HVAC - CH 12 - Basic Electricity and Magnetism

1. what are the three main components of atoms? a. electrons, positrons, and muons b. protons, neutrons, and electrons c. photons, neutrinos, and quarks d. ions, isotopes, and isomers

b. protons, neutrons, and electrons. atoms are made up of these three main components.

2. neutrons contribute significantly to the electrical characteristics of an atom. true or false?

false. neutrons have no charge and have little or no effect as far as electrical characteristics are concerned.

3. the number of electrons orbiting an atom's nucleus is always equal to the number of which other component within that atom? a. neutrons b. protons c. positrons d. nuclei

b. protons. the number of electrons in an atom is equal to the number of protons in the atom.

4. according to the formula 2s^2, how many electrons can the first shell of an atom hold? a. 1 b. 2 c. 4 d. 8

b. 2. for the first shell (s=1), 2 times 1 squared equals 2.

5. what term describes electrons in the outermost shell of an atom? a. core electrons b. binding electrons c. valence electrons d. orbital electrons

c. valence electrons. the term valence electrons refers to the electrons in the outermost, or valence, shell.

6. an atom becomes stable when its outermost shell is either completely full or completely empty. true or false?

true. being stable refers to having either a completely full or a completely empty outermost shell.

7. when an electron leaves an atom, the atom will have a net positive charge. true or false?

true. when electrons leave an atom, the atom will contain more protons than electrons, resulting in a net positive charge.

8. the law of charges states that opposite charges repel each other. true or false?

false. the law of charges states that like charges repel each other and unlike or opposite charges attract each other.

9. which of the following elements is known for having only one electron in its outer orbit, contributing to its excellent conductivity? a. aluminum b. mercury c. copper d. glass

c. copper. copper has only one electron in its outer shell, making it a good conductor.

10. according to the american wire gauge (awg), what is generally true about thicker wires or conductors? a. they have higher resistance. b. they can carry more current safely. c. they are poorer conductors of heat. d. they are only used for direct current.

b. they can carry more current safely. thicker wires or conductors can carry more current safely than thinner wires or conductors.

11. which of these materials is specifically listed as a good insulator? a. silver b. plastic c. aluminum d. mercury

b. plastic. glass, air, rubber, and plastic are examples of good insulators.

12. the electricity that air-conditioning and heating technicians are most involved with is produced by which method? a. chemicals b. light c. pressure d. magnetism

d. magnetism. the material states hvacr technicians are more involved with electricity produced by magnetism.

13. when a conductor such as a copper wire crosses the lines of force of a magnetic field, what happens to the outer electrons in the wire's atoms? a. they become tightly bound. b. they are freed and begin to move from atom to atom. c. they switch their charge from negative to positive. d. they vibrate in place without moving.

b. they are freed and begin to move from atom to atom. if a conductor crosses the lines of force, the outer electrons in the atoms in the wire are freed and begin to move.

14. the speed at which electrons travel through a wire in a battery-powered lamp is approximately 186,000 miles per second. true or false?

false. the energy of electromagnetic waves travels at that speed, but the electrons themselves flow at about 3 inches per hour.

15. in an electrical generator, which factor will produce more current? a. a smaller magnetic field b. fewer turns of wire passing through the field c. a large magnetic field with many turns of wire d. a constant, non-moving magnetic field

c. a large magnetic field with many turns of wire. a large magnetic field will produce more current than a smaller one, and many turns of wire will produce more than a few.

16. what is direct current (dc) considered to flow from? a. positive to negative b. negative to positive c. alternating positive and negative d. neutral to ground

b. negative to positive. dc is considered to flow from negative to positive.

17. alternating current (ac) is generally more economical to transmit electrical energy long distances than direct current (dc). true or false?

true. it is much more economical to transmit electrical energy long distances in the form of ac, as the transmission losses are very low compared to those associated with dc.

18. what is the unit used to measure electromotive force (emf)? a. ampere b. ohm c. volt d. watt

c. volt. electromotive force (emf), or voltage (v), is measured in volts.

