Introduction In this lab, we will use measurements of voltage and current to determine resistance using Ohm's law, V=IR. We will rst measure the resistance of a single resistor. We will then measure how resistances combine in series and in parallel. Finally, we will look at the behavior of the resistance of a light bulb. "War was. these! Back to Top . 1 DC Power Supply Valuuztu \"mm\" Power Supply 0 1 Voltmeter ' . 1 Ammeter . 1 Resistor Board - 7 Banana Cables . 8 Alligator Clips . 1 Ohmmeter/Multimeter [per room] .. - Record data in this Google Sheets data table _ , _- Back to Top Procedure Over the course of the lab, your TA will be going around measuring resistances of your resistors with a multimeter (or they may be provided ahead of time). Record those resistances on your data sheet (in part 1; part II/III will copy automatically) when they do so. Click here for advice on NOT burning out the fuse in your ammeter. The simpler power supplies only have one knob, which will be what you control your voltage with in this experiment. There are also three-knob power supplies, which are not much more complicated, but you have to know what knob does what. Click here if you have a three-knob power supply. First, turn the rightmost knob ("Current") all the way to maximum, and leave it like this for the rest of the experiment. The switch on the upper-right doesn't matter. You'll be working with the other two knobs, which adjust voltage. The left knob is a "coarse" adjustment (to get you to the right ballpark), and the right knob is a "ne" adjustment (to tweak the voltage output). Use accordingly. All voltages should be read off the digital voltmeter, not the analog display on the power supply. Part 1': Measuring the Resistance of a Single Resistor First, choose a resistor to measure (R1 or R2), and record which one you chose on your data sheet. Then, wire the circuit up as shown below: 2 Animater Power Supplyi Click here for step-by-step instructions for setting up your circuit for Part I. Click here for step-by-step instructions for setting up your circuit for Part 1. Assuming you are starting with no wires connected: 1. Begin by wiring a red wire from the red terminal on the power supply to the right (250mA max) terminal on the ammeter. (Note: if your current goes over 250mA during this experiment, you will need to change ports.) 2. Connect the center (COM) terminal on the ammeter to the right-hand side of the resistor you're using (R1 or R2 on the board), using an alligator clip to attach to the resistor. 3. Using a black wire, connect the left-hand side of the resistor you're using to the black terminal on the power supply (again using an alligator clip). You should now have a loop that goes from your power supply, through your ammeter, through the resistor, and back to the power supply. 4. Connect a red wire from the positive (red) terminal on the voltmeter to the right-hand side of the resistor using a new alligator clip. 5. Connect a black wire from the negative (black) terminal on the voltmeter to the left-hand side of the resistor using another new alligator clip. You should now have made a second loop that runs through your voltmeter instead of through the resistor. This completes the necessary wiring for this part. Once everything is wired up, set your power supply to 5V or so. Measure voltage and current. Slowly turn up your voltage to 10V in units of 1V (again, approximately). Measure voltage and current at each step. Part II: Resistors in Series Wire the circuit up as shown below: Power Supply Voltmeter Click here for step-by-step instructions for setting up your circuit for Part II. Assuming you are starting with no wires connected: 1. 4. Begin by wiring a red wire from the red terminal on the power supply to the right (ZSOmA max) terminal on the ammeter. Connect the center (COM) terminal on the ammeter to the right-hand side of resistor R1, using an alligator clip to attach to the resistor. Using two alligator clips, connect the left-hand side of R1 to the right-hand side of R2. (Note: you may swap r'lel't/right" as long as the resistors are still in serie5.The cartoon figure swaps left/right on R2). Using a black wire, connect the left-hand side of R2 to the black terminal on the power supply. You should now have a loop that goes from your power supply, through your ammeter, through both resistors, and back to the power supply. 4. 5. Connect a red wire from the positive (red) terminal on the voltmeter to the right-hand side of R1 using a new alligator clip. Connect a black wire from the negative (black) terminal on the voltmeter to the left-hand side of R2 using another new alligator clip. You should now have made a second loop that runs through your voltmeter instead of through the resistors. This completes the necessary wiring for this part. Set your voltage to something reasonable (between 5V and 10V) and measure voltage and current. Part III: Resistors in Parallel Wire the circuit up as shown below: Power Sup ply Voltmeter Click here for step-by-step instructions for setting up your circuit for Part III. Assuming you are starting with no wires connected: 1. Begin by wiring a red wire from the red terminal on the power supply to the right (ZSOmA max) terminal on the ammeter. 2. Connect the center (COM) terminal on the ammeter to the right-hand side of resistor R1, using an alligator clip to attach to the resistor. 3. Using a black wire, connect the left-hand side of R1 to the black terminal on the power supply (again using an alligator clip). You should now have a loop that goes from your power supply, through your ammeter, through the resistor R1, and back to the power supply. 4. Connect the right-hand side of resistor R1 to the right-hand side of R2. 5. Use a black wire to connect the left-hand side of R1 to the left-hand side of R2. You should now have a second loop that goes through R2 instead of R1. 