1. 1 Ω

2. 10 Ω

3. 100 Ω

4. 1 ΚΩ

5. 10 ΚΩ

6. 9 Ω

7. 90 Ω

8. 900 Ω

9. 9 kΩ

10. 90 kΩ

11. 32 Ω

12. 320 Ω

13. 3200 Ω

14. 32 kΩ

15. 320 kΩ

16. 56 kΩ

17. 560 Ω

18. 5600 Ω

19. 56 kΩ

20. 560 kΩ

21. 80 Ω

22. 800 Ω

23. 8000 Ω

24. 80 kΩ

26. 2.4 V

27. 9.6 V

28. 48 V

29. 240 V

30. 480 V

31. 960 V

32. 1.85 V

33. 7.4 V

34. 37 V

35. 185 V

36. 370 V

37. 740 V

38. 1.1 V

39. 4.4 V

40. 24 V

41. 110 V

42. 240 V

43. 440 V

44. 0.755 V

45. 3.1 V

46. 15.5 V

47. 75.5 V

48. 155 V

49. 310 V

50. 0.6 V

51. 2.4 V

52. 12 V

53. 60 V

54. 120 V

55. 240 V

56. 9.6 A

57. 2.4 A

58. 480 mA

59. 96 mA

60. 48 mA

61. 9.6 mA

62. 2.4 mA

63. 240 μA

64. 7.4 A

65. 2.4 A

66. 370 mA

67. 74 mA

68. 37 mA

69. 7.4 mA

70. 1.85 mA

71. 185 μA

72. 4.4 A

73. 1.1 A

74. 210 mA

75. 44 mA

76. 22 mA

77. 4.4 mA

78. 1.1 mA

79. 110 μA

80. 3.1 A

81. 0.755 A

82. 155 mA

83. 31 mA

84. 15.5 mA

85. 3.1 mA

86. 0.755 mA

87. 75.5 μA

88. 2.4 A

89. 0.6 A

90. 120 mA

91. 24 mA

92. 12 mA

93. 2.4 mA

94. 0.6 mA

95. 60 μA

96. *

97. *

98. *

99. *

100. True

101. *

102. Series

103. Parallel

104. *

105. *

106. *

107. *

108. False

109. True

110. *

111. *

112. True

113. False

114. True

115. True

*Depends on the type of meter used.

EXPERIMENT 2-1

MEASURING RESISTANCE

Resistance is the term used to describe the opposition encountered by electric current flow. Resistance is measured in ohms (Ω). In unit 1, you learned how to determine the value of a resistor by examining its color bands. However, the resistance of many components cannot be determined through observation and therefore must be measured.

This lab is designed for an analog meter so that scale interpretation may be learned. Simple changes will easily allow use of a digital meter, if desired.

OBJECTIVE

To learn how to measure resistance with the ohmmeter portion of a multimeter.

EQUIPMENT

Multimeter (VOM)

Potentiometer: 5 kΩ

Resistors: 10 Ω, 15 Ω, 220 Ω, 470 Ω, 1 kΩ, 5.1 kΩ, 68 kΩ, 100 kΩ, 220 kΩ, 1 MΩ

PROCEDURE

1. The multimeter, or VOM, is the meter most often used for basic electronics work. A VOM can be used as an ammeter, a voltmeter, or an ohmmeter. Simply adjust the function-select switch for the desired function. Fig. 2-2 shows the controls, including the function-select switch, of a common VOM.

The function-select switch is in the center of some circular divisions and acts as a dial. A portion of the circular divisions is designated the ohms function. The area of the divisions located within the ohms-function space is divided into four positions: × 1, × 100, × 1000, and × 1 00,000. The meter you are using may be slightly different from the one illustrated. Nevertheless, it exhibits the same basic characteristics as the VOM shown. Adjust the function-select switch on your meter to the ohms function. List the different positions in the ohms-function area on your meter._____

2. Now that you have adjusted the VOM to the ohms function, connect the test leads to the meter. The test leads used with the VOM usually are red and black. The colors are used to help you differentiate the positive and negative polarities of the meter. For our purposes red indicates the positive polarity (+), and black indicates the negative (–) polarity. Look at the meter controls in Fig. 2-2. In your VOM insert the red test lead into the hole or jack marked with (+) and the black test lead into the hole or jack marked with (–). (Note:The meter you are using may be different from the one illustrated. If this is so, plug the red and black test leads into the appropriate jacks and proceed.) Touch the test leads together. Describe what happens to the needle located on the scale of the meter._______

3. You have now adjusted the function-select switch to the ohms function of the VOM, inserted the proper test leads into the proper jacks, and seen that when the test leads are touched together, or shorted, the needle of the meter moves from the extreme left-hand side of the meter scale to the extreme right-hand side. If you are using a DVM, the display will indicate 0. When the leads are not touched together, the digit 1 will appear on the left display in most cases. The 1 indicates infinite resistance.

