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Lab 32: Series and Parallel Circuits

Purpose

To build series and parallel circuits and study the differences between them

Background

Electricians are called upon whenever new buildings need electrical work. The electrician surveys the site and determines what kind of currents and voltages are required to satisfy the client’s needs. Sometimes the circuit requires components to be connected like you would in plumbing so the water could ﬂow. This is called a series circuit. Sometimes the components need to be connected in parallel, like the rungs on a ladder. Each type of circuit has its advantages. In this lab, you will study the advantages of and the differences between series and parallel circuits.

Skills Focus

Classifying, inferring, comparing and contrasting, drawing conclusions

Procedure

1. Start Virtual Physics and select Series and Parallel Circuits from the list of assignments. The lab will open in the Circuits laboratory.

2. The laboratory will be set up with a function generator set to 12 V DC already on the engineering paper, which is the schematic or plan of the circuit built on the breadboard. In this assignment, you will have to add resistors to create a circuit. To add resistors, simply click on the resistor symbol at the top of the engineering paper and drag it onto the paper. You may move resistors around by clicking them on the middle blue dot. You can also extend their leads by clicking on the end red dots and dragging them to where you want to connect them to other components. The line will be green if it is in an allowable location. You will notice that the breadboard will automatically populate with the resistors that you add to the schematic.

3. You need to build a circuit that has only one path for the current to follow.

This is called a series circuit. Use only resistors to make this circuit. On the

engineering paper, place ﬁve resistors in series using the resistor symbol at

the top. First start by connecting the ﬁrst resistor to an open end of the

function generator. Then drag out a new resistor and place it next to the

open end of the last placed resistor. Follow the same process until you have

ﬁve resistors in series. Complete the circuit by connecting the last resistor

you added to the other side of the voltage source.

4. Make sure that that there is only one path for the current to ﬂow through the resistors you connected in Step 3. After you have placed the resistors on the circuit, you will need to change the resistance of each of the resistors as speciﬁed in Step 5. You can do this by clicking on the number next to the resistor. A small box will pop up where you can adjust the value of the resistor.

5. Change the value of each resistor to the match the values found in Data Table 1. Assume that resistor 1 is the one connected to the positive side of the voltage source and resistor 5 is the one connected to the negative side of the voltage source.

Data Table 1

Resistor Number	Resistor Value ( )
1	120
2	500
3	200
4	135
5	10,000

6. Using the multimeter to measure the current and the voltages across each resistor. The symbol for the multimeter has a DMM in the middle of it. Click and drag the red lead to one side of the resistor. It should lock into place. Then click and drag the black lead to the other side of that same resistor to measure the drop in voltage across the resistor. You can read the voltage and current from the yellow multimeter display. To measure the current passing through the resistor, change the multimeter from VDC to IDC, which changes the variable being measured from voltage to current. Record your measurements in Data Table 2.

NOTE: For the ammeter to measure current, it should be placed with both leads on one side of the resistor. This is because the current must ﬂow through the ammeter to measure it. However, the voltmeter needs to compare voltages at two points, so it should be hooked up across the resistor.

Data Table 2

Resistor Number	Voltage (V)	Current (A)
1
2
3
4
5

7. Now, using the same resistors as before, you will build a parallel circuit. This is done by creating multiple paths for the current to follow. To do this, ﬁrst move all the resistors to the bottom half of the paper, but don’t delete them.

8. First add a new resistor in series to the beginning of the function generator. Change its resistance to equal 1 .

9. Drag and set the other ﬁve resistors back onto the lines so that the circuit looks like a ladder with the resistors as the steps. Your ﬁnal schematic should look like the picture on the right.

10. Using the same technique as Step 6, measure the voltage and current across each of the ﬁve resistors listed in Data Table 1. Remember that it is a DC source, so you must use the DC Voltmeter and DC Ammeter. Record your results in Data Table 3 below.

Data Table 3

Resistor Number	Voltage (V)	Current (A)
1
2
3
4
5

Analyze and Conclude

1. Classifying What are the variables in this experiment?

2. Inferring Which variables stay the same, and which change in the series circuit?

3. Which variables stay the same, and which change in the parallel circuit?

4. Comparing and Contrasting How do parallel and series circuits differ?

5. Drawing Conclusions In what way does a series circuit look like it would have the same current throughout?

6. In what way would your answer to question 4 above be important for an electrician to know?

Going Further

7. Now go back to the circuits and replace the resistors with light bulbs. The symbol for a light bulb is a white circle with an X in the middle. Place them on the engineering paper. Create a series circuit and a parallel circuit like the ones you made earlier. Then try removing one of the light bulbs. Record below what happens in each case. Also, record the relative brightnesses of the bulbs in each circuit.

ISBN 1-269-73240-4

Series and Parallel Circuits

102 Series and Parallel Circuits

ISBN 1-269-73240-4

Series and Parallel Circuits

Series and Parallel Circuits 103

ISBN 1-269-73240-4

Series and Parallel Circuits

104 Series and Parallel Circuits

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ISBN 1-269-73240-4

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