HANDS-ON ACTIVITY 4 BUILDING SERIES AND PARALLEL CIRCUITS BACKGROUND WIRING DIRECTIONS

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1 ACTIVITY 4 BUILDING SERIES AND PARALLEL CIRCUITS BACKGROUND Make sure you read the background in Activity 3 before doing this activity. WIRING DIRECTIONS Materials per group of two: one or two D-cells and holders, three lightbulbs and holders, six pieces of insulated wire with stripped ends (or six wires with alligator clips on each end) 1. Below are diagrams showing three bulbs in series and in parallel. Build these same circuits using one or two 1.5-volt D-cells (flashlight-type), three bulbs, some wire with stripped ends, and alligator clips to help hold wires together. Connecting wires through holes in a circuit board will help you keep your wiring in a rectangular pattern. (Christmas tree lights make good sources for lightbulbs.) 2. Record how the brightnesses of the bulbs in the series and parallel circuits change as you increase the bulbs in the circuits from one to two to three. SERIES CIRCUIT PARALLEL CIRCUIT Note: Your homemade circuits, especially the parallel circuits, will look quite a bit different from the neat rectangular diagrams shown above (rectangles will look more like circles). Activity 4 - Page 1/3

2 ACTIVITY 4 BUILDING SERIES AND PARALLEL CIRCUITS QUESTIONS SERIES CIRCUIT PARALLEL CIRCUIT 1. Which bulbs are brighter? a. The three bulbs wired in series. b. The three bulbs wired in parallel. c. They're the same. 2. What happens to the brightness as you add bulbs in series? a. The bulbs get brighter. b. The bulbs get dimmer. c. The bulbs stay the same. 3. What happens to the brightness as you add bulbs in parallel? a. The bulbs get brighter. b. The bulbs get dimmer. c. The bulbs stay the same. 4. What do you think these lighting differences suggest about the voltage across the bulbs in series circuits? a. The voltage across each bulb is less each time a similar bulb is added. b. The voltage across each bulb is more each time a similar bulb is added. c. The voltage across each bulb stays the same each time a similar bulb is added. 5. What do you think these lighting differences suggest about the voltage across the bulbs in parallel circuits? a. The voltage across each bulb is less each time a similar bulb is added. b. The voltage across each bulb is more each time a similar bulb is added. c. The voltage across each bulb stays the same each time a similar bulb is added. Activity 4 - Page 2/3

3 ACTIVITY 4 BUILDING SERIES AND PARALLEL CIRCUITS QUESTIONS (CONTINUED) DRY CELLS WIRED IN SERIES DRY CELLS WIRED IN PARALLEL 6. What happens to the brightness of the three bulbs wired in series as you add a dry cell in series? a. The bulbs get brighter. b. The bulbs get dimmer. c. The bulbs stay the same. 7. What happens to the brightness of the three bulbs wired in series as you add a dry cell in parallel with the first one? a. The bulbs get brighter. b. The bulbs get dimmer. c. The bulbs stay the same. 8. What happens to the brightness of the three bulbs wired in parallel as you add a dry cell in series with the first one? a. The bulbs get brighter. b. The bulbs get dimmer. c. The bulbs stay the same. 9. What happens to the brightness of the three bulbs wired in parallel as you add a dry cell in parallel with the first one? a. The bulbs get brighter. b. The bulbs get dimmer. c. The bulbs stay the same. Activity 4 - Page 3/3

4 ACTIVITY 8 A FANCY SWITCH BACKGROUND In this activity you'll have a chance to wire the fancy switch used to turn on a hallway light from either end of the corridor. The two switches are actually wired to each other as well as to the light and power source. These switches are called three-way or single-pole, double-throw (SPDT) switches. Parallel circuits have multiple paths for the flow of electricity. This switch takes advantage of both series and parallel wiring. A single-pole, double-throw switch is the kind of switch (for example, a light switch) found at each entrance of rooms with two entrances. The switches are wired both to the light and to each other on each side of the hallway. That makes a different circuit for each position of the first switch. One position of the second switch is also included in the circuit. Depending on the position of both switches, throwing one switch opens or closes the circuit to the other switch as well as the one to the light. This way, when the other switch is thrown, it will perform the desired function. Wiring diagram of a three-way or singlepole, double-throw switch. WIRING CHALLENGE Materials: D-cell "battery" and holder, a lightbulb and holder, two index cards, two paper clips, six metal brads, six brass washers, insulated wire, and a shoebox or shoebox lid This is what an index card SPDT switch might look like. Activity 8 - Page 1/3

5 ACTIVITY 8 A FANCY SWITCH WIRING CHALLENGE (CONTINUED) PREDICTIONS For the diagram below, predict whether the light will be on or off when the switches are in the following positions: 1. Switch 1 is in position A, and switch 2 is in position C. a. On b. Off 2. Switch 1 is in position B, and switch 2 is in position D. a. On b. Off 3. Switch 1 is in position A, and switch 2 is in position D. a. On b. Off 4. Switch 1 is in position B, and switch 2 is in position C. a. On b. Off This is what your wired shoebox room might look like. 1. Build two switches, one for each end of the room, using three metal brads inserted into an index card. The middle brad should be inserted through the end of a paper clip. Washers secure the brads on the back side of the index card. The other two brads should be exactly the length of the paper clip away. When the paper clip swings in both directions, it should be able to make solid contact with the other two brads. Activity 8 - Page 2/3

