activity 4 – building series and parallel...

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Activity 4 - /3

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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, sixpieces 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 circuitsusing 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 circuitboard will help you keep your wiring in a rectangular pattern. (Christmas tree lights makegood sources for lightbulbs.)

2. Record how the brightnesses of the bulbs in the series and parallel circuits change as youincrease 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 fromthe neat rectangular diagrams shown above (rectangles will look more like circles).

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Activity 4 - /3

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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?


4. What do you think these lighting differences suggest about the voltage across the bulbs inseries 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 inparallel 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.

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Activity 4 - /3

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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 inseries?


7. What happens to the brightness of the three bulbs wired in series as you add a dry cell inparallel with the first one?


8. What happens to the brightness of the three bulbs wired in parallel as you add a dry cell inseries with the first one?


9. What happens to the brightness of the three bulbs wired in parallel as you add a dry cell inparallel with the first one?


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Activity 8 - Page 1/3

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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 fromeither end of the corridor. The two switches are actually wired to each other as well as to thelight 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 ofboth series and parallel wiring.

A single-pole, double-throw switch is the kind of switch (for example, a light switch) found ateach entrance of rooms with two entrances. The switches are wired both to the light and to eachother on each side of the hallway. That makes a different circuit for each position of the firstswitch. 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 tothe other switch as well as the one to the light. This way, when the other switch is thrown, it willperform the desired function.

Wiring diagram of a three-way or single-pole, 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 switchmight look like.

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WIRING CHALLENGE (CONTINUED)

PREDICTIONS

For the diagram below, predict whether the light will be on or off when the switches are in thefollowing 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 roommight look like.

1. Build two switches, one for each end of the room, using three metal brads inserted into anindex card. The middle brad should be inserted through the end of a paper clip. Washerssecure the brads on the back side of the index card. The other two brads should be exactlythe length of the paper clip away. When the paper clip swings in both directions, it should beable to make solid contact with the other two brads.

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WIRING CHALLENGE CONTINUED

2. Wire a "shoebox room" with one switch on each end. Use either a shoebox or shoebox lid asthe 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 1points 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 "paperclip switch" was left in the middle position shown, touching neither point C nor point D?

a. Always On b. Always Off

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ACTIVITY 9 – USING METERS

BACKGROUND

Voltmeters are connected across the device whose voltage you wish to determine. The redwire 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 wireis connected to the negative end of the voltmeter and the negative side of the power source orother 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 beingmeasured (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 fromthe ammeter is usually connected to the positive terminal of the power source (battery, solarcell, 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 thecircuit.

AMMETER WIRED IN SERIES TO A D-CELL AND

A RESISTOR IN A CLOSED CIRCUIT.

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ACTIVITY 9 – USING METERS (CONTINUED)

OHMMETERS are connected across the device whose resistance you wish to determine - withthe device DISCONNECTED from its power source (battery). Touch the two meter probestogether before measuring the desired object's resistance to zero the meter. The red wire of theohmmeter is connected to one end of the load (the negative side), and the black wire isconnected to the other (positive) side of the load (lightbulb, resistor, etc.). Basically, you arewiring the ohmmeter in series with the load. Resistance is measured with an OPEN circuit sothat NO current is flowing through the device except that coming from the ohmmeter. DO NOTmeasure 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, 10-100) that youneed to preset by turning a dial. Most of the time we will be working with low quantities ofvoltage, current, and resistance (1-6 volts, 0-200 milliamps, 0-500 ohms).

Choose the meter setting closest to BUT GREATER THAN the value you expect to beworking 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 means1/1,000. Thus, 1 mA = 0.001 A. For Ohm's law calculations, you will need to convert yourmilliamp readings back to amps. This is the same as dividing milliamps by 1,000, or sliding thedecimal three positions to the left. For example, 28.5 mA = 0.0285 A.

For the ohmmeter used to measure resistance, you may see X1K or X10. This means that themeter 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 theneedle with its reflection to obtain the most accurate reading. Digital meters display their resultsas numbers.

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METER SETTINGS CONTINUED

The numbers you'll be working with are small (no more than 6 volts DC, no more than 250milliamps of current, and no more than 500 ohms of resistance) so that they will work with theDC 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 ison one of the bulging ends of the resistor. The first band's number is the first number of theresistance value. The second band's number is the second number of the resistance value. Thethird band represents the number of zeros following the first two numbers. People often forgetthat a third band zero value means the resistor has only TWO numbers with no zeros. Thefourth 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 goldhas a resistance value of 100 Ω and a range of 95 to 105 Ω. If the final band would have beensilver, 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 theanswer at the end of this activity.