19. one coulomb is defined as exactly 6.24 x 10^18 electrons. true or false?

true. one coulomb is defined as 6.24 x 10^18 electrons.

20. a resistance of 1 ohm is present when a force of how many volts causes a current of 1 ampere to flow? a. 0.1 v b. 1 v c. 10 v d. 100 v

b. 1 v. a resistance of 1 ohm is present when a force of 1 volt causes a current of 1 ampere to flow.

21. as the resistance of an electric circuit drops, what happens to the current flow through the circuit? a. it will drop b. it will increase c. it will remain constant d. it will oscillate

b. it will increase. as the resistance of a circuit drops, the current flow through the circuit will increase.

22. which of the following is not listed as a necessary component of a basic electric circuit? a. a power source b. a load c. a complete conductive path d. a capacitor

d. a capacitor. the required components are a power source, a load, a complete conductive path, and generally a means for starting and stopping current flow.

23. when measuring voltage with a digital multimeter (dmm), how is the dmm connected to the portion of the circuit being evaluated? a. in series b. in parallel c. in perpendicular d. directly to ground

b. in parallel. the dmm is connected in parallel with the portion of the circuit being evaluated.

24. what does the 'i' in ohm's law stand for? a. impedance b. inductance c. intensity of current d. insulation

c. intensity of current. the 'i' stands for intensity of current, or amperage.

25. if you know the amperage (i) and resistance (r) in a circuit, what formula can you use to find the voltage (e)? a. e = i / r b. e = r / i c. e = i x r d. e = i + r

c. e = i x r. the voltage equals the amperage times the resistance.

26. a heating element with a resistance of 40 ohms is connected to a 120 v supply. what current flows through it? a. 0.33 a b. 3 a c. 480 a d. 120 a

b. 3 a. using i = e / r, current = 120 v / 40 ohms = 3 a.

27. in a series circuit, how does the total current flow relate to the current flowing through each individual resistance? a. it is divided among them. b. it is the same through each resistance. c. it is inversely proportional. d. it doubles at each resistance.

b. it is the same through each resistance. the total current flows through each resistance or load in the circuit.

28. three resistances with values of 5 ohms, 10 ohms, and 15 ohms are wired in series. what is their total resistance? a. 1.875 ohms b. 15 ohms c. 30 ohms d. 50 ohms

c. 30 ohms. in a series circuit, r_total = r1 + r2 + r3, so 5 + 10 + 15 = 30 ohms.

29. to accurately measure the resistance of a circuit component with a dmm, the component must be disconnected from the circuit and the power must be off. true or false?

true. resistance should only be measured on circuits and components that are deenergized, and the component should be disconnected from the circuit.

30. in a parallel circuit, what is the relationship between the total voltage and the voltage supplied to each individual branch? a. the total voltage is divided among the branches. b. the total voltage is the same across each branch. c. the total voltage is the sum of the branch voltages. d. the total voltage is inversely proportional to branch voltage.

b. the total voltage is the same across each branch. the total voltage is applied across each circuit branch, meaning etotal = e1 = e2 = e3 = …

31. if a parallel circuit has multiple resistive paths added, what happens to the total resistance of the circuit? a. it increases. b. it decreases. c. it remains the same. d. it becomes infinite.

b. it decreases. as more and more resistive paths or branches are added to the parallel circuit, the total resistance of the circuit gets lower and lower.

32. electrical power (p) is determined by multiplying the voltage (e) and the circuit amperage (i) together. true or false?

true. watts = volts times amperes, or p = e times i.

33. what is the equivalent of 1 kilowatt (kw) in watts (w)? a. 10 w b. 100 w c. 1,000 w d. 10,000 w

c. 1,000 w. a kilowatt is equal to 1000 w.

34. a circuit consumes 2640 w of power. how many kilowatts (kw) is this? a. 0.264 kw b. 2.64 kw c. 26.4 kw d. 264 kw

b. 2.64 kw. to determine kilowatts, divide watts by 1000: 2640 w / 1000 = 2.64 kw.