6 ACTIVITY 8 A FANCY SWITCH WIRING CHALLENGE CONTINUED 2. Wire a "shoebox room" with one switch on each end. Use either a shoebox or shoebox lid as the frame of your room. Wired Shoebox Room QUESTIONS 1. Try the switch in all of the above positions. When is the light actually on and off? a. Switch 1 is in position A, and switch 2 is in position C. a. On b. Off b. Switch 1 is in position B, and switch 2 is in position D. a. On b. Off c. Switch 1 is in position A, and switch 2 is in position D. a. On b. Off d. Switch 1 is in position B, and switch 2 is in position C. a. On b. Off 2. Predict what would happen if a piece of uninsulated wire were to fall between Switch 1 points A and B, touching both metal contact points. a. Switch 1 is in position A, and switch 2 is in position C. a. On b. Off b. Switch 1 is in position B, and switch 2 is in position D. a. On b. Off c. Switch 1 is in position A, and switch 2 is in position D. a. On b. Off d. Switch 1 is in position B, and switch 2 is in position C. a. On b. Off 3. With the loose wire still connecting points A and B, what would happen if the lower "paper clip switch" was left in the middle position shown, touching neither point C nor point D? a. Always On b. Always Off Activity 8 - Page 3/3

7 ACTIVITY 9 USING METERS BACKGROUND Voltmeters are connected across the device whose voltage you wish to determine. The red wire is connected to the positive end of the voltmeter and the positive side of the power source (battery, solar cell, etc.) or other device (lightbulb, resistor, motor, buzzer, etc.). The black wire is connected to the negative end of the voltmeter and the negative side of the power source or other device. Basically, you are wiring the voltmeter in parallel with, or across, the device. Voltage is measured with a closed circuit so that current is flowing through the device. Note: Meters are represented by a circle containing the letter abbreviation for the unit being measured (V, A, or Ω). VOLTMETER WIRED IN PARALLEL TO A D-CELL IN A CLOSED CIRCUIT. VOLTMETER WIRED IN PARALLEL TO A RESISTOR IN A CLOSED CIRCUIT. Ammeters are connected in series with the circuit whose current you wish to determine. (Remember that the same current runs through all devices in a series circuit.) The red wire from the ammeter is usually connected to the positive terminal of the power source (battery, solar cell, etc.). The black wire is usually connected to the negative terminal of the power source. Current is measured with a closed circuit so that current from the battery is flowing through the circuit. AMMETER WIRED IN SERIES TO A D-CELL AND A RESISTOR IN A CLOSED CIRCUIT. Activity 9 - Page 1/11

8 ACTIVITY 9 USING METERS (CONTINUED) OHMMETERS are connected across the device whose resistance you wish to determine - with the device DISCONNECTED from its power source (battery). Touch the two meter probes together before measuring the desired object's resistance to zero the meter. The red wire of the ohmmeter is connected to one end of the load (the negative side), and the black wire is connected to the other (positive) side of the load (lightbulb, resistor, etc.). Basically, you are wiring the ohmmeter in series with the load. Resistance is measured with an OPEN circuit so that NO current is flowing through the device except that coming from the ohmmeter. DO NOT measure the resistance of batteries. OHMMETER WIRED IN SERIES TO A RESISTOR IN AN OPEN CIRCUIT. MULTIMETERS measure all three values (voltage, resistance, and current). METER SETTINGS Most meters have a range of measurement values (for example, 0-1, 1-10, ) that you need to preset by turning a dial. Most of the time we will be working with low quantities of voltage, current, and resistance (1-6 volts, milliamps, ohms). Choose the meter setting closest to BUT GREATER THAN the value you expect to be working with. Choosing a lower setting can damage the meter. Note that the current scale is given in milliamps (ma). The prefix milli in front of a unit means 1/1,000. Thus, 1 ma = A. For Ohm's law calculations, you will need to convert your milliamp readings back to amps. This is the same as dividing milliamps by 1,000, or sliding the decimal three positions to the left. For example, 28.5 ma = A. For the ohmmeter used to measure resistance, you may see X1K or X10. This means that the meter reading needs to be multiplied by 1,000 (for X1K) or 10 (for X10). A mirrored backing within the measurement scales of analog multimeters is used to line up the needle with its reflection to obtain the most accurate reading. Digital meters display their results as numbers. Activity 9 - Page 2/11

9 ACTIVITY 9 USING METERS METER SETTINGS CONTINUED The numbers you'll be working with are small (no more than 6 volts DC, no more than 250 milliamps of current, and no more than 500 ohms of resistance) so that they will work with the DC dry cells and other parts you'll use for the hands-on activities. ANALOG MULTIMETER DIGITAL MULTIMETER DECODING COLORED RESISTOR BANDS Resistors are marked with four bands that indicate their resistance in ohms (Ω). The first band is on one of the bulging ends of the resistor. The first band's number is the first number of the resistance value. The second band's number is the second number of the resistance value. The third band represents the number of zeros following the first two numbers. People often forget that a third band zero value means the resistor has only TWO numbers with no zeros. The fourth band indicates the percentage accuracy of the coded value. Gold means ± 5 percent. Silver means ± 10 percent. Thus a resistor with the band colors brown, black, brown, and gold has a resistance value of 100 Ω and a range of 95 to 105 Ω. If the final band would have been silver, its range of expected resistance would be 90 to 110 Ω. A resistor with four color bands. Can you decipher the band code? Try it! Compare your result to the answer at the end of this activity. Resistor values can be decoded using the table below for the first three bands. Remember that the third band represents the number of zeros after the first two numbers. Activity 9 - Page 3/11

