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> Home > Curriculum > Activities > Bulbs & Batteries Side by Side

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TE Activity: Bulbs & Batteries Side by Side

A black/white drawing of a table lamp with dashes coming out from the shade, indicating that the light is on.

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Summary

We are surrounded everyday by circuits that utilize "in parallel" and "in series" circuitry. Complicated circuits designed by engineers are made of many simpler parallel and series circuits. In this hands-on activity, students build parallel circuits, exploring how they function and their unique features.

Engineering Connection

Engineers apply their understanding of circuitry to the design of practical, everyday products. They often choose to use parallel circuits so that if one circuit part breaks, the rest of the circuit continues to work. For example, when designing the electrical system for cars, trucks and SUVs, electrical engineers configure the wiring system so the brake lights and headlights are connected in parallel. That way, when one of the bulbs burns out, the other headlight or brake light remains illuminated.

Contents

  1. Learning Objectives
  2. Materials
  3. Introduction/Motivation
  4. Procedure
  5. Attachments
  6. Safety Issues
  7. Troubleshooting Tips
  8. Assessment
  9. Extensions
  10. Activity Scaling

Grade Level: 4 (3-5) Group Size: 4
Time Required: 60 minutes
Activity Dependency : None
Expendable Cost Per Group : US$ 8.50
Keywords: circuit, parallel circuit, circuit diagram, electricity, electrical power, Ohm's law
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Related Curriculum

subject areas Algebra
Physical Science
curricular units Put a Spark In It! - Electricity
lessons Many Paths

Educational Standards    

  •   Colorado Math
  •   Colorado Science

Learning Objectives (Return to Contents)

After this activity, students should be able to:

  • Define, recognize and assemble parallel circuits and parallel sections of more complex circuits.
  • Understand that when loads are connected in parallel in a circuit the total resistance decreases.
  • Explain the path of electrical charge through a circuit.
  • Describe the function of a switch in a parallel circuit.
  • Describe how current changes in a parallel circuit when a light bulb is removed from or added to the circuit.
  • Describe how current changes when batteries are added in parallel or removed from a parallel arrangement.
  • Demonstrate the process of measuring using the appropriate units in removing insulation from wire.
  • Describe the connections among representations of circuit symbols.
  • Draw parallel circuits using symbols.
  • Understand equations to calculate electrical power.
  • Use appropriate computational techniques to solve problems using Ohm's law for parallel circuits.
  • Use appropriate computational techniques to solve electric power problems.

Materials List (Return to Contents)

Each group needs:

For the entire class to share:

  • Rubber bands
  • Wire strippers or sandpaper (to remove insulation at wire ends)
  • Wire cutters
  • Screwdriver

Note: Many of the materials required for this lab can be reused in numerous other electricity activities. When the batteries wear out, dispose of them at a hazardous waste disposal site.

Introduction/Motivation (Return to Contents)

Ask the students if any of them have ever been taking a shower when someone in another part of the house flushed a toilet — OUCH! The water in the shower becomes very hot because you were forced to share cold water with another device in the house. A parallel circuit works in a similar way. When two devices are connected in parallel, they are forced to share the current that is flowing through the circuit.

Ask the students if any of them have a lamp at home that uses a three-way light bulb? (Some will answer yes.) For those students who are not familiar with a three-way light bulb, explain that it has three bulb filaments, providing a low, medium and high brightness setting, for example, 60 watts / 75 watts / 100 watts. With each click of the lamp, the light bulb gets brighter. Ask the students who have a three-way light bulb at home if they have ever had the middle level of brightness not work, but the lowest level and highest level still work? (A student may answer yes.) Remind students that when they built circuits that were in series, when one light bulb was taken out of the series circuit, an open circuit was created and the electrons could not flow to light the other bulbs. Now ask the students, how is it possible that when the middle level of brightness does not work in a three-way light bulb, the lowest level and highest level still work? (Answer: The electrons can still flow to the other two filaments because the three filaments are connected in parallel.) Explain to students that the filaments in a three-way light bulb are connected as an "in parallel" circuit.

