Series and Parallel rev617 PDF

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Circuits Series and Parallel Circuits Objectives

Study current flow in series and parallel circuits Study voltages in series and parallel circuits Use Ohm’s law to calculate equivalent resistance of series and parallel circuits

Equipment

Computer with LoggerPro LabQuest Two current probes One voltage probe DC power supply

Two 10 Ω resistors Two 51 Ω resistors Two 68 Ω resistors Momentary contact switch

Theory Components in an electrical circuit are in series when they are connected one after the other, so that the same current flows through both of them. Components are in parallel when they are in alternate branches of a circuit. Series and parallel circuits function differently. You may have noticed the differences in electrical circuits you use. When using some decorative holiday light circuits, if one lamp burns out, the whole string of lamps goes off. These lamps are in series. When a light bulb burns out in your house, the other lights stay on. Household wiring is normally in parallel. You can monitor these circuits using a Current and Voltage Probe System and see how they operate. One goal of this experiment is to study circuits made up of two resistors in series or parallel. You can then use Ohm’s law to determine the equivalent resistance of the two resistors.

S e rie s R e s is to rs

P a r a lle l R e s is to r s

The value of a resistor is determined by reading a color code of three or four stripes on the body of a resistor. Each color has been assigned a number from 0 through 9 and the code is determined by the formula AB×10C ± D%. The values for A, B, C and D are determined according to the diagram and table below.

Number 0 1 2 3 4 5

Color Black Brown Red Orange Yellow Green

A B C Number 6 7 8 9 5% 10% 20%

D Color Blue Violet Grey White Gold Silver No Band

Preliminary Analysis Rev. 6/17 SL

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Circuits Calculate the values in the following tables. Table 1 Configuration R1 (Ω) R2 (Ω) Parallel 10 10 10 51 Series 10 10 10 51

RTotal (Ω)

Table 2 Labeled resistor value (Ω)

Tolerance (%)

Minimum resistance (Ω)

Maximum resistance (Ω)

Procedure Part I Series Circuits 1. Go to File→Open→_Physics with Vernier →”23a Series Parallel Circ.cmbl”. Current and voltage readings will be displayed in meter windows. Click on the LabQuest button and make sure that CH1 is reading “Voltage (+/- 10 V)” and CH2 is reading “Current Probe”. 2.

Connect a Voltage Probe to Channel 1 on the LabQuest. Connect a Current Probe to Channel 2. Figure 1 LabPro Power Supply

Computer

-+ R1

R2 Current

Contact switch

Connect together the two voltage leads (red and black) of the Voltage Probe. Click “ Zero” then click OK. This sets the zero for both probes with no current flowing and with no voltage applied. Repeat steps 4 through 8 using the values for R1 and R2 in the table below. 3.

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Circuits

Table 3: Series Circuits R1()

R2 ()

1 0 1 0 5 1

1 0 5 1 5 1

1 2 3

I (A)

V1(V)

V2(V)

Req()

VTOT (V)

Req () theoretical (from Table 1)

4.

Connect the series circuit shown in Figure 1 using the 10 resistors for resistor 1 and resistor 2. Be careful that your voltage probe leads do not touch the leads connected to the resistors. Notice the Voltage Probe is used to measure the voltage applied to both resistors. The red terminal of the Current Probe should be toward the + terminal of the power supply. Set your power supply to approximately 3V.

5.

For this part of the experiment, you do not even have to click on the “ Collect” button. You can take readings from the meter windows at any time. To test your circuit, briefly press on the switch to complete the circuit. Both current and voltage readings should increase. If they do not, recheck your circuit.

6.

Press and hold the switch to complete the circuit again and read the current ( I) and total voltage (VTOT). Record the values in the data table.

7.

Connect the leads of the Voltage Probe across resistor 1 only. Do not remove resistor 2. Press and hold the switch to complete the circuit and read this voltage ( V1). Record this value in the data table.

8.

Now, connect the leads of the Voltage Probe across resistor 2 only. Press and hold the switch to complete the circuit and read this voltage ( V2). Record this value in the data table.

Part II Parallel circuits 1. Connect the parallel circuit shown in figure 2 (below) using 51 resistors for both resistor 1 and resistor 2. As in the previous circuit, the Voltage Probe is used to measure the voltage applied to both resistors. The red terminal of the Current Probe should be toward the + terminal of the power supply. The Current Probe is used to measure the total current in the circuit.