10 ACTIVITY 9 USING METERS DECODING COLORED RESISTOR BANDS (CONTINUED) TABLE OF RESISTOR COLOR BAND CODES Color Value Color Value Black 0 Green 5 Brown 1 Blue 6 Red 2 Violet 7 Orange 3 Gray 8 Yellow 4 White 9 IMPORTANT METER RULES a. Power: Turn OFF meters and disconnect circuits between readings, while changing meter settings, and after taking the last measurement. b. Resistance: Disconnect a device from the circuit before measuring its resistance. Once the meter is set to 200-2,000 ohms (Ω), turn on the meter and touch the two probes together to zero the meter before taking the resistance measurement. Do NOT measure the resistance of batteries or devices connected in closed circuits. c. Current: Measure current by opening the circuit to include the ammeter probes in series. Do NOT measure current by connecting probes to both battery terminals. d. Connections: Refer to the first four background diagrams to see how to correctly connect the meter for each measurement. IMPORTANT MEASUREMENT QUESTIONS Before making each measurement, ask yourself these three questions: 1. What am I going to measure (voltage, current, or resistance)? 2. Is the meter hooked up correctly for that measurement? 3. Is the meter set to the correct unit for that measurement? PART 1 METER POSTERS To protect the meters, this activity should be done before making the actual measurements. Materials (per team of two to four students): This handout, pencils, several different colored markers, insulated copper wire, one battery holder BUT NO BATTERY, one multimeter, one 100-Ω resistor Activity 9 - Page 4/11

11 ACTIVITY 9 USING METERS PART 1 METER POSTERS (CONTINUED) Make three posters that include the title and four drawings (two pairs of DO and two pairs of DON'T circuit and meter face diagrams) for each measurement as follows: VOLTAGE (VOLTS, V) POSTER 1. "DO" CIRCUIT DIAGRAM: How to connect the multimeter into the circuit to measure voltage. 2. "DON'T" CIRCUIT DIAGRAM: How NOT to connect the multimeter into the circuit to measure voltage (should be Xd out). 3. "DO" METER FACE: How to set the multimeter for the level of voltage it will be measuring. 4. "DON'T" METER FACE: How NOT TO set the multimeter for the level of voltage it will be measuring (should be Xd out). CURRENT (AMPS, A; OR MILLIAMPS, MA) POSTER 1. "DO" CIRCUIT DIAGRAM: How to connect the multimeter into the circuit to measure current. 2. "DON'T" CIRCUIT DIAGRAM: How NOT to connect the multimeter into the circuit to measure current (should be Xd out). 3. "DO" METER FACE: How to set the multimeter for the level of current it will be measuring. 4. "DON'T" METER FACE: How NOT to set the multimeter for the level of current it will be measuring (should be Xd out). RESISTANCE (OHMS, Ω) POSTER 1. "DO" CIRCUIT DIAGRAM: How to connect the multimeter into the OPEN circuit to measure resistance (or just measure the resistor separately). 2. "DON'T" CIRCUIT DIAGRAM: How NOT to connect the multimeter into the circuit to measure resistance (should be Xd out). 3. "DO" METER FACE: How to set the multimeter for the level of resistance it will be measuring. 4. "DON'T" METER FACE: How NOT to set the multimeter for the level of resistance it will be measuring (should be Xd out). Activity 9 - Page 5/11

12 ACTIVITY 9 USING METERS PART 1 METER POSTERS (CONTINUED) Here is a sample Voltage poster. Many other diagrams would also work. Blank Dos and Don'ts sheets are attached at the end of this activity. VOLTAGE MEASUREMENTS (IN VOLTS, V) DO DON'T DO DON'T Activity 9 - Page 6/11

13 ACTIVITY 9 USING METERS (CONTINUED) PART 2 WIRING AND MEASUREMENT DIRECTIONS You may find it helpful to review the Ohm's law formulas in the first computer activity before you begin. Materials per team of two students: four pieces of insulated copper wire, one 1.5-volt D cell, one battery holder, one multimeter, one 100-Ω resistor, four alligator clips 1. Make a circuit connecting one resistor (between 10 and 500 Ω) and one 1.5-V dry cell in series. The circuit should be closed. Simple circuit with one dry cell and one resistor. Dial to the appropriate DC V (direct current voltage) setting (for example, 9 V). Attach the multimeter across the D-cell, making sure to attach the positive ends and the negative ends to the correct sides as indicated on the meter and cell. By convention we use the red wire to connect positive sides and the black wire to connect negative sides of devices like the voltmeter that are wired in parallel. Record this and all future meter readings to three significant figures. See the first background voltmeter graphic to connect the meter. Voltage across battery volts 2. Repeat the voltage measurement across the resistor. Enter the voltage reading below. See the second voltmeter graphic to connect the meter. Voltage across resistor volts 3. Is the voltage the same across the dry cell as it is across the resistor? Activity 9 - Page 7/11