As another example, tell students that when designing the electrical system for cars, trucks or SUVs, electrical engineers design the wiring system so the brake lights and headlights are connected in parallel. That way, when one of the bulbs in a headlight or brake light burns out the other headlight or brake light remains illuminated. Headlights and brake lights are only a few examples of the many devices that engineers connect in parallel. Engineers use parallel circuits often to make sure that if one circuit part breaks, the rest of the circuit continues to work.

On the left, a drawing of a parallel circuit constructed with a battery, two light bulbs, two light bulb holders, a switch and wires linking the components. The corresponding circuit diagram on the right: lines represent wires, circles with an "X" inside represent the light bulbs and light bulb holders, two lines perpendicular to the wire and of different lengths represent the battery, and a short line at a 45 degree angle to the wire represents the switch.
Figure 1. A parallel circuit (left), and its corresponding circuit diagram (right).
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Background — Parallel Circuits

  • Since each device connects across the same two nodes (a point where two wires intersect), the voltage across each device is the same.
  • The total resistance for a parallel circuit is less than the resistance of any one branch.
  • From Ohm's law (I = V / R), the total current is equal to the voltage divided by the total resistance.
  • The total current divides among parallel branches. Branches with lower resistances have higher current, while branches with higher resistances have lower current.
  • The total current is equal to the sum of the currents in the branches.
  • The total voltage for identical batteries connected in parallel is the same as the voltage across any one battery.
  • Engineers connect things in parallel so that if one circuit part breaks the rest of the circuit still works.

Before the Activity

  • Assemble all the materials. If you conducted the series circuit activity (Lesson 5, Bulbs and Batteries in a Row), reuse the wires, light bulbs, light bulb holders and batteries from that activity.
  • Cut four 6 in (15 cm) pieces, two 10 in (25 cm) pieces, and one 4 in (10 cm) pieces for each team.

With the Students

  1. Ask students to predict how many batteries it will take to light the two light bulbs and record their prediction on the Side by Side Worksheet.
  2. Have the students use the wire strippers or sandpaper to remove about 1/2 in (1.3 cm) of the insulation from the ends of each wire piece.
  3. Have each team make a battery holder. Using masking tape, connect two D-cell batteries in series. The positive terminal of one battery should be touching the negative terminal of the second battery. Cut a paper towel holder to fit the length of the two batteries. Place the two batteries in the paper towel tube. Connect a 10-in wire to the positive terminal of one battery and another 10-in wire to the negative terminal of the second battery.
  4. Construct a circuit using the two batteries in series, a switch, and two light bulb holders and light bulbs in parallel (see Figure 2). Close the switch. What happens? (Answer: Both bulbs light up.)

A photograph of a parallel circuit made with two D-cell batteries, two light bulb holders, two light bulbs and a switch. The two D-cell batteries are contained within a cardboard paper towel tube. One wire leads from the tube to the switch, which is made from two thumbtacks and a paper clip. Another wire exits the opposite end of the tube and is connected to one of the light bulb holders. The two light bulb holders are connected in parallel using short wires. The switch is closed and the two light bulbs are lit.
Figure 2. A parallel circuit with two light bulbs.
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  1. Open the switch and remove one of the light bulbs from its holder. Close the switch. What happens? (Answer: The bulb remaining in the circuit lights up. See Figure 3.)

A photograph of a parallel circuit made with two D-cell batteries, two light bulb holders, two light bulbs and a switch. The two D-cell batteries are contained within a cardboard paper towel tube. One wire leads from the tube to the switch, which is made from two thumbtacks and a paper clip. Another wire exits the opposite end of the tube and is connected to one of the light bulb holders. The two light bulb holders are connected in parallel using short wires. The switch is closed. Although one light bulb is removed from its holder, the remaining light bulb is still lit.
Figure 3. A parallel circuit with one light bulb removed, and one light bulb remaining in the circuit.
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  1. Open the switch and replace the light bulb you removed. Now remove the other light bulb. Close the switch. What happens? (Answer: The bulb now in the circuit lights up.)
  2. Open the switch. Replace the bulb you removed and add a third light bulb in parallel with the first two. Close the switch to test the circuit. What happens? (Answer: Each of the three bulbs is just as bright as when there were only two bulbs.)
  3. Use one team's circuit and demonstrate what happens to the brightness of the bulbs as you add a fourth bulb in parallel. What happens? (Answer: The fourth bulb is just as bright as the first three. Also, the first three bulbs are just as bright as they were before.)
  4. Use the knowledge you have gained about parallel circuits to complete the Electric Power Math Worksheet and Parallel Circuit Math Worksheet. Or, if time is limited, assign for homework.