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Circuits

LabPro Power Supply

Computer

-+

R1 Current

R2

Contact switch

Figure 2 Repeat steps 2 through 5 using the values for R1 and R2 in the table below. Part 4: Parallel Circuits R1()

R2 ()

1 0 1 0 5 1

1 0 5 1 5 1

1 2 3

I (A)

V1(V)

V2 (V)

Req()

VTOT (V)

Req () theoretical from Table 1

2.

As in Part I, you can take readings from the meter windows at any time. To test your circuit, briefly press on the switch to complete the circuit. Both current and voltage readings should increase. If they do not, recheck your circuit.

3.

Press and hold the switch to complete the circuit again and read the total current ( I) and total voltage (VTOT). Record the values in the data table.

4.

Connect the leads of the Voltage Probe across resistor 1only. Press and hold the switch to complete the circuit and read the voltage (V1) across resistor 1. Record this value in the data table.

5.

Connect the leads of the Voltage Probe across resistor 2 only. Press and hold the switch to complete the circuit and read the voltage (V2) across resistor 2. Record this value in the data table.

Part III Currents in Series Circuits 1. For Part III of the experiment, you will use two Current Probes. Open the file “Exp 23b Series Parallel Circ.cmbl” from the _Physics with Vernier experiment files of Logger Pro. Two graphs of Rev. 6/17 SL

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Circuits current vs. time are displayed. The vertical axis of both graphs has current scaled from – 0.6 to + 0.6 A. The horizontal axis of both graphs has time scaled from 0 to 10 s. 2. Disconnect the Voltage Probe from Channel 1 and plug in a second Current Probe. Check to be sure the LabQuest is reading 2 current probes by clicking on the LabQuest button. 3. With nothing connected to either probe, click “ Zero” then click OK. This adjusts the current reading to zero with no current flowing. Repeat steps 4 to 6 fro the compinations of resistors in the following table Table 5: Series Currents R1()

R2 ()

1

10

51

2

51

51

I1 (A)

I2 (A)

4. Connect the series circuit shown in Figure 3. The Current Probes will measure the current flowing into and out of the two resistors. The red terminal of each Current Probe should be toward the + terminal of the power supply. LabPro Power Supply

Computer

-+ R1

R2 Current

Current

Contact switch

Figure 3 5.

Click on the “ Collect” button, wait a second or two, then press on the switch to complete the circuit. Release the switch just before the graph is completed.

6.

Select the region of the graph where the switch was on by dragging the cursor over it. Click on the Statistics button, , and record the average current in the table above. Determine the average current in the second graph following the same procedure. Change the scale on each graph to better see the currents if they are small.

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Circuits Part IV Currents in Parallel Circuits 1. Connect the parallel circuit as shown in Figure 4 using the combinations of resistors in the Table below. Table 6: Parallel Currents R1() 1

R2 ()

10

I1 (A)

I2 (A)

51

2 51 51 The two Current Probes will measure the current through each resistor individually. The red terminal of each Current Probe should be toward the + terminal of the power supply. Repeat steps 2 to 3 below for each combination of resistors.

LabPro Power Supply

-+

Computer

R1 Current

Current

R2

Contact switch

Figure 4 3.

Click on the “ Collect” button and wait a second or two. Then press on the switch to complete the circuit. Release the switch just before the graph is completed.

4.

Select the region of the graph where the switch was on by dragging the cursor over it. Click on the Statistics button, , and record the average current in the data table. Determine the average current in the second graph following the same procedure. Again, you may wish to change the scale on your graphs to better see the data.

Analysis Rev. 6/17 SL

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Circuits 1.

Looking across all of the results fill in the following table Configuration Behavior Relationshio of V 1∧V 2 ¿ V tot Series

Relationshio of I 1∧I 2

Relationshio of V 1∧V 2 ¿ V tot

Parallel

Relationshio of I 1∧I 2

2.

For each of the three series and parallel circuits in compare the experimental results with the resistance calculated in the table below. Calculate the minimum and maximum resistance of your combination using the tolerance values in Table 2. Indicate whether your measured total resistance is within the limits calculated using the resistor tolerances. Configuration R1 Series

Parallel

3.

10 10 51 10 10 51

R2

Measured

Calculated

Rtotal

Rtotal

() from Tables 3 or 4

() from Table 1

10 51 51 10 51 51

Why do you think any out of range values were obtained?

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Tolerance Limits Min Max

Rtotal

Rtotal

In Tolerance (Y or N)

Circuits

4.

If the two measured currents in your parallel circuit were not the same, which resistor had the larger current going through it? Why? Support your answer with a calculation.

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