14 ACTIVITY 9 USING METERS PART 2 WIRING AND MEASUREMENT DIRECTIONS (CONTINUED) 4. For current you will need to break your circuit. First, change the dial setting to the most appropriate DC amps (A) scale. Look for a setting around 200 ma. Pick the most convenient location for breaking the circuit and reclosing it by attaching the red and black leads from the meter in series. Enter the circuit current in amps, which will require a conversion from ma (slide the decimal three places to the left, which is the same as dividing by 1,000, to convert from ma to A). Note: See the background ammeter graphic to connect the meter. If the meter reading has a negative value, drop the negative sign when you record the value. Current through circuit milliamps amps 5. Is the current the same no matter where you insert the ammeter into the circuit? 6. Finally, to measure the resistance of the resistor, adjust the meter to the lowest setting (between 200 and 2,000 Ω) that is higher than your expected resistance (based on decoding the colored resistor bands). The circuit should be left open for this resistance measurement, or you can totally disconnect the resistor. The meter's battery supplies the necessary electric current. See the background ohmmeter graphic. Note: Keep in mind that resistors are accurate to ± 5 percent if ending in a gold band and ± 10 percent if ending in a silver band. This means that a 100-Ω resistor reading would be expected to be anywhere between 95 and 105 ohms for the gold band, or 90 to 110 ohms for the silver band. Measured resistance of resistor ohms 7. Using the battery voltage and the current you measured in numbers 1 and 4 above, use Ohm's law to calculate the expected resistance. ohms SUMMARY QUESTION 8. Does R = V / I? (Is your calculated resistance within 5 percent of measured resistance?) In other words, did you confirm Ohm's law? ANSWER TO BAND CODE QUESTION 47 ± 2.35 ohms (Did you remember that the third band stands for the number of zeros following the first two numbers?) Activity 9 - Page 8/11

15 ACTIVITY 9 USING METERS VOLTAGE MEASUREMENTS (IN VOLTS, V) DO DON'T DO DONT Activity 9 - Page 9/11

16 ACTIVITY 9 USING METERS CURRENT MEASUREMENTS (IN MILLIAMPS, ma) DO DON'T DO DON'T Activity 9 - Page 10/11

17 ACTIVITY 9 USING METERS RESISTANCE MEASUREMENTS (IN OHMS, Ω) DO DON'T DO DON'T Activity 9 - Page 11/11

18 ACTIVITY 10 ADVANCED METER MEASUREMENTS In this activity you'll have a chance to use meters to test Kirchhoff's laws for series and parallel circuits. Make sure you have done the previous activity, Using Meters, first so that you are completely familiar with how to make each measurement, including when to connect the meter in series, when to connect it in parallel across the device to be measured, and when to measure with an open circuit. BACKGROUND You may find it helpful to review the Series Circuit Calculations, Parallel Circuit Calculations, and Using Meters activities before you begin so that you are completely familiar with how to make each measurement (when to connect the meter in series, when to connect it in parallel across the device to be measured, and when to measure with an open (disconnected) circuit). IMPORTANT: To avoid damaging the multimeter, review the meter rules in the previous activity. REMINDERS - SERIES CIRCUITS a. Total voltage is equal to the sum of the individual voltages. b. Current is the same anywhere it is measured through the same circuit path. c. Total resistance is equal to the sum of the individual resistances of the circuit loads. REMINDERS - PARALLEL CIRCUITS a. Total voltage is the same as the voltage of the source dry cell across each circuit path. b. Current is equal to the sum of the individual currents. The sum of the currents entering a circuit junction (intersection point) equals the sum of the currents leaving a circuit junction. c. Resistance follows the reciprocal formula below. 1 R Total = R 1 R 2 R 3 d. Ohm's law remains V = I R, or V T = I T R T, and V 1 = I 1 R 1 for circuit branch 1, V 2 = I 2 R 2 for branch 2, etc. Activity 10 - Page 1/6

19 ACTIVITY 10 ADVANCED METER MEASUREMENTS (CONTINUED) PART 1 WIRING AND MEASURING VOLTAGE, CURRENT, AND RESISTANCE IN A SERIES CIRCUIT Materials: four insulated copper wires, one multimeter, two 1.5-volt D cells, two dry cell holders, one 100-Ω resistor, one 220-Ω resistor, four alligator clips 1. Make a circuit connecting two resistors and two 1.5-V dry cells in series. The circuit should be closed. Note: To wire dry cells in series, connect the positive end of one to the negative end of the other. Your series circuit should like something like this, with more looped than rectangular wires. 2. Dial to the lowest DC V (direct current voltage) setting (but not lower than the voltage of your circuit). Attach the multimeter across the dry cell to measure the voltage, making sure to connect the positive end and the negative end of the meter to the like sides on the dry cell and circuit. By convention, we use the red wire to connect positive sides and the black wire to connect negative sides of devices. Enter your results in the table below. Measure the dry cell on the left first. Then continue voltage measurements in a counterclockwise direction. Reading Measurement Voltage (V) SERIES CIRCUIT DATA TABLE Current (A) Activity 10 - Page 2/6 Calculated Resistance (Ω) Measured Resistance (Ω) 1 Dry Cell 1 Should be zero Do not measure 2 Dry Cell 2 Should be zero Do not measure Ω Resistor Ω Resistor R Total : 3. Repeat the voltage measurement across the second dry cell. Enter the voltage.