Safety Issues (Return to Contents)

  • Ask students not to play with the light bulbs or holders. If either of these items break, they can cause injury.
  • Ask students not to play with the insulated wire; they may cut or poke themselves or others.

Troubleshooting Tips (Return to Contents)

To help students understand the equation on the Electric Power Math Worksheet, review it with them and ask them to find the "missing variable."

There must be good electrical contact between all the circuit components. If students have difficulty getting the circuit to work, check all the connections.

Pre-Activity Assessment

Human Diagram: Ask for three volunteers. Assign one volunteer to be the "battery" and two as 'light bulbs." (It may help to draw the appropriate symbols on pieces of paper and tape them to their shirts.) Have the students physically portray a series circuit by holding hands in a circle. Then have the students portray a parallel circuit by having the light bulbs and battery stand facing one direction with their arms touching the elbows of the person in front of them.

Prediction: Hand out the Side by Side Worksheets before the activity begins. Have students predict how many batteries they think it will take to light the two light bulbs, and record their prediction on the worksheet.

Activity Embedded Assessment

Worksheet: Hand out the Side by Side Worksheets before the activity begins and ask students to follow along, first diagramming the series circuit they construct, then filling in answers as they work through the activity.

Post-Activity Assessment

Roundtable: Have the class form into teams of 3-5 students each. Have the students on each team make a list of objects that might have parallel circuits in them by each person taking turns writing down ideas. Students pass the list around the group until all ideas are exhausted. Have teams read aloud the answers and write them on the board. (Possible items: Lights in a house, appliances, computers, toys, CD players, cell phones, etc.)

Make It Fun with Boggle!: Repeat the same activity as above, except when the teams read aloud their answers and write them on the board, ask if any other teams came up with the same idea. If any other teams have the same answer on their sheet, all teams have to cross that answer out on their list. The team that ends up with the most "unique" ideas, wins!

Problem Solving/Homework: Have students complete the Electric Power Math Worksheet and Parallel Circuit Math Worksheet.

Activity Extensions (Return to Contents)

Use one team's circuit and insert a third battery in parallel. Use a multimeter to measure the voltage across the two batteries. How does it compare to the voltage of one D-cell battery? (Answer: The voltage across three identical batteries connected in parallel is the same as the voltage across two of the batteries.)

Use a multimeter to determine the voltage and current across a single light bulb, using a simple circuit with one light bulb. Use these values to find the resistance of the light bulb using Ohm's law R = V / I. Next, use the multimeter to determine the voltage across two bulbs in parallel and the current in the circuit. Find the resistance of this load using R = V / I. Compare the resistance of one bulb to the resistance of two bulbs in parallel. Compare the current in one bulb to the current in the circuit.

Note: A multimeter is an instrument that combines the measuring capabilities of an ammeter (measures current), voltmeter (measures potential difference, or voltage, between two points) and an ohmmeter (measures resistance) in one instrument to take measurements (current, voltage and resistance) from circuits. . Multimeters are available at Radio Shack (or other electronics store), ranging from $15-$100.

Activity Scaling (Return to Contents)

  • For lower grades, use the math worksheets as a challenge activity or complete them together, as a class.

Owner (Return to Contents)

Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder

Contributors

Xochitl Zamora Thompson, Sabre Duren, Joe Friedrichsen, Daria Kotys-Schwartz, Malinda Schaefer Zarske, Denise Carlson

Copyright

© 2004 by Regents of the University of Colorado.
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0226322. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.

Last Modified: April 27, 2006
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