4. You should now become familiar with the scale of the meter. Fig. 2-3 is a scale of a very commonly used VOM. If you are using a DVM, skip this section.

The top scale (from 0 to ∞, labeled ohms) is used for measuring ohms only. On most VOMs, the top scale is designated as the ohms scale. Record the location and color of the ohms scale on your meter.

5. To measure any resistance in ohms, you must select the proper position or range. On the meter illustrated in Fig. 2-2, there are four ranges: × 1, × 10, × 1000, and × 100,000. The ohmmeter must be properly zeroed before any attempt is made to accurately measure resistance. To zero the ohmmeter, short the two test leads together. This should cause the needle to move from infinity (∞) on the left to zero (0) on the right. Infinity represents a very high resistance, whereas zero represents a very low resistance. If the needle does not reach zero or if it goes past zero when the test leads are shorted, the control marked ohms adjust must be used to adjust the needle to rest on zero when the test leads are touched together. There will be a similar adjustment on your VOM if yours is different from the one illustrated. Adjust the VOM to each of its ranges: × 1, × 10, × 1000, and × 100,000 and zero the meter for each of these ranges. The ohmmeter must be zeroed before each resistance measurement and after each range change. Otherwise your measurements will be incorrect.

6. The ohms scale on the meter is nonlinear. The divisions on the right side of the scale are farther apart than those on the left side. This provides a more accurate measurement of resistance when the needle of the meter deflects and stops somewhere between the center of the ohms scale and zero.
Choosing the proper range adjustment controls where the needle deflects. Adjust the function-select switch to the × 1 range of the ohms function. Zero the meter, and then connect it across a 10 Ω resistor. Record the precise resistance (in ohms) indicated by the needle on the ohms scale in Fig. 2-1A. The range selected for this operation was × 1, which means that the number to which the needle points will be multiplied by 1.

Figure 2-1A

7. Adjust the function-select switch to the × 100,000 range. Zero the meter and connect it to a 100 kΩ resistor, as illustrated in Fig. 2-1B. Record the resistance (in ohms) shown by the needle on the ohms scale. The range selected for this measurement is × 100,000, which means that the number to which the needle points will be multiplied by 100,000.

Figure 2-1B

8. Measure and record the values of the resistors indicated in Fig. 2-1C. Remember to choose a meter range that will cause the needle to deflect somewhere between the center of the scale and zero. Always zero the meter when changing ranges, and always multiply the number indicated on the scale by the multiplier of the chosen range: × 1, × 100, × 1000, × 100,000. Never measure the resistance of a component until it has been disconnected.

Figure 2-1C

9. Using the proper procedure for measuring resistance, measure and record the precise resistance of the 200 Ω pot illustrated in Fig. 2-1D.

Figure 2-1D

10. Adjust the control of the pot while the ohmmeter is connected. Describe how this action affects the measured resistance of the pot.______

11. Alter the connections of the pot as illustrated in Fig. 2-1E.

Figure 2-1E

12. Adjust the pot both clockwise and counterclockwise and describe how this action affects its measured resistance._____

ANALYSIS

1. Why is the ohms scale of an analog multimeter considered to be nonlinear? _____

2. Where on an analog ohms scale are the most accurate measurements found? _____

3. What is meant by the × 1000 range on the ohm meter? _____

4. What is meant by zeroing the ohmmeter? _____

5. Why is it necessary to zero the ohmmeter? _____

6. If the range of the ohmmeter was set to × 100,000 and the needle pointed to 0.6 on the ohms scale, what would be the value of the resistance being measured? _____

EXPERIMENT 2-2

MEASURING VOLTAGE

Voltage is the force that causes electric current to flow through conductors or paths. This force, sometimes called electromotive force (EMF), is measured in volts. It is essential that anyone involved in electronics work be able to use the necessary equipment to measure voltage accurately.