20 ACTIVITY 10 ADVANCED METER MEASUREMENTS WIRING AND MEASURING VOLTAGE, CURRENT, AND RESISTANCE IN A SERIES CIRCUIT (CONTINUED) 4. Take the voltage measurement across each of the resistors, starting with the one on the right. Record the resistor voltages in the table. 5. For current, break the circuit to insert the ammeter as pictured. Close the circuit by attaching the red and black leads from the meter (red meter lead toward the positive dry cell terminal, black toward the negative dry cell terminal). Change the multimeter setting to the most appropriate DC amps (A) scale. Remember, the current through the most common small resistors is around 0.2 A (200 ma). Enter the current in amps, which may require a conversion from ma (slide the decimal three places to the left to convert from ma to A). Insert the meter into the circuit as shown below for readings 1 through 4. Reconnect the meter in series for each of the positions shown in the diagram below to obtain the remaining current measurements. Diagram showing locations to insert the ammeter into the series circuit to take current readings 1 through 4. The ammeter is represented by an A with a circle around it. 6. Use the appropriate version of Ohm's law to calculate the total resistance of the circuit. Enter your answer after R Total : in the data table. 7. Turn the meter off. Change the multimeter setting to the most appropriate ohms (Ω) scale (less than 500 ohms for small resistors). Either REMOVE THE RESISTORS FROM THE CIRCUIT or DISCONNECT A WIRE so that the circuit is OPEN for the resistance measurements. Turn on the meter and zero it by touching the two probes together before each measurement. Measure resistance across each of the two resistors. Record the answers in the table above. Activity 10 - Page 3/6

21 ACTIVITY 10 ADVANCED METER MEASUREMENTS SERIES CIRCUIT MEASUREMENT QUESTIONS DO THE MATH 1. Does V = I R (to within 5 percent measurement error)? Compare measured and calculated values across each load (the resistors) to be sure. a. Yes b. No 2. Does total voltage (the voltage of the sum of the dry cells) equal the sum of the voltages across each resistor? a. Yes b. No 3. Are currents equal anywhere you try to measure them in your series circuit? a. Yes b. No 4. Does total resistance calculated from R T = V T / I T equal the sum of the measured resistances across each load? a. Yes b. No PART 2 WIRING AND MEASURING VOLTAGE, CURRENT, AND RESISTANCE IN A PARALLEL CIRCUIT Materials: four insulated copper wires, one multimeter, two 1.5-volt D cells, two dry cell holders, one 100-Ω resistor, one 220-Ω resistor, four alligator clips 1. Build a parallel circuit using two dry cells and two resistors, wiring the two dry cells in parallel and wiring the two resistors in parallel. Connect the 220-ohm resistor on the far right. Note: To wire dry cells in parallel, connect the positive ends to each other, then connect the negative ends to each other. Your parallel circuit should look something like this, with more looped than rectangular wires. 2. Dial to the lowest DC V (direct current voltage) setting. Measure the dry cell on the left first. Attach the multimeter across the dry cell to measure the voltage, making sure to connect the red and black leads of the meter to the positive and negative terminals on the dry cell, respectively. Enter your results in the Parallel Circuit Data Table. Activity 10 - Page 4/6

22 ACTIVITY 10 ADVANCED METER MEASUREMENTS PART 2 WIRING AND MEASURING VOLTAGE, CURRENT, AND RESISTANCE IN A PARALLEL CIRCUIT (CONTINUED) PARALLEL CIRCUIT DATA TABLE Reading Measurement Voltage (V) Current (A) Calculated Resistance (Ω) Measured Resistance (Ω) 1 Dry Cell 1 Should be zero Do not measure 2 Dry Cell 2 Should be zero Do not measure Ω Resistor R 1 : Ω Resistor R 2 : 3. Repeat the voltage measurement across the second dry cell. Record the voltage. 4. Repeat the voltage measurement across each of the resistors, starting with the one on the left. Enter the resistor voltages. 5. For current break the circuit as pictured for reading 1 and close it by connecting the red and black leads from the meter. Change the multimeter setting to the most appropriate DC amps (A) scale (200 ma). Enter the current in amps, which requires a conversion from ma (slide the decimal three places to the left to convert from ma to A). Insert the meter into the circuit as shown below for readings 2 through 4. Record your current values. Diagram showing locations to insert the ammeter into the parallel circuit to take current readings 1 through Use the appropriate version of Ohm's law to calculate the two resistor resistances (R 1 and R 2 ). Calculate the resistance of the first resistor (R 1 ) using the Dry Cell 2 voltage and the reading 2 current (reading 1 is the total current). Calculate the resistance of the second resistor (R 2 ) using the Dry Cell 2 voltage and the reading 4 current. Activity 10 - Page 5/6