6. Connect a red wire from the positive (red) terminal on the voltmeter to the right-hand side of either resistor using a new alligator clip. 7. Connect a black wire from the negative (black) terminal on the voltmeter to the left-hand side of either resistor using another new alligator clip. You should now have made a third loop that runs through your voltmeter instead of through either resistor. This completes the necessary wiring. Set your voltage to something reasonable (between 5V and 10V) and measure voltage and current. Part IV: Light Bulb Wire the circuit up as shown below: Click here for step-bystep instructions for setting up your circuit for Part IV. Assuming you are starting with no wires connected: 1. Begin by wiring a red wire from the red terminal on the power supply to the right (250mA max) terminal on the ammeter. 2. Connect the center (COM) terminal on the ammeter to the right-hand side of the light bulb. 3. Using a black wire, connect the left-hand side of the light bulb to the black terminal on the power supply. You should now have a loop that goes from your power supply, through your ammeter, through the light bulb, and back to the power supply. 4. Connect a red wire from the positive (red) terminal on the voltmeter to the right-hand side of the light bulb using a new alligator clip. 5. Connect a black wire from the negative (black) terminal on the voltmeter to the left-hand side of the light bulb using another new alligator clip. You should now have made a second loop that runs through your voltmeter instead of through the light bulb. This completes the necessary wiring for this part. Set your voltage to something reasonable (say, 5V). Your light bulb should light up. If it does not, consult your TA. Now, turn your voltage down low. Take ten measurements of current and voltage that cover the range between 0-2V. (These voltages produce the best results here, and you want to see the behavior over as much of this range as possible.) 'u'\" '-" "-I- Part1 For the resistor you chose, make a plot of voltage vs. current. Determine the resistance based on this plot. Answer the question on the data sheet about whether your result agreed with expectation. Part II Using the voltage and current you measured, calculate the resistance of the resistors in series. Propagate uncertainty. Using the resistances your TA measured, calculate what the resistance should be. Propagate uncertainty. Answer the question on the data sheet about whether your result agreed with expectation. Part III Using the voltage and current you measured, calculate the resistance of the resistors in parallel. Propagate uncertainty. Using the resistances your TA measured, calculate what the resistance should be. Propagate uncertainty. (The data sheet will help you by breaking this calculation into steps.) Answer the question on the data sheet about whether your result agreed with expectation. Part IV Make a plot of voltage vs. current for the light bulb. Look at the qualitative behavior of this plot, and compare (visually) to Part I. If your data is linear with no intercept (as you should have obseved in part I), then the light bulb acts like an ohmic resistor (voltage is directly proportional to current). If not, then the resistance depends on the current. State your results on your data sheet by answering the stated questions. Back to Tap Copy of DC Circuits Data Sheet File Edit View Insert Format Data Tools Extensions Help $ 5 100% $ % .0 123 Arial 10 + B I A A1 fx K L A B C D E F G H 1 Part I Voltage, V Uncertainty Current, I Uncertainty Part | Plot Slope Intercept W N Unit -.i.. Value Uncertainty 212 (Ignore) (Ignore 10 00 10 You chose to analyze resistor number... 11 Theoretical Values Did your resistance measurement agree with the 12 Quantity R1 R2 Measured R TA's measurement using the multimeter? 13 Unit 14 Value 15 Uncertainty 16 17 Part I Part Ill 18 Quantity Voltage, V Current, I Resistance, R Quantity : Voltage, V Current, I Resistance, R 19 Unit Unit -.;...... 20 Value Value 21 Uncertainty Uncertainty 22 23 Theoretical Values 24 Quantity : R1 R2 Rseries 1/R1 1/R2 1/Rparallel Rparallel 25 Unit 26 Value 27 Uncertainty 28 29 Did your measurement of the resistance of resistors in series agree with your theoretical value? 30 Did your measurement of the resistance of resistors in parallel agree with your theoretical value? 31Part IV Qualitatively, WITat To The Voltage, V Uncertainty Current, I Uncertainty behavior of your data on the V vs. I plot? How does the resistance change as you increase voltage? Is the light bulb Ohmic? Part IV Plot : Slope Intercept Unit Value Uncertainty R^2 (Ignore) (Ignore)Question 1 (5 points) Which of the following are determined in this lab? : Relationship of voltage and current in a resistor Resistance of a resistor : Relationship of voltage and current in a light bulb ' Resistance of a light bulb ' How resistances add (in series) ' How resistances add (in parallel) Question 2 (2 points) When you connect the ammeter in your circuit, you should do it :1: In series with both the resistor(s) and the voltmeter :1: In parallel with the resistor(s), in series with the voltmeter If: In parallel with the voltmeter, in series with the resistor(s) if: In parallel with boththe resistorls) and the voltmeter If: In different ways in different parts of the experiment Question 3 (2 points) When you connect the voltmeter, you should do it a: In series with both the resistor(s) and the ammeter c: In parallel with the ammeter, in series with the resistor(s) if In parallel with the resistor(s), in series with the ammeter II: In parallel with both the resistor(s) and the ammeter :1: In a different manner for different parts of the lab Question 4 (3 points) Based on the theoretical relationship between V and I for an ohmic resistor, should the Vversus I plots you make in this lab have a non-zero intercept? II' Yes (so we do not fit through the origin) a: No (so we can fit through the origin) Question 5 (3 points) Which of the following do we directly measure in this lab? E::l Voltages E::l Currents E::l Resitance (of each resistor)