This lab is designed for an analog meter so that scale interpretation may be learned. Simple changes allow the use of a digital meter, if desired.

OBJECTIVES

1. To learn to measure voltage with a multimeter.

2. To construct basic electric circuits.

EQUIPMENT

Multimeter (VOM)

Potentiometer: 5 kΩ

Resistors: 470 Ω, 1 kΩ

6 V battery or power supply

6 V lamp with socket

Connecting wires

PROCEDURE

1. You learned in Experiment 2-1 that a multimeter can be used to measure resistance. A multimeter also can be used to measure voltage. Experiment 2-1 showed that the function-select switch can be adjusted to cause the multimeter to perform many measurement functions with several different ranges. The dc voltage ranges of the meter shown in Fig. 2-2 are 3, 12, 60, 300, 1200, and 6000 V. When the function-select switch is adjusted to 3 V on the dc volts range, the meter can be used to measure a maximum of 3 V. The same is true of the remaining ranges within the dc volts function. The numerical value of the chosen range indicates the maximum value of voltage that may be measured on that range. The meter you are using may differ somewhat from the VOM illustrated in Fig. 2-2. Nevertheless, it will exhibit the same basic characteristics as the one described.

2. Adjust the function-select switch on your meter to the lowest range of the dc volts function. List the different ranges within the dc volts function on your meter.
_____, _____, _____,
_____, _____

3. Connect the red and black test leads to the meter by inserting the appropriate ends into the proper jacks on the face of the meter. The red test lead should be inserted into the jack labeled (+) and the black test lead should be inserted into the jack labeled –COM. (Note: The meter you are using may be different. If this is the case, plug the red and black test leads into the appropriate jacks and proceed.)

4. You now have the VOM properly equipped and adjusted to measure dc volts. You should now become familiar with the portion of the scale of the meter used for measuring dc volts. Figure 2-3 shows the scale of a very commonly used VOM. The scale immediately under the ohms scale is the dc volts scale. There are three dc volts scales: 0 to 12 V, 0 to 60 V, and 0 to 300 V. All dc voltages are measured with one of these scales. The question becomes, What scales are to be used with what meter ranges? Each of the dc voltage ranges corresponds to a number on the right side of the meter scale or a multiple or divisor of that number. Figure 2-2A indicates the proper scale to be read for each dc voltage range.

5. When you choose the 12 V, 60 V, or 300 V range, you read the scale directly. In these ranges, the number to which the needle points is the actual value of the voltage being measured. When you select the 3 V range, the number to which the needle points must be divided by 100. For example, if the needle of the meter points to 50 while the meter is adjusted to the 3 V range, the measured voltage is 0.5 V. (Note: The meter you are using may differ slightly from the one described. VOMs usually have several scales. Some of these scales can be read directly, whereas others necessitate use of a multiplier or divisor. If your VOM is different, identify the scales that can be read directly and the ones that must be used with multipliers or divisors.)

6. Complete Fig. 2-2B by indicating the proper voltage scale and voltage value. Show the multiplier or divisor for the voltage range for the meter scale shown. This will give you practice using a meter scale.

7. You are now almost ready to measure dc voltage. Before actually doing so you should become familiar with some facts about choosing the dc voltage range. Recall from step 1 that the numerical value of the chosen range indicates the maximum value of voltage that may be measured on that range. When the range selected is 12 V, the maximum voltage that the meter can measure is 12 V. Any voltage above 12 V could damage the meter on this range. This is true for most voltage scales on most VOMs. If you are trying to measure a voltage that is totally unknown (no indications as to its approximate value), you should start the measuring procedure by choosing the highest range on your meter and slowly adjusting the range downward until a voltage reading is indicated on the upper or right-hand half of the meter scale. Complete Fig. 2-2C by showing the proper meter range to be selected, the proper meter scale to be read, and the proper multiplier and divisor to be used with each voltage to be measured. Use the scale of your meter to complete the figure.

8. You need to consider meter polarity when measuring dc voltage. Correct matching of meter polarity to voltage polarity is vital. If proper care is not exercised, the meter will deflect backward, and the internal components will be damaged. Meter polarity is simple to determine. The positive (+), red, test lead is connected to the positive side of the dc voltage to be measured. The negative (–), black, test lead is connected to the negative side of the dc voltage to be measured.