23 ACTIVITY 10 ADVANCED METER MEASUREMENTS (CONTINUED) 7. Change the multimeter setting to the most appropriate ohms (Ω) scale (less than 500 ohms for small resistors). DISCONNECT the resistors for the resistance measurements. Zero the meter by touching the two probes together before each measurement. Measure resistance across each of the two resistors. Record the answers in the data table. PARALLEL CIRCUIT MEASUREMENT QUESTIONS DO THE MATH 1. Use the reciprocal formula to calculate the total resistance (R T ) of the parallel circuit. Report all answers to two significant figures. ohms 2. Calculate total current (I T ). amperes 3. Check Ohm's law as it applies to each of the two parallel circuit paths you just built and measured. Using your measured values, does the total voltage (the voltage across one dry cell) equal the current times the resistance for each circuit path? In other words, does V T = I 1 R 1 and does V T = I 2 R 2 (within a 5 percent margin of error)? a. Yes b. No 4. How does the total voltage (the voltage of one dry cell) compare with each resistor voltage? a. The total (dry cell) voltage is higher than the voltage across each resistor. b. The total (dry cell) voltage is lower than the voltage across each resistor. c. The total (dry cell) voltage is the same as the voltage across each resistor. 5. Does the current entering a circuit junction (reading 1) equal the sum of the currents leaving the junction (reading 2 + reading 4)? a. Yes b. No Activity 10 - Page 6/6

24 ACTIVITY 11 USING CBLS AND PROBES TO MEASURE VOLTAGE AND CURRENT BACKGROUND In this activity you'll have a chance to use the Texas Instruments Calculator-Based Lab (CBL2) with a graphing calculator (for example, the TI-83+) and voltage and current probes to test Ohm's and Kirchoff's laws for series circuits with mixed loads. Make sure you first review the previous activities Series Circuit Calculations, Parallel Circuit Calculations, Using Meters, and Advanced Meter Measurements so that you are completely familiar with how to perform calculations and measurements, including which probe to connect in series with the circuit and which to connect in parallel across the device to be measured. PART 1 - CBL SYSTEM SETUP A calculator-based lab (CBL) system consisting of a graphing calculator, a CBL interface, and a voltage probe. A. Setting up the Graphing Calculator for Voltage and Current Measurements 1. Make sure the TI-83+ calculator is firmly linked via cable to the CBL2. 2. Plug the voltage probe into Channel 1 (CH 1) of the CBL2. 3. Turn on the TI-83+ calculator. 4. Press the blue APPS button. 5. Select the DataMate program. 6. Press 1 for Setup. a. Press ENTER if CH 1: doesn't display your connected sensor. b. Press 7 until you see the desired sensor, then press its number. 7. Cursor to the fifth line (MODE choice) and press ENTER to program the type of data recording you'd like to do (e.g., EVENTS WITH ENTRY) by pressing the number in front of the desired choice. (IMPORTANT: Do not cursor for this choice or you'll be bounced back to the previous page.) Activity 11 - Page 1/5

25 ACTIVITY 11 USING CBLS AND PROBES TO MEASURE VOLTAGE AND CURRENT PART 1 CBL SYSTEM SETUP (CONTINUED) 8. Press 4 to SAVE your settings as a named program (e.g., VOLT) so that you can use it again (type the name using calculator keys corresponding to the alphabet letters in green at the upper right of the keys). 9. When your setup is complete, press 1 for OK. 10. Press 2 to LOAD the desired experiment. Select the experiment name, VOLT. 11. After you have connected the red lead of the voltage probe to the positive side of the first (bottom) dry cell and the black lead to the negative side of the dry cell, press 2 to start your experiment. You will press ENTER to collect each data point. Then enter consecutive numbers for each reading you collect (for example, 1-5 for readings 1 through 5) and press ENTER to continue. 12. Press the black STO key to end the experiment. Your times or entered numbers will be in list L1, and your data will be list L View and record your data or store them in a named list before doing additional data collection. EXTEMELY IMPORTANT: Every time you run an experiment, the calculator reuses and thus ERASES all data previously stored in lists L1 and L2. To save these data lists before running a second experiment, follow the directions below for Viewing Lists of Numbers and Saving Data to Named Lists. 14. To collect current data, repeat steps 1-13 above, substituting the current probe for the voltage probe and using the program name, CURRENT. Remember to connect the red side of the current probe in series toward the positive side of the dry cell for each current reading. VIEWING LISTS OF NUMBERS 1. Press ENTER, then 6 to quit the DataMate program. 2. Press the black STAT key in the green ALPHA key row. 3. Press ENTER or 1 to select Edit. This will display your data lists. The X variable data you set (for example, time or event number) will be in list L1, and the Y variable data measured will be in L2 (and in sequential lists if more than one sensor was used). Activity 11 - Page 2/5

