Experiment 1: Ohm's Law

In this experiment, you will apply Ohm's Law to investigate the relationship between voltage, resistance and current.

Materials

4 AA Batteries

2 Alligator Clips

Digital Multimeter

Masking Tape

Permanent Marker

1k? Resistor from Snap Circuit Kit

Ruler

Procedure

1. Prepare the digital multimeter by inserting the black cord into the "COM" port and the red cord into the "V?mA" port in the bottom right corner. You will be using multiple functions of the multimeter. The two main sections you will be using in this procedure are "DCV" located in the top left and "DCA" located on the right and "?" located on the bottom right (Figure 3).
2. Turn the multimeter on using the switch under the dial.
3. Turn the dial of the multimeter until the arrow points to the "20" in "DCV".
4. Tear off four square pieces of masking tape from the roll and place one on each battery. Use the permanent marker to label the batteries 1 - 4.
5. Tear off a 20 cm long piece of masking tape and set the non-sticky side down on the table.
6. Place Battery 1 on the masking tape such that the positive side of Battery 1 is located at the left end of the length of masking tape.
7. Use the multimeter to measure the voltage of Battery 1 by touching the metal probe of the red cord to the positive side of the battery and the metal probe of the black cord to the negative side of the battery. Record the voltage in Table 2.
8. Note: Reversing the cords and battery ends causes the multimeter to read a negative voltage.
9. Place Battery 2 on the masking tape so that the positive side of Battery 2 to touches the negative side of Battery 1 (Figure 4). Use the multimeter to measure the voltage of Battery 1 and 2. Record the voltage in Table 2.
10. Place Battery 3 on the masking tape so that the positive side of Battery 3 to touches the negative side of Battery 2. Use the multimeter to measure the voltage of Battery 1, 2, and 3. Record the voltage in Table 2.
11. Place Battery 4 on the masking tape so that the positive side of Battery 4 to touches the negative side of Battery 3. Use the multimeter to measure the voltage of Battery 1, 2, 3 and 4. Record the voltage in Table 2.
12. Remove Batteries 2, 3, and 4 from the masking tape.
13. Turn the dial of the multimeter so the arrow points to the "20m" in the "DCA". The "m" stands for the suffix "milli".
14. Use one alligator clip to connect the positive side of Battery 1 to one end of the 1k? resistor.
15. Use the other alligator clip to connect the other side of the resistor to the red probe of the multimeter.
16. Touch the metal probe of the black multimeter cord to the negative side of the battery. You have now completed a circuit and should have an electric current reading on your multimeter. Record the current in Table 2. Since the scale is in milliamps, you will need to convert your number to amps (1 amp = 1000 milliamps)
17. Add battery 2 as you did in step 8 and repeat steps 15. Record the current in Table 2.
18. Add battery 3 as you did in step 9 and repeat steps 15. Record the current in Table 2.
19. Add battery 4 as you did in step 10 and repeat steps 15. Record the current in Table 2.
20. Remove the alligator clips from the battery, resistor, and multimeter.
21. Turn the dial on the multimeter to "2000" in the "?" section. Place the red and black probe on opposite sides of the resistor to measure its resistance. Record this value in Table 3.