35. which type of temporary magnet is extensively used in many electrical components of air-conditioning and refrigeration equipment? a. permanent magnets b. bar magnets c. electromagnets d. ceramic magnets

c. electromagnets. electromagnets, a type of temporary magnet, are used in many electrical components of hvacr equipment.

36. what happens to the strength of the magnetic field generated around a wire if the wire is formed into a loop and then wound into a coil? a. it decreases at each step. b. it remains constant. c. it increases with each step. d. it becomes unstable.

c. it increases with each step. if the wire is formed into a loop, the strength increases; if wound into a coil, it creates an even stronger magnetic field.

37. what is the name for a coil of wire carrying an electrical current that can attract or pull an iron bar into the coil? a. an inductor b. a capacitor c. a solenoid d. a transformer

c. a solenoid. this coil of wire carrying an electrical current is called a solenoid.

38. in an ac circuit, the continual building up and collapsing of a magnetic field around a conductor induces an emf or voltage that does what? a. reinforces the existing voltage. b. neutralizes the existing voltage. c. opposes the existing voltage. d. converts the voltage to direct current.

c. opposes the existing voltage. this process produces an emf, or voltage that opposes the existing voltage in the conductor.

39. what specific type of resistance is produced in an ac circuit by components like coils and transformers due to opposing induced voltage? a. pure resistance b. capacitive reactance c. inductive reactance d. ohmic resistance

c. inductive reactance. this opposition is called inductive reactance.

40. electric motors are classified as what type of loads because they contain coils of wire and primarily generate a magnetic field? a. resistive loads b. capacitive loads c. inductive loads d. power loads

c. inductive loads. electric motors have coils of wire and are, therefore, referred to as inductive loads.

41. how do transformers produce voltage in a second circuit? a. through direct connection to a battery. b. through chemical reactions. c. through electromagnetic induction. d. through physical friction.

c. through electromagnetic induction. transformers are electrical devices that produce voltage in a second circuit through electromagnetic induction.

42. a step-up transformer has more windings in its primary than in its secondary. true or false?

false. a step-up transformer has more windings in the secondary than in the primary.

43. if a transformer's primary winding has 1000 turns and its secondary has 2000 turns, and 120 v is applied to the primary, what is the approximate induced voltage in the secondary? a. 60 v b. 120 v c. 240 v d. 480 v

c. 240 v. for a step-up transformer, the voltage is proportional to the turns ratio: (2000/1000) * 120 v = 240 v.

44. what common control voltage is often produced by additional step-down transformers used with air-conditioning and heating equipment? a. 12 v b. 24 v c. 120 v d. 240 v

b. 24 v. additional step-down transformers may be used to produce the 24 v commonly used in thermostats and other control devices.

45. what is the primary function of a capacitor in an electric circuit? a. to convert ac to dc. b. to increase current flow. c. to store electrical energy for later use. d. to provide resistance to current.

c. to store electrical energy for later use. a capacitor is a device in an electric circuit that stores electrical energy for later use.

46. a simple capacitor is composed of two plates with what type of material between them? a. conductive b. resistive c. insulating d. magnetic

c. insulating. a simple capacitor is composed of two plates with insulating material between them, referred to as a dielectric.

47. the capacitance of a capacitor is determined by the distance between the plates, the surface area of the plates, and the dielectric material. true or false?

true. these three physical characteristics are listed as determining capacitance.

48. what is the symbol for the unit microfarad? a. mf b. μf c. uf d. nm

b. μf. the symbol for micro is μ and for farad is f, so μf.

49. what term describes the total opposition to current flow in an ac circuit, encompassing pure resistance, inductive reactance, and capacitive reactance? a. admittance b. susceptance c. impedance d. conductance

c. impedance. the total effect of these three is called impedance.

50. in an ac circuit that has only pure resistance, how are the voltage and current typically phased? a. voltage leads current. b. current leads voltage. c. voltage and current are in phase. d. they are 90 degrees out of phase.

c. voltage and current are in phase. in a pure resistive circuit, the voltage and current will be in phase with each other.