26 ACTIVITY 11 USING CBLS AND PROBES TO MEASURE VOLTAGE AND CURRENT PART 2 WIRING AND MEASUREMENT DIRECTIONS A. Measuring Voltage in a Series Circuit Materials per group of two to four students: six pieces of insulated copper wire, two 1.5-volt dry cells and holders, one graphing calculator, one TI-CBL2, one voltage probe, one current probe, one 47-ohm resistor, two lightbulbs and holders, 8-10 alligator or Fahnstock clips 1. Make a circuit connecting the two lightbulbs, resistor, and two 1.5-V dry cells in series. Place the resistor between the negative end of the dry cells and the two lightbulbs. The circuit should be closed as indicated by the bulbs lighting. Complete all series voltage measurements before doing the series current measurements. Your circuit should look something like this, with more looped than rectangular wires. 2. Make sure your calculator is on and the VOLT program is loaded and started. Attach the voltage probe leads across the bottom dry cell to measure the voltage, making sure to connect the positive ends and the negative ends to the correct sides as indicated on the dry cell. By convention we use the red wire to connect positive sides and the black wire to connect negative sides of devices. Record the voltage displayed on the meter in the Series Circuit Data Table after dry cell 1. SERIES CIRCUIT DATA TABLE Measurement Voltage (V) Current (A) Calculated Resistance (Ω) Dry cell 1 Do not calculate should be zero Dry cell 2 Do not calculate should be zero Lightbulb 1 Lightbulb 2 Resistor Activity 11 - Page 3/5

27 ACTIVITY 11 USING CBLS AND PROBES TO MEASURE VOLTAGE AND CURRENT PART 2 WIRING AND MEASUREMENT DIRECTIONS (CONTINUED) 3. Repeat the voltage measurement across the second dry cell. Enter the voltage in the table. 4. Repeat the voltage measurement across lightbulb 1, lightbulb 2, and the resistor. Record the voltages. B. Measuring Current in a Series Circuit A calculator-based lab (CBL) system consisting of a graphing calculator, a CBL interface, and a current probe. 1. For current you'll need to change probes and load the CURRENT program. 2. Break your circuit between each device in order to insert the current probe. For current measurements insert the probe just to the right of or below the named object in the table. 3. Complete the table by applying Ohm's law to calculate the resistance of each load. PART 3 - SERIES CIRCUIT QUESTIONS 1. Apply Ohm's law, R T = V T / I T, to calculate the total resistance of this circuit, which contains three loads (two lightbulbs and one resistor). What is the total resistance of the circuit? ohms 2. Does total voltage (the voltage of the sum of the dry cells) equal the sum of the voltages across each load (within 2 percent for measurement error)? a. Yes b. No 3. Are currents equal anywhere you try to measure them? a. Yes b. No 4. Does total resistance calculated from R T = V T / I T equal the sum of the calculated individual resistances? a. Yes b. No Activity 11 - Page 4/5

28 ACTIVITY 11 USING CBLS AND PROBES TO MEASURE VOLTAGE AND CURRENT TI-83+ OPERATION APPENDICES If the DataMate program isn't found within your CBL2 applications: 1. Make sure the TI-83+ calculator is firmly linked via cable to the CBL2. 2. Press the yellow 2nd button, then the LINK button just below and right of 2nd. 3. Cursor to highlight the word RECEIVE. 4. Press the blue ENTER button. Waiting should appear on the screen. 5. Press TRANSFER on the CBL2. The TI-83+ screen will say done when all the needed DataMate files have been transferred to the calculator. Saving Data to Named Lists 1. Cursor onto the heading of the first alphabet list (... 1A). 2. On the bottom of the TI screen, you'll see NAME=. Type in a short, descriptive name such as TEMP1 or TEMP2. (The A in 1A indicates you are in alphabet mode. You can toggle in and out of alphabet mode by pressing the green ALPHA key. Pressing 2nd then ALPHA puts you in caps lock mode.) 3. When finished typing the name, press ENTER. Now, while still on the new name, you'll see the "new name=" on the bottom of the TI display. Press 2nd then 1 to copy the data from list L1 into your named list. 4. Repeat the three steps above to copy data in other lists. (Remember, the data in L1 the X or independent variable will remain the same for repeat runs of the same experiment, so this list needs to be saved only once.) Clearing a List 1. Cursor onto the list column heading. 2. Press the CLEAR, then ENTER buttons. Link Error Message If you see a "Link Error" message on your TI-83+ screen, make sure that all your cable connections, including the probe connection, are secure. Restart the calculator and follow the setup directions. If you receive the same error message again, it may mean that your CBL2 or calculator dry cells (AA dry cells) need to be changed. It is advised that you remove and replace one dry cell at a time when dealing with electrical devices containing stored programs. Activity 11 - Page 5/5

29 ACTIVITY 12 USING CBLS AND PROBES FOR MIXED CIRCUIT MEASUREMENTS BACKGROUND In this activity you'll have a chance to use the Texas Instruments Calculator-Based Lab (CBL2) with a graphing calculator (for example, the TI-83+) and voltage and current probes to test Kirchoff's laws in a mixed circuit. Make sure you first review the previous activity, Using CBLs and Probes to Measure Voltage and Current, so that you are completely familiar with how to use the CBL2 DataMate program, connect the voltage and current probes to perform the measurements, and view and save your data. PART 1 CBL SYSTEM SETUP A calculator-based lab (CBL) system consisting of a graphing calculator, a CBL interface, and a voltage probe. Note that the voltage probe is connected in parallel with the dry cell, with the red wire connected to the positive terminal and the black wire connected to the negative terminal. Use the same VOLT and CURRENT programs as in the previous activity. 1. Make sure the TI-83+ calculator is firmly linked via cable to the CBL2. 2. Plug the voltage probe into Channel 1 (CH 1) of the CBL2. 3. Turn on the TI-83+ calculator. 4. Press the blue APPS button. 5. Select the DataMate program. 6. Press 2 to LOAD the desired experiment. Select the experiment named VOLT. Activity 12 - Page 1/4