9. Measure and record the actual voltage of a 6 V battery. The voltmeter is always connected across the voltage, or in parallel with the voltage to be measured.
Actual voltage of battery = _____V

10. Construct the circuit illustrated in Fig. 2-2D. Measure and record the voltage supplied by the battery and the voltage across the lamp.

Figure 2-2D

11. A certain amount of voltage is always necessary to cause current flow. This voltage is called the voltage drop and is found across any component through which current flows. The polarity of this voltage drop is determined by the direction of the movement of electrons from negative to positive. Thus if electrons were moving through a resistor in the direction shown in Fig. 2-2E, the left side of the resistor would be negative (–) and the right side would be positive (+). The black test lead of the meter would be connected to the left side of the resistor and the red test lead would be connected to the right side. This procedure would measure the voltage drop developed across this resistor. In the illustrations of Fig. 2-2F, indicate the proper meter polarity for measuring the voltage drop across each resistor.

Figure 2-2E

Figure 2-2F

12. Construct the circuit of Fig. 2-2G. Measure and record the battery voltage and the voltage drops across R₁ and R₂. Remember that electrons move from negative to positive.

Figure 2-2G

13. Construct the circuit of Fig. 2-2H. Measure and record the voltage drops across R₁ and R₂.

Figure 2-2H

14. Construct the circuit shown in Fig. 2-21.

Figure 2-21

15. Adjust the potentiometer both counterclockwise and clockwise and record the voltages.
Counterclockwise voltage = _____V
Clockwise voltage = _____V

ANALYSIS

1. What is voltage? _____

2. If you were measuring an unknown voltage what meter range would you choose? Why? _____

3. What determines the polarity of a voltage drop developed by a resistor through which electrons are moving? _____

4. What causes the voltage drop developed across any component through which electrons are moving? _____

5. When is it necessary to use a multiplier or divisor with a scale on an analog multimeter? _____

6. How is the proper range of a multimeter selected? _____

7. Could 4 V be measured on the 3 V range of a multimeter? Why?

8. Indicate the proper range of your meter for measuring the following dc voltages:

EXPERIMENT 2-3

MEASURING CURRENT

Current is the movement of electrons from one location to another through conductors or paths. Current is measured in amperes (the number of electrons moving past a given point in a circuit per second), milliamperes (0.001 A), or microamperes (0.000001 A). It is essential that anyone involved in electronics work learn to measure current values accurately.

An analog meter is used in this activity so that scale interpretation can be learned. Simple changes allow the use of a digital meter, if desired.

OBJECTIVES

1. To learn to measure current with an ammeter.

2. To construct basic electric circuits.

3. To convert amperes to milliamperes or microamperes and vice versa.

EQUIPMENT

Multimeter (VOM)

Resistors: 220 Ω, 1 kΩ, 100 kΩ, 220 kΩ

6 V battery or power supply

SPST switch

Connecting wires

PROCEDURE

1. You have learned from previous experiments that a VOM can be used to measure resistance and voltage. In addition to these electric quantities, current can be measured with a VOM. Figures 2-2 and 2-3 show the controls and the scale of a common VOM. The function-select switch controls the measurement function and the range of the VOM. Figure 2-2 indicates that the function-select switch may be adjusted to one of five ranges within the dc function, namely, 12 A, 120 mA, 12 mA, 1.2 mA, and 60 μA. Thus when the function-select switch is placed in the 120 mA position within the dc function, the meter can be used to measure a maximum of 120 mA. The other dc current ranges of the VOM are similarly arranged. The numerical value of the chosen range shows the maximum value of current that can be measured on that range.

2. The meter you are using may differ somewhat from the illustrated VOM. It should, however, exhibit the basic characteristics of the one described. Adjust the function-select switch on your meter to the lowest range of the dc function. List the different ranges for measuring dc on your meter._____, _____, _____,_____, _____

3. Plug the black and red test leads into the jacks labeled (–) and (+), respectively. (Note: If your meter is different from the one illustrated, plug the test leads into the appropriate jacks and proceed.)

4. You are now ready to become familiar with the portion of the scale of the meter used for measuring direct current. Figure 2-3 illustrates the scale of a commonly used VOM. Three scales are used for measuring dc. They are the same as those used to measure dc voltage. Five dc ranges can be used with this meter. All current measurements are read on these scales with the proper multiplier or divisor. Figure 2-3A shows the proper multiplier or divisor to be used with the dc scales for any of the five ranges. (Note: Your meter may have different scales and multipliers from those in Fig. 2-3A. Identify them and proceed.)