Experiment Resistance of Play-DohR Experiment Inventory Materials Labware 3 Alligator Clips Ruler 2 AA Batteries Vernier Calipers AA Battery Holder Digital Multimeter Play-DohR *Scissors Aluminum Foil You must provide items marked in *red EXPERIMENT 2: RESISTANCE OF PLAY-DOHR In this experiment, you will experimentally determine how area and length affect resistance using Play-Doh@. PROCEDURE Part 1: Relationship between Resistance and Length 1. Prepare the digital multimeter by inserting the black cord into the "COM" port and the red cord into the "VQmA" port in thebottom right corner. You will be using multiple functions of the multimeter. D 2. Turn the multimeter on using the switch under the dial. D 3. Turn the dial of the multimeter until the arrow points to the \"20' in \"DCV.\" |:|4. Place two AA batteries into the battery holder so that the negative ends of the batteries touch the spring end of the battery holder. E] 5. Measure the voltage across the two batteries by touching the metal probes ofthe multimeter to the metal knobs on the battery holder. Record this value in Table 4. [:J 6. Use scissors to carefully cut two 4 x 4 cm squares from the aluminum foil. [:1 7. Starting at one side of one foil square. roll (or fold} the foil into a rod. Squeeze the rod between your ngers after you have rolled it to get it firmly packed. Note: This step is important because the foil will be used to conduct a current. E] 8. Repeat Step 7 for the second foil square. '3 9. Roll out the PIayDoh into a cylinder with a length of 20 cm and a uniform diameter of approximately 1015 mm. I] 10. Use the Vernier caliper to measure the diameter of the cylinder every ve centimeters to check for uniformity. Record the average radius (half the diameter) in Table 4. I] 11 . Create a circuit by pushing one aluminum foil rod through one end of the cylinder so that the foil rod is perpendicular to cylinder and the ends of the foil stick out of the cylinder (Figure 6, next page). Place the ruler above the cylinder with the aluminum foil rod at the 0 cm mark. Figure 6: Circuit diagram. D 12. Use one alligator clip to connect the aluminum foil rod in the cylinder to the positive end of the battery holder (indicated by a \"+" sign). D 13. Connect the negative side of the battery holder (indicated by a \"-" sign) to the metal probe of the black cord of the multimeter with the second alligator clip (Figure 6). I: 14. Connect one end of the third alligator clip to the metal part of the red cord. The free end will be used to connect and disconnect the circuit. I: 15.Tum the dial on the multimeter to \"20m\" on 'DCA' section. I: 16. Push the second aluminum foil rod through the far end of the cylinder (the maximum distance) so that the foil rod is perpendicular to the cylinder and the ends of the rod are exposed. I: 17. Use the ruler to measure the distance between the aluminum rods. Record this value in meters in Table 5. D 13. Complete the circuit by connecting the free alligator clip to the second aluminum foil rod. Record the rst value for the current you see on the multimeter after about ten seconds in Table 5 and disconnect the alligator clip. It is important to not let the current flow through the Play-Dom for too long. D 19. Repeat Step 18 a few more times to make ensure consistent results. If the results are not consistent report the average current for a few trials. 20. Take the second aluminum rod out and move it two centimeters closer to the first aluminum rod. Repeat Steps 18 - 20 until the distance between the aluminum foil rods is has reached six centimeters. 21. Disconnect the circuit after all data has been collected. Note: Table 5 won't be completed until you finish the Post-Lab Questions. Part 2: Relationship between Resistance and Area 1. Prepare the digital multimeter by inserting the black cord into the "COM" port and the red cord into the "VOmA" port in the bottom right corner. You will be using multiple functions of the multimeter. 2. Turn the multimeter on using the switch under the dial. 3. Turn the dial of the multimeter until the arrow points to the "20" in "DCV." 4. Place the two AA batteries into the battery holder and measure the voltage across the two batteries. Record this value in Table 6. 5. Use scissors to carefully cut two 4 x 4 cm squares from the aluminum foil. 6. Starting at one side of one foil square, roll (or fold) the foil into a rod. Squeeze the rod between your fingers after you have rolled it to get it firmly packed. Note: This step is important because the foil will be used to conduct a current. 7. Repeat Step 6 for the second foil square.El 8. Roll out Play-Doh into a cylinder of length 101 2 cm and a diameter of approximately 101 5 mm. Use the Vernier caliper to measure the diameter of the cylinder every two centimeters to check for uniformity. Record the radius in Table 7. I] 9. Create a circuit by pushing one aluminum foil rod through one end of the cylinder so that the foil rod is perpendicular to cylinder and the ends of the foil stick out of the cylinder (Figure 6). Place the ruler above the cylinder with the aluminum foil rod at the 0 cm mark. I] 10. Use one alligator clip to connect the aluminum foil rod in the cylinder to the positive end of the battery holder (indicated by a \"+" sign). I] 11. Connect the negative side of the battery holder (indicated by a \"-' sign) to the metal probe of the black cord of the multimeter with the second alligator clip. [I 12. Connect one end of the third alligator clip to the metal part of the red cord- The free end will be used to connect and disconnect the circuit. [:1 13. Turn the dial on the multimeter to '20m" on \"DOA.\" D 14. Push the second aluminum foil rod through the far end of the cylinder {the maximum distance) so that the foil rod is perpendicular to the cylinder and the ends of the rod are exposed. I] 15. Use the ruler to measure the distance between the aluminum foil rods. Record this value in meters in Table 6. Keep this value constant for all areas. [:I 16. Complete the circuit by connecting the free alligator clip to the second aluminum foil rod. After about 10 seconds, obtain a quick reading (you don't want the current to go through the Play-Dom cylinder for too long). [:l 17. Repeat Step 16 a few more times to make ensure consistent results. If the results are not consistent report the average current for a few trials. Record the current in Table 7 (1 amp = 1000 milliamps). [:I 18. Disconnect both alligator clips from the aluminum and remove the aluminum rods for the Play-Dom cylinder. [:I 19. Remold the PIayDoh to create a cylinder of the same length. 8-10 cm. but a different area (diameter). D 20. Choose three new areas ranging from 0.5-3 cm in diameter. 21. Use the Vernier caliper to make sure the cylinder is uniform in diameter over its length. 22. Replace both aluminum rods making sure they are the same distance away from each other as they were in Step 15. 23. Connect the alligator clips to the aluminum. 24. Repeat Steps 16-23 for three additional cylinder areas. Note: Table 7 won't be completed until you finish the Post-Lab Questions.Table 4: Cylinder Length Circuit Data Length [In] Current [A]: Table 5: Length and Resistance Circuit Data Length {m} Current [A] Resistance {} Table 6: Cylinder Area Circuit Data Length [In] Current {A} Table T: Resistance and Area Circuit Data Radius [m] Current [A] Resistance {0; . Plot a graph of Table 2. Construct your plot on a oomputer program such as Microsoft Exoel. If you do not have a graphing program installed on your computer, you can aooess one on the internet via the fol- lowing links: htlpnoesedgovfnceskiddcreateagrapw or httijwwnnlinedtarttooLoomtgraph? selected _graph=bar. . What is the relationship between vortage and current? Use data from your graph to support your answer? _ Determine the slope of the line and record it in Table 3. _ How does the value of the slope compare to the resistance you rneasmed? Calculate the percent differ EDGE. . Use the results of your experiment to verify Ohm's Law. _ Howr does adding more batteries affect the power dissipated rough the resistor? Support your answer mathematically and record your answer in variable fon'n. Resistance (Q) Slope (VIA) % Difference 1 and 2 1, 2 and 3 1, 2, 3 and 4 Table 3: Resistor Data Resistance (Q) Slope (VIA) % Difference