increases s 35. solar cell 36. b 37. a 38. Volt-Ohm-Milliammeter, or VOM 39. analog multimeter 40. single pole, double throw (SPDT) 41. normally open pushbutton 42. F = the force between two charged bodies in newtons k = a constant without units Q 1 and Q 2 = the charge on bodies 1 and 2 in coulombs r = the distance between the two bodies in meters

7 Answer Key Page: The textbook defines an ampere as 1 coulomb of charge passing a point in one second. The textbook also states that 1 coulomb is equal to electrons. By substituting the second statement into the first: an ampere is electrons passing a point in one second. 44. In the equation W = QV, the term Q is usually expressed as 1 coulomb. However, 1 coulomb of electrical charge is equal to the charge of electrons. It follows that electrons can be substituted for the term Q. 45. A normally open switch closes when it is depressed. A normally closed switch opens when it is depressed. 46. A power supply converts incoming ac to the dc voltages required to operate electronic equipment.