Resistor values can be decoded using the table below for the first three bands. Remember thatthe third band represents the number of zeros after the first two numbers.

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DECODING COLORED RESISTOR BANDS (CONTINUED)

TABLE OF RESISTOR COLOR BAND CODES

Color Value Color ValueBlack 0 Green 5Brown 1 Blue 6Red 2 Violet 7

Orange 3 Gray 8Yellow 4 White 9

IMPORTANT METER RULES

a. Power: Turn OFF meters and disconnect circuits between readings, while changing metersettings, and after taking the last measurement.

b. Resistance: Disconnect a device from the circuit before measuring its resistance. Once themeter is set to 200-2,000 ohms (Ω), turn on the meter and touch the two probes together tozero the meter before taking the resistance measurement. Do NOT measure the resistanceof batteries or devices connected in closed circuits.

c. Current: Measure current by opening the circuit to include the ammeter probes in series. DoNOT measure current by connecting probes to both battery terminals.

d. Connections: Refer to the first four background diagrams to see how to correctly connectthe 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 actualmeasurements.

Materials (per team of two to four students): This handout, pencils, several different coloredmarkers, insulated copper wire, one battery holder BUT NO BATTERY, one multimeter, one100-Ω resistor

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PART 1 – METER POSTERS (CONTINUED)

Make three posters that include the title and four drawings (two pairs of DO and two pairs ofDON'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 measurevoltage.

2. "DON'T" CIRCUIT DIAGRAM: How NOT to connect the multimeter into the circuit tomeasure 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 bemeasuring (should be Xd out).

CURRENT (AMPS, A; OR MILLIAMPS, MA) POSTER

1. "DO" CIRCUIT DIAGRAM: How to connect the multimeter into the circuit to measurecurrent.

2. "DON'T" CIRCUIT DIAGRAM: How NOT to connect the multimeter into the circuit tomeasure 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 bemeasuring (should be Xd out).

RESISTANCE (OHMS, Ω) POSTER

1. "DO" CIRCUIT DIAGRAM: How to connect the multimeter into the OPEN circuit to measureresistance (or just measure the resistor separately).

2. "DON'T" CIRCUIT DIAGRAM: How NOT to connect the multimeter into the circuit tomeasure resistance (should be Xd out).

3. "DO" METER FACE: How to set the multimeter for the level of resistance it will bemeasuring.

4. "DON'T" METER FACE: How NOT to set the multimeter for the level of resistance it will bemeasuring (should be Xd out).

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PART 1 – METER POSTERS (CONTINUED)

Here is a sample Voltage poster. Many other diagrams would also work. Blank Dos andDon'ts sheets are attached at the end of this activity.

VOLTAGE MEASUREMENTS (IN VOLTS, V)

DO DON'T

DO DON'T

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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 youbegin.

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 inseries. The circuit should be closed.

Simple circuit with one drycell and one resistor.

Dial to the appropriate DC V (direct current voltage) setting (for example, 9 V). Attach themultimeter across the D-cell, making sure to attach the positive ends and the negative ends tothe correct sides as indicated on the meter and cell. By convention we use the red wire toconnect positive sides and the black wire to connect negative sides of devices like the voltmeterthat 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? ________

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PART 2 – WIRING AND MEASUREMENT DIRECTIONS (CONTINUED)

4. For current you will need to break your circuit. First, change the dial setting to the mostappropriate DC amps (A) scale. Look for a setting around 200 mA. Pick the most convenientlocation for breaking the circuit and reclosing it by attaching the red and black leads from themeter 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 convertfrom mA to A).

Note: See the background ammeter graphic to connect the meter. If the meter reading hasa 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 decodingthe 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 electriccurrent. 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 wouldbe expected to be anywhere between 95 and 105 ohms for the gold band, or 90 to110 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, useOhm'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?) Inother words, did you confirm Ohm's law?

_________________________________________________________________________

ANSWER TO BAND CODE QUESTION47 ± 2.35 ohms (Did you remember that the third band stands for the number of zeros followingthe first two numbers?)