30 ACTIVITY 12 USING CBLS AND PROBES FOR MIXED CIRCUIT MEASUREMENTS PART 1 CBL SYSTEM SETUP (CONTINUED) 7. Press 2 to start your experiment. You will press ENTER to collect each data point. Then enter consecutive numbers for each reading you collect (for example, 1-5 for readings 1 through 5). 8. Press the black STO key to end the experiment. Your times or entered numbers will be in list L1, and your data will be list L2. 9. View and record your data or store them in a named list before doing additional data collection. EXTREMELY IMPORTANT: Every time you run an experiment, the calculator reuses and thus ERASES all data previously stored in lists L1 and L2. To save these data lists before running a second experiment, follow the Activity 11 directions for Viewing Lists of Numbers and Saving Data to Named Lists. 10. To collect current data, repeat steps 1-9 above, substituting the current probe for the voltage probe and using the program named CURRENT. A calculator-based lab (CBL) system consisting of a graphing calculator, a CBL interface, and a current probe. Note that the current probe is inserted inside of, and in series with, the circuit. The red side of the current probe connects to the positive terminal of the dry cell. Activity 12 - Page 2/4

31 ACTIVITY 12 USING CBLS AND PROBES FOR MIXED CIRCUIT MEASUREMENTS PART 2 WIRING AND MEASUREMENT DIRECTIONS You may find it helpful to review the formulas for parallel circuits in the Parallel Circuit Calculations computer activity and in Review Sheet 2 before you begin. Materials per group of two to four students: one CBL2, one graphing calculator, one voltage probe, one current sensor, two dry cells and holders, two lightbulbs and holders, one 47-ohm resistor, eight pieces of insulated copper wire, 5-10 alligator or Fahnstock clips 1. Build the mixed parallel circuit pictured below using two dry cells, two lightbulbs, and one 47-ohm resistor. First, wire the two dry cells in series, connecting one cell's positive terminal to the other's negative terminal. Next wire the first lightbulb in series with the dry cells. Finally, wire the resistor and second lightbulb in series with each other and in parallel with the first lightbulb. Your mixed circuit should look something like this, with more looped than rectangular wires. 2. Remember to connect the red voltage probe lead to the positive side of a dry cell (or to the side of an object connected to the positive side of a dry cell). Measure the voltage across each object and enter the results in the Mixed Circuit Data Table. MIXED CIRCUIT DATA TABLE Reading Measurement Voltage (V) Current (A) Calculated Resistance (Ω) 1 Dry cell 1 Should be zero 2 Dry cell 2 Should be zero 3 Lightbulb 1 4 Lightbulb 2 5 Resistor 3. For current measurements change to the CURRENT probe and program, then insert the probe into the circuit as pictured. Record your data. Locations for current measurements are represented by the ammeter symbol, a circled A. 4. Use V 1 = I 1 x R 1, and V 2 = I 2 x R 2, etc. to calculate the resistances of the three loads. Activity 12 - Page 3/4

32 ACTIVITY 12 USING CBLS AND PROBES FOR MIXED CIRCUIT MEASUREMENTS PART 3 MIXED CIRCUIT CALCULATIONS Apply Ohm's and Kirchhoff's laws and the reciprocal formula for resistance in parallel circuits to calculate the values in the Mixed Circuit Calculations Table. Use your data from the previous table. MIXED CIRCUIT CALCULATIONS TABLE Calculation Total voltage across circuit path 1 containing lightbulb 1 Total voltage across circuit path 2 containing resistor and lightbulb 2 Total current through circuit path 1 containing lightbulb 1 Total current through circuit path 2 containing resistor and lightbulb 2 Total resistance of circuit path 1 containing lightbulb 1 Total resistance of circuit path 2 containing resistor and lightbulb 2 Total voltage of the entire mixed circuit Total current of the entire mixed circuit Total resistance of the entire mixed circuit (use the reciprocal formula) Voltage (V), Current (A), or Resistance (Ω) PART 4 - MIXED CIRCUIT QUESTIONS Try to verify Kirchhoff's laws. For each of the questions below, record the letter of the correct answer from these choices in front of each question number. a. The total is greater than that of the circuit path. b. The total is less than that of the circuit path. c. The total is the same as that of the circuit path. 1. How does the total voltage across the mixed circuit compare to the voltages across circuit path 1? 2. How does the total voltage across the mixed circuit compare to the voltages across circuit path 2? 3. How does the total current of the mixed circuit compare to the current through circuit path 1? 4. How does the total current of the mixed circuit compare to the current through circuit path 2? 5. How does the total resistance of the mixed circuit compare to the total resistance of circuit path 1? 6. How does the total resistance of the mixed circuit compare to the total resistance of circuit path 2? Activity 12 - Page 4/4