PHYS140_DC_Circuits_Lab_

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Siena College - General Physics 140 DC Circuits Lab NAME: GROUP MEMBERS: Learning Goals 1. In Section I, you will find a relationship between the current through and potential difference across commercial resistors. Then, you will find the same type of relationship, but for light bulbs, and make comparisons between these two relationships. 2. In Section II, you will identify patterns with respect to what happens to the equivalent resistance of a circuit when resistors are combined in several different ways. 3. In Section III, you will identify patterns as to how the current coming out of the power supply and the potential difference across each resistor changes as you add more identical resistors in series, and then do the same when they are added in parallel. You will then identify patterns for a similar experiment, but when light bulbs are used instead of resistors. Driving Question(s): When too many appliances are on, how does a circuit breaker “know” when to turn off the energy supply? Why might keeping all of the appliances on lead to a fire? Section I - In this part of the lab, you will find a relationship between the current through and potential difference across commercial resistors. Then, you will find the same type of relationship, but for light bulbs, and make comparisons between these two relationships. Equipment: Power supply, multimeter, various commercial resistors, lightbulbs, connecting wires. Scientific Ability Missing Inadequate Needs Improvement Adequate B2 Is able to design a reliable experiment that investigates the phenomenon The experiment does not investigate the phenomenon. The experiment may not yield any interesting patterns. Some important aspects of the phenomenon will not be observable. The experiment might yield interesting patterns relevant to the investigation of the phenomenon. B3 Is able to decide what parameters are to be measured and identify independent and dependent variables The parameters are irrelevant. Only some of the parameters are relevant. The parameters are relevant. However, independent and dependent variables are not identified. The parameters are relevant and independent and dependent variables are identified. G4 Is able to record and represent data in a meaningful way The data is either absent or incomprehensible. Some important data is absent or incomprehensible. The data is not All important data is present, but it is recorded in a way that requires some All important data is present, organized, and recorded clearly. The tables 1

Siena College - General Physics 140 DC Circuits Lab organized in tables or the tables are not properly labeled. effort to comprehend. The tables are labeled, but the labels are confusing. are labeled and placed in a logical order. A11 Graph No graph is present. A graph is present, but the axes are not labeled. There is no scale on the axes. The data points are incorrectly connected to each other instead of using an appropriate trendline. The graph is present and the axes are labeled, but the axes do not correspond to the independent and dependent variable OR the scale is not accurate. The data points are not connected to each other, but there is no trendline either. The graph has correctly labeled axes, the independent variable is along the horizontal axis and the scale is accurate. The trendline is correct. B7 Is able to identify a pattern in the data No attempt is made to search for a pattern. The pattern described is irrelevant or inconsistent with the data. The pattern has minor errors or omissions. The pattern represents the relevant trend in the data. SAFETY NOTE: Be careful to NOT supply too large of a current to either the resistor or the light bulb. A safe range of current is less than 0.08 A for the resistor and less than 0.30 A for the bulb. While experimenting, always make sure the resistor is never starting to smoke and the lightbulb is not overly bright. Use a variable power supply to vary the potential difference across and measure the current through a “mystery” resistor, and then do the same for a lightbulb. Do NOT measure the resistance of the resistor or light bulb by using the multimeter in Section I. Also, do NOT rely on the current measurement that is being displayed on the power supply. Use a multimeter to measure the current instead. COLAB LINK: https://colab.research.google.com/drive/1t67uC- 4VpRZyQOL6XTBkVi3DODmGMq2C?usp=sharing A. Describe the procedure for your investigation and describe the experimental setup. Include labeled circuit diagrams. You should have 2 circuit diagrams in total. Procedure Steps for a Mystery resistor 1) Connect a black wire and red wire to the power supply 2) Then get a mystery resistor and connect the black wire to the black wire from the current reader 3) Connect the red wire to the resistor and then connect a yellow wire to the end of the resistor. 2

Siena College - General Physics 140 DC Circuits Lab 4) Then connect the other end of the yellow wire to the red wire from the current reader. 5) Start off the voltage at 3V and collect the current data from the reader 6) Repeat this step 4 more times while increasing the voltage in increments of .5 and do not exceed 6 Procedure Steps for lightbulb 1) Connect a black wire and red wire to the power supply 2) Then get a mystery resistor and connect the black wire to the black wire from the current reader 3) Connect the red wire to a side that the bulb is one and connect one end of the yellow wire to the other end of the bulb 4) Then connect the other end of the yellow wire to the red wire from the current reader. Start off the voltage at 3V and collect the current data from the reader 5) Repeat this step 4 more times while increasing the voltage in increments of .5 and do not exceed 6 B. What important physical quantities change during your experiment? What are the independent and dependent variables? 3