51. what instrument is used to measure voltage, current, resistance, and sometimes temperature, and is most often used by hvacr technicians? a. oscilloscope b. megohmmeter c. digital multimeter (dmm) d. clamp-on ammeter (solely)

c. digital multimeter (dmm). a digital multimeter, commonly referred to simply as a dmm, is this instrument.

52. when using a dmm to measure an unknown voltage, it is always best to start at the highest range setting. true or false?

true. if uncertain about the magnitude of the measurement, it is always best to start at the highest range.

53. when measuring resistance with a dmm, what reading indicates infinite resistance or an open line? a. 0 ohms b. ol c. hi d. lo

b. ol. on dmms, infinite resistance is often displayed as "ol," which stands for "open line" or "open lead."

54. what is the standard frequency of alternating current in the united states and canada? a. 50 hz b. 60 hz c. 120 hz d. 240 hz

b. 60 hz. the standard frequency in this country and canada is 60 hz.

55. the effective voltage measured by most electrical test instruments is known as what value? a. peak voltage b. peak-to-peak voltage c. root-mean-square (rms) voltage d. average voltage

c. root-mean-square (rms) voltage. the effective voltage is the rms voltage.

56. the resistance of a conductor depends on its material, its cross-sectional area, its temperature, and its length. true or false?

true. these four factors are listed as determining the resistance of a conductor.

57. what is the relationship between the american standard wire gauge (awg) number and the wire's diameter and resistance? a. increasing awg number indicates larger diameter and lower resistance. b. increasing awg number indicates smaller diameter and greater resistance. c. awg number indicates only the wire's length. d. awg number indicates only the wire's material.

b. increasing awg number indicates smaller diameter and greater resistance. for example, number 12 wire is smaller than number 10 wire.

58. what is the term for the current-carrying capacity of a conductor? a. wattage b. voltage drop c. ampacity d. impedance

c. ampacity. the conductors are sized by their amperage-carrying capacity, called ampacity.

59. the national electrical code (nec) includes a footnote exception for small conductors (no. 14 and no. 12 copper) in residential houses. what is the reason for this exception? a. to encourage the use of larger wires. b. to account for intentional overloading by professionals. c. because circuits are often unintentionally overloaded by homeowners. d. to simplify wire sizing calculations.

c. because circuits are often unintentionally overloaded by homeowners. the footnote exception simply adds more protection because number 12 and number 14 wire are used in residential houses where circuits are often overloaded unintentionally by the homeowner.

60. what type of device uses a metal strip with a higher resistance and a relatively low melting point to open a circuit when current exceeds its rating? a. circuit breaker b. ground fault circuit interrupter c. fuse d. relay

c. fuse. a fuse is a simple device containing a strip of metal that heats up faster than the conductor and melts to open the circuit.

61. after a fuse opens a circuit, it can be reset and reused. true or false?

false. fuses are one-time devices and must be replaced when the strip or element melts.

62. which type of fuse is frequently used in circuits with electric motors because it can handle the higher starting current? a. edison-base plug fuses b. ferrule cartridge fuses c. dual-element fuses d. knife-blade cartridge fuses

c. dual-element fuses. dual-element fuses are frequently used in this situation because they allow for the higher starting current of an electric motor.

63. what component in a circuit breaker causes it to trip and open the circuit when there is a short circuit or other excessive current overload over a short period of time? a. bimetal strip b. common-trip mechanism c. magnetic coil d. arc-quenching material

c. magnetic coil. the magnetic coil causes the breaker to trip and open the circuit when there is a short circuit or other excessive current overload over a short period of time.

64. what is the primary purpose of a ground fault circuit interrupter (gfci)? a. to prevent circuit overloads. b. to protect individuals against electric shock. c. to regulate circuit voltage. d. to extend equipment lifespan.

b. to protect individuals against electric shock. gfcis help protect individuals against shock in addition to providing current overload protection.

65. a gfci will interrupt current flow if it senses a current difference as small as 20 milliamperes. true or false?

true. current differences as small as 20 milliamps, or 0.02 a, will cause the gfci to interrupt current flow.