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VOLTAGE MEASUREMENTS (IN VOLTS, V)

DO DON'T

DO DONT

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CURRENT MEASUREMENTS (IN MILLIAMPS, mA)

DO DON'T

DO DON'T

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RESISTANCE MEASUREMENTS (IN OHMS, Ω)

DO DON'T

DO DON'T

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ACTIVITY 10 – ADVANCED METER MEASUREMENTS

In this activity you'll have a chance to use meters to test Kirchhoff's laws for series and parallelcircuits. Make sure you have done the previous activity, Using Meters, first so that you arecompletely familiar with how to make each measurement, including when to connect the meterin series, when to connect it in parallel across the device to be measured, and when to measurewith 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 tomake each measurement (when to connect the meter in series, when to connect it in parallelacross 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 acircuit junction (intersection point) equals the sum of the currents leaving a circuit junction.

c. Resistance follows the reciprocal formula below.

1 RTotal = ----------------- 1 1 1 --- + --- + --- R1 R2 R3

d. Ohm's law remains V = I R, or VT = IT RT, and V1 = I1 R1 for circuit branch 1, V2 = I2 R2 forbranch 2, etc.

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




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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 shouldbe closed.

Note: To wire dry cells in series, connect the positive end of one to the negative end of theother.

Your series circuit should like somethinglike this, with more looped than rectangularwires.

2. Dial to the lowest DC V (direct current voltage) setting (but not lower than the voltage of yourcircuit). Attach the multimeter across the dry cell to measure the voltage, making sure toconnect the positive end and the negative end of the meter to the like sides on the dry celland circuit. By convention, we use the red wire to connect positive sides and the black wireto connect negative sides of devices. Enter your results in the table below. Measure the drycell on the left first. Then continue voltage measurements in a counterclockwise direction.

SERIES CIRCUIT DATA TABLEReading Measurement Voltage

(V)Current

(A)Calculated

Resistance (Ω)Measured

Resistance (Ω)

1 Dry Cell 1 Should be zero Do not measure2 Dry Cell 2 Should be zero Do not measure3 100-Ω Resistor —4 220-Ω Resistor RTotal:

3. Repeat the voltage measurement across the second dry cell. Enter the voltage.

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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 theright. Record the resistor voltages in the table.

5. For current, break the circuit to insert the ammeter as pictured. Close the circuit by attachingthe 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 mostappropriate DC amps (A) scale. Remember, the current through the most common smallresistors is around 0.2 A (200 mA). Enter the current in amps, which may require aconversion 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 themeter in series for each of the positions shown in the diagram below to obtain the remainingcurrent measurements.

Diagram showing locations to insertthe ammeter into the series circuit totake current readings 1 through 4.The ammeter is represented by an Awith 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 RTotal: 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 THECIRCUIT or DISCONNECT A WIRE so that the circuit is OPEN for the resistancemeasurements. Turn on the meter and zero it by touching the two probes together beforeeach measurement. Measure resistance across each of the two resistors. Record theanswers in the table above.

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




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SERIES CIRCUIT MEASUREMENT QUESTIONS – DO THE MATH

1. Does V = I R (to within 5 percent measurement error)? Compare measured and calculatedvalues 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 voltagesacross 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 RT = VT / IT equal the sum of the measuredresistances across each load? a. Yes b. No


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 paralleland 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 connectthe negative ends to each other.

Your parallel circuit should looksomething like this, with more loopedthan 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 thered 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.

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




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PARALLEL CIRCUIT (CONTINUED)

PARALLEL CIRCUIT DATA TABLEReading Measurement Voltage

(V)Current

(A)Calculated

Resistance (Ω)Measured

Resistance (Ω)

1 Dry Cell 1 Should be zero Do not measure2 Dry Cell 2 Should be zero Do not measure3 100-Ω Resistor R1:4 220-Ω Resistor R2:

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 theleft. Enter the resistor voltages.

5. For current break the circuit as pictured for reading 1 and close it by connecting the red andblack 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 (slidethe decimal three places to the left to convert from mA to A). Insert the meter into the circuitas shown below for readings 2 through 4. Record your current values.

Diagram showing locations to insert theammeter into the parallel circuit to takecurrent readings 1 through 4.

6. Use the appropriate version of Ohm's law to calculate the two resistor resistances (R1 andR2). Calculate the resistance of the first resistor (R1) using the Dry Cell 2 voltage and thereading 2 current (reading 1 is the total current). Calculate the resistance of the secondresistor (R2) using the Dry Cell 2 voltage and the reading 4 current.