5. Each range of dc has a specific multiplier or divisor or is read directly on the scale. For example, if the needle of the meter points to the number 6 on the dc scale, and the meter is adjusted to the 12 mA range, the measured current is 6 mA. If the needle points to 6 while the meter is adjusted to the 120 mA range, the measured current is 60 mA (6 × 10 = 60, or 6 ÷ 0.1 = 60).

6. Complete Fig. 2-3B by determining the proper current value when the needle points to a specific number. Also determine the correct multiplier and divisor to be used with the indicated current range. You should use the equivalent ranges, scales, multipliers, and divisors of the meter in Figs. 2-2 and 2-3.

7. Most VOMs can be used to measure currents greater than 1 A. Up to 12 A of current may be measured with the meter illustrated. The numerical value of the chosen range indicates the maximum value of current that can be measured in that range. For example, when the range selected is 12 mA, the meter can be used to measure a maximum of 12 mA. Any current above 12 mA could damage the meter in this range. This is true for most current scales of most VOMs. If you are trying to measure an unknown current (no indication of its approximate value), start the measuring procedure by choosing the highest range on your meter and slowly adjusting the range downward until a current reading is indicated on the scale. Complete Fig. 2-3C by indicating the proper meter range to be selected and the proper multiplier and divisor to be used with each value of current to be measured. (Note: Always select the smallest range that will allow you to measure the current.) Use your meter's ranges and scales for completing Fig. 2-3C.

8. Meter polarity of the VOM is important when measuring current. The VOM must always be connected in such a way as to allow the current to flow through the meter in the proper direction. Otherwise the needle will deflect backward, possibly causing internal damage to the meter. If current is to flow through the meter in the proper direction, consideration must be given to the direction of current. Current flows from negative to positive; thus if the meter is connected correctly into a circuit, current will flow through the black test lead (–), through the meter, and then through the red test lead (+). The illustration of Fig. 2-3D should be helpful.

Figure 2-3D

9. In the illustrations of Fig. 2-3E show which test leads should be red (+) and which should be black (–) for the current meters indicated.

Figure 2-3E

10. Adjust the VOM to the dc function 120 mA range (or equivalent) and connect it into the circuit, as illustrated in Fig. 2-3F. Be sure to observe the proper meter polarity.

11. Close the SPST switch and record the current indicated by the VOM: _____ mA, or _____ A.

12. Open the SPST switch and add the additional resistor illustrated in Fig. 2-3G.

13. Change the range of the VOM to 12 mA (or equivalent), and close the switch. Record the current indicated on the VOM: _____ mA, or _____ A.

14. Disconnect the circuit of Fig. 2-3G and connect the circuit of Fig. 2-3H.

15. Set the VOM to the 60-pA range (or equivalent), and connect the meter into the circuit, observing proper polarity. Close the switch and record the current: _____ μA, or _____ mA, or _____ A.

16. Disconnect the circuit illustrated in Fig. 2-3H.

17. Construct the circuit illustrated in Fig. 2-3I.

Figure 2-3I

18. Adjust the VOM to the 12 mA range (or equivalent) and connect it into the circuit illustrated in Fig. 2-3I, observing proper polarity. Record the current: _____ mA, or _____ A.

ANALYSIS

1. What is current? ______________________________________

2. What does each of the dc ranges on your multimeter indicate? _________________________________

3. Describe how a multimeter is properly connected into a circuit to measure current. _________________________________

4. Why is proper polarity important to observe when measuring dc current? _________________________________

5. What meter ranges would be selected on your meter to measure the following currents? _____

EXPERIMENT 2-4

FAMILIARIZATION WITH POWER SUPPLY

The variable dc power supply is an electronic circuit that changes alternating current (ac) into dc. This circuit is usually housed in a case or protective enclosure. Output jacks are provided for external connections. This type of power supply usually has some means by which the output voltage can be adjusted from zero (0) to a maximum value. The symbol for the variable dc power supply is illustrated in Fig. 2-4A.

Figure 2-4A

OBJECTIVE

To become familiar with the use of a power supply to provide dc voltage to an electronic circuit.