66. in their pure form, silicon and germanium are considered good conductors of electricity. true or false?

false. in their pure form, semiconductors, as their name implies, do not conduct electricity very well.

67. what process is used to add impurities to silicon or germanium to control their conductivity, thereby creating p-type or n-type materials? a. purification b. crystallization c. doping d. annealing

c. doping. this process is called doping.

68. when silicon is doped with boron, which has three valence electrons, what type of semiconductor material is created? a. n-type material b. p-type material c. intrinsic material d. metallic material

b. p-type material. since boron atoms each have three valence electrons, the addition of this impurity creates a hole, resulting in p-type material.

69. what simple solid-state devices consist of p- and n-type material connected together and allow current to flow in only one direction? a. transistors b. rectifiers c. thermistors d. diodes

d. diodes. diodes are simple solid-state devices consisting of p- and n-type material connected together.

70. for a diode to have forward bias (current flow), the negative terminal on the battery should be connected to which part of the diode? a. anode b. cathode c. gate d. base

b. cathode. the negative terminal on the battery should be connected to the cathode.

71. a diode can be used as a solid-state rectifier to change alternating current (ac) to direct current (dc). true or false?

true. a diode can be used as a solid-state rectifier, changing ac to dc.

72. what type of rectifier circuit takes the negative portion of the ac cycle and flips it to the positive side, allowing current to flow for the entire cycle? a. half-wave rectifier b. full-wave bridge rectifier c. uncontrolled rectifier d. single-phase rectifier

b. full-wave bridge rectifier. this is a common full-wave rectifier that allows current to flow for the entire cycle.

73. how many sections of semiconductor material are bonded together to form a silicon-controlled rectifier (scr)? a. two b. three c. four d. five

c. four. scrs consist of four sections of semiconductor material bonded together, forming a pnpn junction.

74. what is the control element in an scr? a. anode b. cathode c. gate d. emitter

c. gate. the gate is the control for the scr.

75. a transistor used as a switch or to amplify an electrical signal is made of how many pieces of semiconductor materials sandwiched together? a. two b. three c. four d. five

b. three. transistors are made of three pieces of semiconductor materials sandwiched together.

76. in an npn transistor, the emitter is connected to the negative polarity. true or false?

true. in the npn type, the collector and the base are connected to the positive; the emitter is connected to the negative.

77. what type of resistor is sensitive to temperature and changes its resistance with temperature fluctuations? a. potentiometer b. varistor c. thermistor d. photoresistor

c. thermistor. a thermistor is a type of resistor that is sensitive to temperature.

78. a positive temperature coefficient (ptc) thermistor causes its resistance to decrease when the temperature increases. true or false?

false. a ptc thermistor causes the resistance of the thermistor to increase when the temperature increases.

79. a diac is a two-directional electronic device whose output is what type of current? a. dc b. ac c. pulsating dc d. variable dc

b. ac. its output is ac, as it operates in both halves of the ac waveform.

80. what type of switching device will conduct on both halves of the ac waveform and is commonly used for motor speed control of ac motors? a. diode b. transistor c. diac d. triac

d. triac. a triac is a switching device that will conduct on both halves of the ac waveform and is commonly used for motor speed control.

81. what is the purpose of a heat sink in relation to solid-state devices? a. to increase the device's electrical conductivity. b. to provide structural support for the device. c. to dissipate excess heat generated by the device into the surrounding air. d. to amplify the device's signal output.

c. to dissipate excess heat generated by the device into the surrounding air. heat sinks dissipate heat that could change the operation of the device or destroy it.

82. to understand the theory of how electric current flows, one must understand something about matter and its components. true or false?

true. to understand the theory of how electric current flows, you must understand something about matter and what it is made of.

83. protons and neutrons are located at the center, or nucleus, of the atom. true or false?

true. protons and neutrons are located at the center (or nucleus) of the atom.

84. a hydrogen atom is simple to illustrate because it has how many protons and electrons? a. two protons and two electrons b. one proton and one electron c. zero protons and one electron d. one proton and two electrons

b. one proton and one electron. the hydrogen atom is simple to illustrate because it has only one proton and one electron.