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Siena College - General Physics 140 DC Circuits Lab The independent variable is the voltage and the dependent variable is the current (I). As the voltage increases so does the current. C. Record your data in 2 separate data tables - one for the resistor and one for the light bulb. Do NOT rely on the current measurement that is being displayed on the power supply. Use a multimeter to measure the current instead. Then, calculate the ratio of the potential difference across the resistor (and light bulb) and the current through it for every potential difference reading . Include this calculated result as a separate column in your data tables. Resistor Volts (V) Current (mA) 3.5 0.02 4.0 0.03 4.5 0.04 5.1 0.05 6.0 0.06 Lightbulb Volts (V) Current (A) 2.1 0.14 2.6 0.16 3.0 0.172 3.4 0.185 4.0 0.20 4.4 0.21 5.1 0.23 6.0 0.25 4

Siena College - General Physics 140 DC Circuits Lab 6.4 0.262 D. Use your data tables to construct a potential difference (y) versus current (x) graph for the resistor and light bulb. Try to include both sets of data on the same graph so that you can easily make comparisons between the data for the resistor and light bulb. Include an appropriate trendline for each set of data. What physical quantity does the slope represent? 5

Siena College - General Physics 140 DC Circuits Lab The slope represents the resistance in the circuit. For the resistor the resistance is linear so that means the resistance is constant. As for the lightbulb the resistance is non-linear so that means it’s not constant. E. The ratio of potential difference across the resistor (or light bulb) and the current through it for each potential difference is called resistance . When rearranged, (I = ΔV/R eq ), this ratio is also known as Ohm’s Law. What patterns do you notice with respect to what is happening to the value of the resistance of the resistor and light bulb for different potential differences across each? As resistance and voltage increases so does the current. F. Use the multimeter to measure the resistance of the resistor (and then the light bulb) that is not connected to the power supply. Does it match your findings in part C? Yes Section II - In this part of the lab, you will identify patterns with respect to what happens to the equivalent resistance of a circuit when resistors are combined in several different ways. 6

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Siena College - General Physics 140 DC Circuits Lab Equipment: Multimeter, various commercial resistors, connecting wires. Scientific Ability Missing Inadequate Needs Improvement Adequate B8 Is able to represent a pattern mathematically (if applicable) No attempt is made to represent a pattern mathematically. The mathematical expression does not represent the trend. The mathematical expression represents the trend. However, an analysis of how well the expression agrees with the data is not included, or some features of the pattern are missing. The mathematical expression represents the trend completely and an analysis of how well it agrees with the data is included. C7 Is able to decide whether the prediction and the outcome agree or disagree No mention of whether the prediction and outcome agree or disagree. A decision about the agreement or disagreement is made, but is not consistent with the outcome of the experiment. A reasonable decision about the agreement or disagreement is made, but experimental uncertainty is not taken into account. A reasonable decision about the agreement or disagreement is made and experimental uncertainty is taken into account. You have been supplied with three resistors. Set the multimeter as an ohmmeter, and measure the resistance of each of the resistors. Record the resistance of each below: R 1 = 110 R 2 = 240 R 3 = 620 A. Now, connect the resistors as shown in each diagram below, determine the equivalent resistance by measurement, and record the results. Do NOT calculate anything yet! Circuit MEASURED Equivalent Resistance, R eq (Ohms, Ω) CALCULATED Equivalent Resistance, R eq (Ohms, Ω) 718 730 344 340 Now that you have measured the equivalent resistance of circuits 1 and 2, use your results to come up with a mathematical relationship that quantifies the equivalent resistance of resistors that are wired in SERIES . Show the 7

Siena College - General Physics 140 DC Circuits Lab mathematical relationship below, and then use this relationship to calculate the equivalent resistance for each circuit in the table above. How well does your calculated value agree with your measured value? RT = R1 + R2 + R3. B. Now, connect the resistors as shown in each diagram below, determine the equivalent resistance by measurement, and record the results. Do NOT calculate anything yet! Circuit MEASURED Equivalent Resistance, R eq (Ohms, Ω) CALCULATED Equivalent Resistance, R eq (Ohms, Ω) 74.7 75.4 92.6 93.4 Now that you have measured the equivalent resistance of circuits 3 and 4, use your results to come up with a mathematical relationship that quantifies the equivalent resistance of resistors that are wired in PARALLEL . Show the mathematical relationship below, and then use this relationship to calculate the equivalent resistance for each circuit in the table above. How well does your calculated value agree with your measured value? 1/Rt = 1/R1 + 1/R2 + 1/R3 +... C. In the table below, first predict the equivalent resistance of each circuit by using the mathematical relationships you developed in parts (A) and (B). Then, measure each equivalent resistance using the multimeter. Circuit PREDICTION: Calculated Equivalent Resistance, R eq (Ohms, Ω) MEASURED Equivalent Resistance, R eq (Ohms, Ω) 8