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




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ACTIVITY 10 – ADVANCED METER MEASUREMENTS (CONTINUED)

7. Change the multimeter setting to the most appropriate ohms (Ω) scale (less than 500 ohmsfor small resistors). DISCONNECT the resistors for the resistance measurements. Zero themeter by touching the two probes together before each measurement. Measure resistanceacross 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 (RT) of the parallel circuit. Reportall answers to two significant figures. ______ ohms

2. Calculate total current (IT ). ______ amperes

3. Check Ohm's law as it applies to each of the two parallel circuit paths you just built andmeasured. Using your measured values, does the total voltage (the voltage across one drycell) equal the current times the resistance for each circuit path?

In other words, does VT = I1 R1 and does VT = I2 R2 (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 leavingthe junction (reading 2 + reading 4)?

a. Yes b. No

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




HANDS-ON

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 testOhm's and Kirchoff's laws for series circuits with mixed loads. Make sure you first review theprevious activities–Series Circuit Calculations, Parallel Circuit Calculations, Using Meters, andAdvanced Meter Measurements–so that you are completely familiar with how to performcalculations and measurements, including which probe to connect in series with the circuit andwhich to connect in parallel across the device to be measured.

PART 1 - CBL SYSTEM SETUP

A calculator-based lab (CBL) systemconsisting of a graphing calculator, a CBLinterface, 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 datarecording you'd like to do (e.g., EVENTS WITH ENTRY) by pressing the number in front ofthe desired choice. (IMPORTANT: Do not cursor for this choice or you'll be bounced back tothe previous page.)

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




HANDS-ON


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 itagain (type the name using calculator keys corresponding to the alphabet letters in green atthe 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 yourexperiment. You will press ENTER to collect each data point. Then enter consecutivenumbers for each reading you collect (for example, 1-5 for readings 1 through 5) and pressENTER to continue.

12. Press the black STO key to end the experiment. Your times or entered numbers will be inlist L1, and your data will be list L2.

13. View and record your data or store them in a named list before doing additional datacollection.

EXTEMELY IMPORTANT: Every time you run an experiment, the calculator reusesand thus ERASES all data previously stored in lists L1 and L2. To save thesedata lists before running a second experiment, follow the directions below forViewing Lists of Numbers and Saving Data to Named Lists.

14. To collect current data, repeat steps 1-13 above, substituting the current probe for thevoltage probe and using the program name, CURRENT. Remember to connect the red sideof 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 Yvariable data measured will be in L2 (and in sequential lists if more than one sensor wasused).

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




HANDS-ON


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-voltdry cells and holders, one graphing calculator, one TI-CBL2, one voltage probe, one currentprobe, 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. Thecircuit should be closed as indicated by the bulbs lighting. Complete all series voltagemeasurements 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 thevoltage probe leads across the bottom dry cell to measure the voltage, making sure toconnect the positive ends and the negative ends to the correct sides as indicated on the drycell. By convention we use the red wire to connect positive sides and the black wire toconnect negative sides of devices. Record the voltage displayed on the meter in the SeriesCircuit Data Table after dry cell 1.

SERIES CIRCUIT DATA TABLEMeasurement Voltage (V) Current (A) Calculated Resistance (Ω)

Dry cell 1 Do not calculate—should be zeroDry cell 2 Do not calculate—should be zeroLightbulb 1Lightbulb 2Resistor

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




HANDS-ON


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. Recordthe voltages.

B. Measuring Current in a Series Circuit

A calculator-based lab (CBL) systemconsisting of a graphing calculator, a CBLinterface, 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 currentmeasurements 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, RT = VT / IT , to calculate the total resistance of this circuit, which containsthree 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 voltagesacross 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 RT = VT / IT equal the sum of the calculated individualresistances? a. Yes b. No

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




HANDS-ON


TI-83+ OPERATION APPENDICES

If the DataMate program isn't found within your CBL2 applications:


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 neededDataMate 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 suchas TEMP1 or TEMP2. (The A in 1A indicates you are in alphabet mode. You can toggle inand out of alphabet mode by pressing the green ALPHA key. Pressing 2nd then ALPHAputs you in caps lock mode.)

3. When finished typing the name, press ENTER. Now, while still on the new name, you'll seethe "new name=" on the bottom of the TI display. Press 2nd then 1 to copy the data from listL1 into your named list.

4. Repeat the three steps above to copy data in other lists. (Remember, the data in L1—the Xor independent variable—will remain the same for repeat runs of the same experiment, sothis list needs to be saved only once.)

Clearing a List1. Cursor onto the list column heading.