85. copper is commonly used to construct electric circuits due to its specific atomic structure, featuring how many protons and electrons? a. 1 proton, 1 electron b. 8 protons, 8 electrons c. 29 protons, 29 electrons d. 32 protons, 32 electrons

c. 29 protons, 29 electrons. copper, which is commonly used, has 29 protons and 29 electrons.

86. what term describes an atom with a shortage of electrons and a net positive charge? a. negatively charged atom b. neutral atom c. positively charged atom d. ionized atom

c. positively charged atom. when electrons leave an atom, it will have a net positive charge.

87. an electron (negative charge) entering an orbit with a surplus of electrons will tend to do what to an electron already there? a. attract it b. bond with it c. repel it d. neutralize it

c. repel it. an electron entering an orbit with a surplus of electrons will tend to repel an electron already there.

88. what characteristic of metallic substances makes them good conductors of electricity? a. their tightly bound valence electrons. b. their eagerness to give up "loose" valence electrons. c. their high melting points. d. their ability to absorb electrons.

b. their eagerness to give up "loose" valence electrons. metallic substances facilitate current flow by not holding onto their valence electrons tightly and by allowing them to move freely from atom to atom.

89. besides glass, air, rubber, and plastic, what other category of substances generally makes better insulators? a. metallic substances b. non-metallic substances c. semiconductor substances d. magnetic substances

b. non-metallic substances. generally speaking, non-metallic substances make better insulators.

90. what are the usually designated poles of a magnet? a. positive and negative b. anode and cathode c. north and south d. primary and secondary

c. north and south. magnets have poles, usually designated as the north (n) pole and the south (s) pole.

91. the movement of electrons in one direction, causing current, is best described as what? a. a continuous stream of fast-moving electrons. b. an impulse transferred from one electron to the next. c. electrons physically traveling at the speed of light. d. a constant flow of protons.

b. an impulse transferred from one electron to the next. current is, in its simplest terms, an impulse transferred from one electron to the next.

92. what type of current travels in one direction and provides a constant voltage to the circuit being powered? a. alternating current b. direct current c. pulsating current d. inductive current

b. direct current. direct current (dc) is so-named because it travels in one direction and provides a constant voltage.

93. solid-state or electronic circuits referred to as rectifiers can create direct current (dc) from alternating current (ac) power sources. true or false?

true. direct current can also be created from alternating current (ac) power sources by utilizing solid-state or electronic circuits referred to as rectifiers.

94. what is the unit for amperage, representing the electron flow rate? a. volt b. ohm c. ampere d. watt

c. ampere. the ampere is the unit used to measure the quantity of electrons moving past a given point in a specific period of time (electron flow rate).

95. the abbreviation for ampere is 'a'. true or false?

true. the abbreviation for ampere is a.

96. what type of ladder should be used to insulate oneself from wet floors and help prevent electric shock? a. aluminum b. steel c. conducting d. rubber-soled work boots (this is about footwear, not ladder)

d. rubber-soled work boots (this is about footwear, not ladder). the safety tip says "use non-conducting ladders, such as fiberglass or wood" to avoid becoming part of an electric circuit.

97. what does the symbol 'v' represent in electrical measurements? a. ampere b. ohm c. volt d. watt

c. volt. volt represents electrical force or pressure (v).

98. a simple electric circuit must have a power source, a load, and a complete conductive path. true or false?

true. an electric circuit must have a power source, a load or device to consume the power, as well as a complete conductive path to and from the power source.

99. which of the following diagrams uses symbols to represent an electrical generator, a light bulb, and a switch? a. figure 12.11 b. figure 12.12 c. figure 12.13 d. figure 12.14

c. figure 12.13. figure 12.13 illustrates the same circuit, without the dmm and clamp-on ammeter, using symbols.

100. what is the internal resistance of ammeters intended for connection in series with circuit loads? a. very high b. very low c. moderate d. negligible

b. very low. the internal resistance of ammeters intended for connection in series with circuit loads is very low.