Siena College - General Physics 140 DC Circuits Lab 223.7 220 694.7 329 Make a statement about how well your prediction (the calculated value) agrees with your outcome (the measured value) while also taking into account experimental uncertainty. The prediction agrees with the outcome because they’re only slight differences in the the calculated value. Section III - In this part of the lab, you will identify patterns as to how the current coming out of the power supply and the potential difference across each resistor changes as you add more identical resistors in series, and then do the same when they are added in parallel. You will then identify patterns for a similar experiment, but when light bulbs are used instead of resistors. Equipment: Power supply, multimeter, various commercial resistors, lightbulbs, connecting wires. Scientific Ability Missing Inadequate Needs Improvement Adequate B2 Is able to design a reliable experiment that investigates the phenomenon The experiment does not investigate the phenomenon. The experiment may not yield any interesting patterns. Some important aspects of the phenomenon will not be observable. The experiment might yield interesting patterns relevant to the investigation of the phenomenon. B3 Is able to decide what parameters are to be measured and identify independent and dependent variables The parameters are irrelevant. Only some of the parameters are relevant. The parameters are relevant. However, independent and dependent variables are not identified. The parameters are relevant and independent and dependent variables are identified. G4 Is able to record and represent data in a meaningful way The data is either absent or incomprehensible. Some important data is absent or incomprehensible. The data is not All important data is present, but it is recorded in a way that requires some All important data is present, organized, and recorded clearly. The tables are 9

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Siena College - General Physics 140 DC Circuits Lab organized in tables or the tables are not properly labeled. effort to comprehend. The tables are labeled, but the labels are confusing. labeled and placed in a logical order. B7 Is able to identify a pattern in the data No attempt is made to search for a pattern. The pattern described is irrelevant or inconsistent with the data. The pattern has minor errors or omissions. The pattern represents the relevant trend in the data. SAFETY NOTE: Be careful to NOT supply too large of a potential difference to either the resistor(s) or the light bulb(s). A safe range of potential difference will depend on the resistance of the resistor(s) and bulb(s) you are using, so please consult with your instructor first. While experimenting, always make sure the resistor is never starting to smoke and the light bulb is not overly bright. Obtain 2 identical resistors and 2 identical light bulbs. Use a power supply to always maintain a constant potential difference across each arrangement of identical resistors, and then do the same with using light bulbs. You may use your data from Section I for a single resistor so that you can move right into having 2 resistors in series. Then do the same but with arranging the resistors in parallel. Last, repeat the same experiments by using light bulbs instead of resistors. For a constant value of potential difference for every circuit arrangement, you will need to measure (1) the current coming out of the power supply, (2) the current through EACH resistor (or light bulb), and (3) the potential difference across each resistor (or light bulb). A. Describe the procedure for your investigation and describe the experimental setup. Include labeled circuit diagrams. You should have 4 circuit diagrams in total. You do not need to include circuit diagrams for only 1 light bulb or 1 resistor as you already did this in Section I. Procedure Steps for a Mystery resistor 1) Connect a black wire and red wire to the power supply 2) Connect another black wire to the current reader and connect that wire to the other black wire from the power supply 3) Get 2 yellow wires and connect that to the red wire from the current reader 4) Connect 2 yellow wires to the red wire from the power supply 5) Take one of the yellow wires to a resistor and connect it to the yellow wire from the current reader. 6) Take the other yellow wire from the power supply and connect the other end to a resistor and connect that to the other yellow wire that’s connected to the current reader 10

Siena College - General Physics 140 DC Circuits Lab B. What important physical quantities change during your experiment? What are the independent and dependent variables? There may be more than one dependent variable. The independent variable is the volts and the dependent variable is the current. C. Use the mathematical relationships that you used in your investigations in Section I (Ohm’s Law) and Section II (equivalent resistance) to make predictions for the current coming out of the power supply for each circuit arrangement. Show all of your calculations. D. Record your data in 4 separate data tables - one for the resistors in series, one for the resistors in parallel, one for the light bulbs in series, and one for the light bulbs in parallel. V(ps) I of resistor V across each resistor Resistors in series 1. 110 3.7 0.34 2.6 2. 620 3.7 0.06 2.9 Resistors in Parallel 1. 110 3.7 .034 3.78 2. 110 3.7 .034 3.78 E. What patterns do you notice with respect to what is happening to the current coming out of the power supply as you add more resistors (or light bulbs) in SERIES versus PARALLEL? Based on these results, what might be the role of a circuit breaker in maintaining a safe circuit? F. What patterns do you notice with respect to what is happening to the current through each resistor (or light bulb) as you add more of them in SERIES versus PARALLEL? G. What patterns do you notice with respect to what is happening to the potential difference across each resistor (or light bulb) as you add more of them in SERIES versus PARALLEL? 11

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