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ELEC 103 LABORATORY EXERCISE 1 USE OF THE MULTIMETER PURPOSE OF EXPERIMENT The purpose of this experiment is to determine the resistance of two circuit components, light bulb #1 and light bulb #2. In this experiment, you will determine the resistance of the light bulb's by measuring the current flowing through each bulb and the voltage drop across each bulb. Then Ohm's Law will be used to calculate the resistance of each bulb by dividing the voltage measured across the light bulb by the current measured flowing through the light bulb. EQUIPMENT LIST 1 DC Power Supply 2 6V Light Bulb's 1 Simpson Model 260 VOM PROCEDURE PART 1 1. Carefully examine the Simpson Model 260 multimeter and note the location and configuration of the following controls and scales: RANGE/FUNCTION SWITCH is located in the center of the control panel. It has 12 positions including five positions for voltage. They are oriented to the left. Four positions for current are located across the top and upper right. And three positions for resistance located to the right. STATUS/POLARITY SWITCH is located on the left side of the control panel. This switch usually has an off or transport position, a +DC position, a DC position, and an AC position. ZERO OHMS ADJUST KNOB is located on the right side of the control panel. This knob is used to adjust the meter pointer to zero ohms on the resistance ranges when the meter leads are connected together. DC SCALE is the second scale down from the top under the glassed portion of the multimeter. It is sometimes located directly under the parallax mirror. This scale is used for all DC voltage and current ranges. The scale is divided into 50 divisions and is similar to the scale used in the figures during your Unit One learning experiences. When using the 2.5 volt range switch position and when using the 500 volt range/function switch position, you must mentally move the decimal point to the appropriate position. On all other range switch positions the numbers on the scale are appropriate. COMMON () AND PLUS (+) RECEPTACLES are located in the lower left corner of the control panel. Always make certain the black lead is connected to the minus or negative receptacle and the red lead is connected to the plus or positive receptacle. Page 1 ELEC 103 LABORATORY EXERCISE 1 USE OF THE MULTIMETER PROCEDURE PART 2 NOTE: It is not always possible to determine the approximate value of the current flowing in a circuit before you measure it with the milliammeter. Therefore, when the milliammeter is connected in series with the element you should start with the range switch adjusted to the highest current measuring range. After power has been applied to the circuit, adjust the range switch to lower current ranges until you obtain an appropriate current measurement. If the meter pointer moves to the left, reverse the meter leads and continue with the experiment. 1. Connect the circuit as shown in Figure 11. Be certain to connect the milliammeter to the circuit so it is connected in series with the circuit. Additionally, connect the meter to the circuit observing correct polarity. The negative lead of the milliammeter is connected toward the negative or ground side of the power source, and the positive lead is connected toward the positive side of the power source. Use the highest current range possible. 2. Close the switch. (Turn the switch on.) You should see no current flow indicated by the meter pointer since you are on a very high current range. Adjust the range/function switch to the next lower current measuring range position. Continue doing this until the meter pointer moves up scale when you have adjusted the range/function switch to a lower range. Your reading on the meter will tell you if it is safe to go to the next lower scale. For example, if the meter pointer shows a reading of 15 milliamperes when it is Figure 11 on the 100 milliampere range, then it would NOT be safe to go to the 10 milliampere range. CONCLUSION The resistance of a component can be determined by calculation when the voltage across the component and the current through the component has been measured. NOTE: The resistance of the bulb is different when the bulb is HOT than when it is cold. The resistance of the bulb cannot be measured directly when it is hot and has current flowing through it. However, the resistance of the bulb's filament can be determined indirectly using the voltage and current measurements, and Ohm's Law as was done in this experiment. Page 2 ELEC 103 LABORATORY EXERCISE 1 USE OF THE MULTIMETER DATA TABLES 4. 5. 6. Record the current you measured in step 3 in the box to the right. It = ____________ mA Measure the voltage across light bulb #1 and record it as V1. The correct polarity must be observed when connecting the voltmeter to the circuit. V1 = ___________ V Measure the voltage across light bulb #2 and record it as V2 The correct polarity must be observed when connecting the voltmeter to the circuit. V2 = ___________ V 7. Calculations using Ohms Law: R1 = Volts Amps R2 = Volts Amps = 8. Calculations using Ohms Law: Page 3 = R1 = ____________ R2 = ____________