PHY 112L Activity 2 Electronics Primer

Transcription

1 PHY 112L Activity 2 Electronics Primer Name: Section: ID #: Date: Lab Partners: TA initials: Objectives 1. Introduce the power supply and multimeter commonly used to analyze electric circuits 2. Understand how to measure voltage and current with a multimeter 3. Introduce the computerized equivalent of these devices (DataStudio functions) 4. Understand how to measure voltage and current with Pasco voltage and current sensors 5. Compare the voltage measurements made with different tools (Lab report) Materials & Resources 1. DC power supply and multimeter 2. Computer with DataStudio software 3. Pasco voltage and current sensors Introduction To experiment with the basic ideas of electricity, you need to be familiar with the tools most commonly used to measure electrical quantities and to analyze circuits. The additional skills you learn here will be beneficial in future labs since many procedures in later experiments will require more practical knowledge that is often not covered in lecture. In this activity, you will practice making basic circuit connections, using a multimeter to measure voltage and current, using a Pasco voltage sensor to measure voltage, and using a Pasco current sensor to measure current. Note that using the Pasco sensors to make these measurements allows you to save your results on the computer and print t hem out for later use such as when writing lab reports, but this cannot be done when using the multimeter. There are two types of power supplies: DC (Direct Current) and AC (Alternating Current). A DC power supply provides steady electricity, like a battery, and an AC power supply provides constantly changing electricity, like a wall outlet. In today s lab, we will only be using a DC power supply The multimeter is a tool that is capable of measuring multiple quantities, such as the resistance of a resistor, the voltage across a particular circuit element, or the current through a given part of a circuit. As such, a multimeter has modes for these different types of measurements. The symbols labeled on the multimeter are,, V, and A. These symbols represent the SI units, and designate the multimeter modes, for resistance, voltage, and current, respectively. Note that there are two sets of V and A symbols on the multimeter, each having flat or wiggly lines near them, which represent DC and AC measurements, respectively. In this lab, we will only be using the DC modes, or the V and A with the flat lines next to them. Although, as mentioned above, multimeters can be used to measure resistance, voltage, and current, these measurements must be made in a very specific way. In addition to selecting the correct mode, as described above, the connections must also be made correctly. To measure resistance or voltage, the black probe needs to be plugged into the COM port on the multimeter, while the red probe should be plugged into the and V port. Then, the measurement probes must be connected in parallel with the circuit element to be measured, as in Figure 1 below. However, to measure the current at a given point in a circuit, the red probe must be moved to the A or ma port on the multimeter and the measurement probes must be connected in series at the point in the circuit that you want to measure the current, as in Figure 2 below. Since voltage and current measurements can only be correctly made when the measuring device is connected as described above, be sure to connect the Pasco voltage sensor in parallel and the Pasco current sensor in series as well. 1

2 Resistor Voltage sensor Resistor Current sensor DC Power Supply DC Power Supply Figure 1 Figure 2 1. Multimeter, Power Supply and Pasco Interface 1) Verify that the power supply is turned off. 2) Connect the multimeter to the power supply as shown in Figure 3. 3) Select the multimeter mode for measuring DC Voltage. 4) Turn the power supply on and change the output voltage to each of the voltages listed in the table below. For each voltage, measure the output with the multimeter and record the results in the table below. 5) When all measurements have been made, turn off the power supply and disconnect the multimeter from the power supply. - + Figure 3 Multimeter reading when connected to Power Supply Voltage settings for Power Supply, then DataStudio with Pasco Interface 1 V 2 V 3 V 4 V 5 V Multimeter reading when connected to Pasco Interface 6) Connect the multimeter to the Pasco interface as shown in Figure 4. 7) Set the multimeter to DC Voltage mode. 8) Start DataStudio and click Create Experiment 9) Select the voltage output channel of the Pasco interface by clicking the circle indicated by the arrow in Figure 5. 10) Select DC Voltage from the drop-down in the Signal Generator. 11) Click auto and then on when you are ready to measure. 12) Change the amplitude of the output voltage to each value listed in the table above. Measure the output with the multimeter; record the results above. 13) Click off once all measurements have been made. Figure 4 Figure 5 2

3 2. Current Measurement 1) Create a new DataStudio project by clicking File, New Project, and then Create Experiment. 2) Set the multimeter to Current mode. 3) Connect the equipment as shown in Figure 6. 4) Select the voltage output channel (see Figure 5), then select DC Voltage in the Signal Generator. Set the Amplitude to 5.0V, then click auto and on when ready to begin. 5) Record the current from the multimeter below. I M = A 6) Click off to turn off the current output and then disconnect the leads from the multimeter. Note: leave all other connections in place. They will be reused for the second part of this experiment. 7) Connect the current sensor to port A of the Pasco interface, and then connect the leads that were previously connected to the multimeter to the red and black jacks of the current sensor as shown in Figure 7. 8) In DataStudio, click on channel A and select Current sensor in the window that pops up. Double click Digits in the Display menu and select current sensor as the data source, as shown in Figure 8. This creates a digital display for the current readings. 9) Click Start and record the measurement below. I P = A 10) Stop the experiment as before and disconnect all of the equipment. 11) Calculate the % difference between I M and I P. Show your work in the space provided below. Interface Figure 6: Current Measurement with Multimeter A % diff = I M I P = = % 2 (I M+I P ) Question: Since % error tells you how much your results differ from an accepted value, what does a % difference calculation tell you about your values here, I M and I P? Figure 7: Current Measurement with Pasco Sensor 2. Double click here to select current display 1. Click here to select channel A Figure 8 3

4 3. Voltage Measurement (Lab Report) 1) Create a new DataStudio project by clicking File, New Project, and then Create Experiment. 2) Set the multimeter to DC Voltage mode. 3) Connect the equipment as shown in Figure 9. 4) Select the voltage output channel (see Figure 5), then select DC Voltage in the Signal Generator. Set the Amplitude to 5.0V, then click auto and on when ready to begin. 5) Record the voltage measurement below: V M = V 6) Stop the experiment and disconnect the multimeter from the resistance module, but leave the connections between the module and the Pasco interface (Positive to J 2, Negative to J 1 ). 7) Connect the voltage sensor to port A, with its black lead connected to J 1 and red lead to J 2 as shown in Figure 7. 8) In DataStudio, click on channel A and select Voltage sensor in the window that pops up. Double click Digits and select voltage sensor as the data source. This creates a display for the voltage sensor readings. 9) Click Start; record the measurement below. V P = V 10) Stop the experiment as before and disconnect all of the equipment. 11) Calculate the % difference between V M and V P. Show all work in the space below. Figure 9: Voltage Measurement with Multimeter A Interface % diff = V M -V P = = % 2 (V M+V P ) Figure 10: Voltage Measurement with Pasco Sensor 4

5 Questions: 1) What does this % difference tell you about your measured values V M and V P in this case? 2) How would you connect a multimeter to the circuit shown in Figure 11 to measure the current through the resistor R 1? Clearly circle the circuit location where the multimeter leads should connect in order to make this measurement. Give the name and symbol for which multimeter mode should be used? R 1 R 2 Figure 11 3) How would you connect a multimeter to the circuit shown in Figure 12 to measure the voltage across the resistor R 2? Clearly mark with an X the circuit locations where the multimeter leads should connect in order to make this measurement. Give the name and symbol for which multimeter mode should be used? R 1 R 2 Figure 12 4) For both current and voltage, how does the measured value change if you swap the red and black leads? 5