EQUIPMENT

Multimeter (VOM)

1.5 V dry cell

Variable dc power supply

Resistor: 100 Ω

PROCEDURE

1. A dry cell or battery can be used as a simple power source for a circuit. Acquire the 1.5 V dry cell and prepare the VOM to measure dc voltage. Measure and record the precise voltage across the cell: _____ V.

2. Construct the circuit illustrated in Fig. 2-4B.

3. The circuit represents a dry cell in a loaded state (large current output). Measure the dry cell voltage with it loaded as shown in Fig. 2-4B: _____V.

4. How did the voltage measured in step 1 compare with the measured voltage in step 3? How do you account for any difference? _________________________________

5. In Fig. 2-4C, make a simple sketch of the variable dc power supply that you will use for this and future experiments. Include in your sketch all controls, output jacks, and range switches, where applicable.

6. A common type of power supply is shown in Fig. 2-4D.

7. Adjust the VOM to measure dc voltage. Connect it to the dc output jacks of the power supply. These are usually labeled (+) and (–) or ground.

8. Turn on the power supply and adjust it to produce maximum dc voltage. Record the maximum voltage measured on the VOM.
Maximum voltage = _____ V.

9. Adjust the variable dc voltage control on the power supply to cause it to produce different voltages measured with the VOM. What is the voltage range of your power supply?
Range = _____V to_____V.

10. Turn off the power supply and disconnect the VOM.

11. If the power supply operating instructions are available, read them thoroughly.

ANALYSIS

1. Why is it considered correct to check the condition of a dry cell while it is loaded? _________________________________

2. What are some advantages of using dry cells? _________________________________

3. What are some advantages of using a variable dc power supply? _________________________________

4. Draw the symbols for a dry cell and a variable dc power supply.

5. What is meant by the term ground? _________________________________

6. Draw the symbol for a ground.

Unit 2 Examination

Measuring Voltage, Current, and Resistance

Instructions: For each of the following, circle the answer that most correctly completes the statement.

1. A VOM is an example of a

a. Multifunction meter

b. Single-function meter

c. Galvanometer

d. High-resistance meter

2. For measuring voltage, the meter is connected in

a. Series

b. Parallel

c. Series-parallel

d. Either series or parallel

3. For measuring current flow, the meter is connected in

a. Series

b. Parallel

c. Series-parallel

d. Either series or parallel

4. The ohmmeter setting that would be best when checking the continuity of a fuse is:

a. R × 1

b. R × 10

c. R × 1000

d. R × 100,000

5. The current indicated on the analog meter scale of Figure 2E-5 is

a. 5 A

b. 25 A

c. 5 mA

d. 25 mA

Figure 2E-5

6. When measuring resistance with an ohmmeter, a short indicates

a. Infinite resistance

b. Zero resistance

c. Midscale resistance

d. Cannot measure a short with an ohmmeter

7. The current indicated on the meter scale of Figure 2E-7 is

a. 100 mA

b. 200 mA

c. 10 mA

d. 2 mA

Figure 2E-7

8. The current indicated on the analog meter scale of Figure 2E-8 is

a. 40 A

b. 8 A

c. 40 mA

d. 8 mA

Figure 2E-8

9. The current indicated on the analog meter scale of Figure 2E-9 is

a. 5 mA

b. 25 μA

c. 25 mA

Figure 2E-9

10. A major precaution to observe when measuring resistance with an ohmmeter is to make sure

a. Circuit power is turned off

b. Circuit power is turned on

c. Range switch is set on maximum setting

d. Polarity is observed

True-False: Place either T or F in each blank.

___11.	When using a multimeter to measure dc voltage, polarity should be observed.
___12.	Ohms adjust should be used each time the resistance range is changed.
___13.	For measuring current flow, the meter should be connected in series.
___14.	For measuring volts, the meter should be connected in parallel.
___15.	The most accurate ohms reading of an analog multimeter is found on the left side of the ohms scale.
___16.	Polarity is important when measuring ac volts.
___17.	Polarity is not important when measuring resistance.
___18.	For measuring a resistor valued at 10 Ω, the × 1 scale of an ohmmeter should be read.
___19.	It is considered good practice to measure the resistance of a circuit with voltage present in the circuit.
___20.	When measuring an unknown value of dc voltage, one should start at the highest range and work down to the correct range.