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LAB 5 MEASURING VOLTAGES May 2, 2017 Lab 5 Set-up and Figure 1 1 LAB 5 MEASURING VOLTAGES May 2, 2017 OVERVIEW: Voltage measures potential difference, which causes electrons to move through a completed circuit. Current is the rate of flow of these electrons. The power source in a circuit provides the voltage. Polarity describes the orientation of the positive (+) and negative (-) terminals of a power source or measuring device used in a circuit. Electrons move through a circuit in two ways. Direct Current (DC) moves in only one direction, and is the result of a constant polarity power source such as a battery. Alternating current (AC) moves in two opposite directions, in a regularly alternating pattern. AC is the result of a power source with changing polarity, such as an AC generator. Batteries are voltage sources that derive their energy from a chemical reaction. Batteries can be connected together to increase or decrease the total voltage of the power source. To increase voltage, the positive terminal (cathode) of one battery is connected to the negative terminal (anode) of the next battery. (Fig. A) If you reverse the polarity of one of the batteries, that battery opposes the others, and lowers the total voltage. (Fig. B) Figure A . Figure B Batteries may also be connected in parallel. They must be equal in voltage. The voltage is not increased, but each battery supplies only part of the current, so they will last longer. 2 LAB 5 MEASURING VOLTAGES May 2, 2017 OBJECTIVES: A) Measure AC and DC voltage sources using an analog meter. B) Measure voltage sources using a digital multi-meter (DMM) C) Connect batteries together to increase or decrease voltage. EQUIPMENT REQUIRED: Snap leads for 9-Volt Battery Analog Multi-meter with probes Digital Multi-meter with probes Circuit Panel Easel Universal Lead Set 9-Volt battery Three 6-Volt batteries PROCEDURE: All voltage measurements will be taken with both the analog and the digital multi-meter, using the probe connectors. A) MEASURING AC VOLTAGE SOURCES 1. Set the analog multi-meter function switch to AC Volts. Set the range switch to 250 V or 300 V. Connect the black probe to the "common" (negative) connection, and the red probe to the positive (+) connection. WARNING: Do not touch the probe tips together when measuring the wall outlet voltage. Use the analog meter to measure the voltage of the wall outlet as shown in Figure 4. Record the reading in Data Table 1. 2. Set the digital multi-meter (DMM) function switch to AC. Set the range to 200 V. Connect the black probe to the "com" connection (common or ground) and the red probe to the "V.0" connection. Turn the meter to "on", and measure the wall outlet voltage. Record the reading, and turn the meter to "off". Always turn the meter off when it is not in use. B) MEASURING DC VOLTAGE SOURCES 1. Set the function switch of the analog meter to "+DC", and set the range switch to 10 or 12 V. Measure the voltage of a single 9 V battery as illustrated in Figure 5. Record the reading in Table 2. Repeat for a single 6 V battery. 3. Set the function switch of the DMM meter to DC and the range control to 20 V. With the DMM, measure the voltage of both the 9 V and the 6 V batteries. Record the voltage in Data Table 1. 3 LAB 5 MEASURING VOLTAGES May 2, 2017 C) MEASURING THE VOLTAGE OF BATTERY COMBINATIONS 1. Connect together three 6 V batteries as shown in Figure 6. These three batteries are connected in series. Set the range control of the analog meter to 25 or 30 V, and measure the voltage of the three batteries as indicated. Record the voltage as Battery Combination #1 in Data Table 2. 2. Use the DMM, still on the 20 V-setting, to measure the .same battery combination. 3. Reverse the polarity of battery 3, as shown in Figure 7. Measure the voltage, and record the results as combination #2 in Data Table 2. 4. Connect the snap leads to the 9 V battery. Remove battery #3 from the circuit, and replace it with the 9 V battery. Use the circuit panel as shown in Figure 8. Be sure that the polarity of each battery is the same as in the figure. Measure the voltage and record the results as combination 3 in Data Table 2. 5. Reverse the polarity of the 9 V battery. See Figure 9. Measure the voltage and record the results as combination #4. 6. Remove the leads from the batteries and disassemble the equipment. Be sure to turn the DMM to "off" before storing. ANALYSIS: Discuss the questions on the back of the lab form with your partners, and fill in the answers that you agree upon. If you cannot agree on a specific question, ask for help from the instructor. 4 LAB 5 MEASURING VOLTAGES Supervisor: ________________ OBJECTIVES: May 2, 2017 Recorder: ______________ Tech: ________________ Date__________ SKETCH OF LAB SET-UP: TABLE 1 Analog Multimeter Digital Multimeter Source Voltage Reading VA Switch Settings Function Switch Range Switch (volts) Voltage Reading VB Switch Settings Function Switch Range Switch (volts) Wall Outlet 9-V Battery 6-V Battery 5 LAB 5 MEASURING VOLTAGES May 2, 2017 DATA TABLE 2 Battery Comb. Analog Multimeter Voltage Reading VA Switch Settings Function Switch Digital Multimeter Voltage Reading VB Range Switch (volts) Switch Settings Function Switch Range Switch (volts) 1 2 3 4 LAB #5 ANALYSIS: 1. A voltage with constant polarity (positive or negative) is called ______________________________ 2. A voltage that changes polarity in a regular fashion is called ______________________________ 3. Explain what range setting should be chosen to avoid damaging the voltmeter when measuring an unknown voltage: ____________________________________________________________ 4. Show a schematic diagram indicating 1.5 V batteries in series that will provide 4.5 volts: 6 LAB 5 MEASURING VOLTAGES May 2, 2017 5. Show schematic diagrams of two different combinations of 1.5 V, 6 V, and/or 9 V batteries in series which will produce a total of 18 volts. (Don't use reverse polarity for either combination.) 6. Show a schematic diagram with three 1.5 volt batteries in parallel. A) What is the total voltage?___________ B) What advantage is obtained from connecting batteries in parallel? 7