2. Press the CLEAR, then ENTER buttons.

Link Error MessageIf you see a "Link Error" message on your TI-83+ screen, make sure that all your cableconnections, including the probe connection, are secure. Restart the calculator and follow thesetup directions. If you receive the same error message again, it may mean that your CBL2 orcalculator dry cells (AA dry cells) need to be changed. It is advised that you remove and replaceone dry cell at a time when dealing with electrical devices containing stored programs.

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




HANDS-ON

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 testKirchoff's laws in a mixed circuit. Make sure you first review the previous activity, Using CBLsand Probes to Measure Voltage and Current, so that you are completely familiar with how to usethe CBL2 DataMate program, connect the voltage and current probes to perform themeasurements, and view and save your data.

PART 1 – CBL SYSTEM SETUP

A calculator-based lab (CBL) systemconsisting of a graphing calculator, a CBLinterface, and a voltage probe.

Note that the voltage probe is connected inparallel with the dry cell, with the red wireconnected to the positive terminal and theblack wire connected to the negative terminal.

Use the same VOLT and CURRENT programs as in the previous activity.


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.

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




HANDS-ON

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. Thenenter consecutive numbers for each reading you collect (for example, 1-5 for readings 1through 5).

8. Press the black STO key to end the experiment. Your times or entered numbers will be inlist L1, and your data will be list L2.

9. View and record your data or store them in a named list before doing additional datacollection.

EXTREMELY IMPORTANT: Every time you run an experiment, thecalculator reuses and thus ERASES all data previously stored in lists L1 andL2. To save these data lists before running a second experiment, follow theActivity 11 directions for Viewing Lists of Numbers and Saving Data to NamedLists.

10. To collect current data, repeat steps 1-9 above, substituting the current probe for thevoltage probe and using the program named CURRENT.

A calculator-based lab (CBL) systemconsisting of a graphing calculator, a CBLinterface, and a current probe.

Note that the current probe is inserted insideof, and in series with, the circuit. The red sideof the current probe connects to the positiveterminal of the dry cell.

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




HANDS-ON


PART 2 – WIRING AND MEASUREMENT DIRECTIONSYou may find it helpful to review the formulas for parallel circuits in the Parallel CircuitCalculations computer activity and in Review Sheet 2 before you begin.

Materials per group of two to four students: one CBL2, one graphing calculator, one voltageprobe, one current sensor, two dry cells and holders, two lightbulbs and holders, one 47-ohmresistor, 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 one47-ohm resistor. First, wire the two dry cells in series, connecting one cell's positive terminalto 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 withthe first lightbulb.

Your mixed circuit should look something likethis, 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 theside of an object connected to the positive side of a dry cell). Measure the voltage acrosseach object and enter the results in the Mixed Circuit Data Table.

MIXED CIRCUIT DATA TABLEReading Measurement Voltage (V) Current (A) Calculated Resistance (Ω)

1 Dry cell 1 Should be zero2 Dry cell 2 Should be zero3 Lightbulb 14 Lightbulb 25 Resistor

3. For current measurements change to the CURRENT probe and program, then insert theprobe into the circuit as pictured. Record your data.

Locations for current measurements arerepresented by the ammeter symbol, acircled A.

4. Use V1 = I1 x R1, and V2 = I2 x R2, etc. to calculate the resistances of the three loads.

Name __________________________________ Date ________________________

Teacher ________________________________ Period ________________________




HANDS-ON


PART 3 – MIXED CIRCUIT CALCULATIONS

Apply Ohm's and Kirchhoff's laws and the reciprocal formula for resistance in parallel circuits tocalculate the values in the Mixed Circuit Calculations Table. Use your data from the previoustable.

MIXED CIRCUIT CALCULATIONS TABLE

CalculationVoltage (V),

Current (A), orResistance (Ω)

Total voltage across circuit path 1 containing lightbulb 1Total voltage across circuit path 2 containing resistor and lightbulb 2Total current through circuit path 1 containing lightbulb 1Total current through circuit path 2 containing resistor and lightbulb 2Total resistance of circuit path 1 containing lightbulb 1Total resistance of circuit path 2 containing resistor and lightbulb 2Total voltage of the entire mixed circuitTotal current of the entire mixed circuitTotal resistance of the entire mixed circuit (use the reciprocal formula)

PART 4 - MIXED CIRCUIT QUESTIONS

Try to verify Kirchhoff's laws. For each of the questions below, record the letter of the correctanswer 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 circuitpath 1?

2. How does the total voltage across the mixed circuit compare to the voltages across circuitpath 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 circuitpath 1?

6. How does the total resistance of the mixed circuit compare to the total resistance of circuitpath 2?

activity 4 – building series and parallel...

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