Hands-on Activity: Light Your Way: Design-Build a Series Circuit Flashlight

Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

Summary

During a power failure, or when we go outside at night, we grab a flashlight so we can find our way. What happens inside a flashlight that makes the bulb light up? Why do we need a switch to turn on a flashlight? Have you ever noticed that for the flashlight to work you must orient the batteries a certain way as you insert them into the casing? Many people do not know that a flashlight is a simple series circuit. In this hands-on activity, students build this everyday household item and design their own operating series circuit flashlights.
This engineering curriculum meets Next Generation Science Standards (NGSS).

A glowing flashlight turned on in the dark.
Students explore how a flashlight works
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Engineering Connection

When engineers design electrical equipment, they figure out the optimum circuitry design for the situation, whether it is the installation of solar panels, design of electric cars, behavior of traffic signals, hair dryer on/off switch, turn indicator lights on a vehicle or even a simple flashlight. They decide between creating a parallel or series circuit, or they often create a complex circuit system composed of both types.

Learning Objectives

After this activity, students should be able to:

  • Design and construct a working portable flashlight.
  • Define, recognize and assemble series circuits.
  • Explain the path of electrical charge through their circuit.
  • Describe the engineering process behind designing a flashlight.

More Curriculum Like This

Circuits: One Path for Electricity

Students learn that charge movement through a circuit depends on the resistance and arrangement of the circuit components. In one associated hands-on activity, students build and investigate the characteristics of series circuits. In another activity, students design and build flashlights.

Bulbs & Batteries in a Row

During this activity, students build a simple series circuit and discover the properties associated with series circuits.

Elementary Activity
Electrons on the Move

Students learn about current electricity and necessary conditions for the existence of an electric current. Students construct a simple electric circuit and a galvanic cell to help them understand voltage, current and resistance.

Elementary Lesson
Parallel Circuitry & Ohm’s Law: Many Paths for Electricity

Students explore the composition and practical application of parallel circuitry, compared to series circuitry. Students design and build parallel circuits and investigate their characteristics, and apply Ohm's law.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Show that electricity in circuits requires a complete loop through which current can pass (Grade 4) Details... View more aligned curriculum... Do you agree with this alignment?
  • Describe the energy transformation that takes place in electrical circuits where light, heat, sound, and magnetic effects are produced (Grade 4) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

Each group needs:

  • 2 D-cell batteries (If each student brings in 2 D-cell batteries, then they can take their homemade flashlights home with them. If you do this, make sure to have enough of the other supplies to make one flashlight per student, not per group.)
  • 5 pieces of insulated copper wire (various lengths) (available at hardware stores)
  • 1 #40 bulb (available at hardware stores)
  • 1 bulb holder (available at hardware stores)
  • 1 cardboard paper towel or wrapping paper tube
  • Light Your Way Worksheets, one per student

For the entire class to share:

  • reflective material, such as aluminum foil, small pie tins, foil muffin cups, etc.
  • thumb tacks
  • rubber bands
  • masking tape
  • wire strippers or medium-grade sandpaper (to remove insulation from wire ends)
  • wire cutters
  • scissors

Optional materials for this design project:

  • thin flat strips of wood or plastic
  • switch (available at Radio Shack or other electronics stores), or a variety of materials to make switches: paper clips, aluminum foil, nails, coins, insulated wire (possibly of varying gauges), keys, etc.
  • thumb tacks

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

Have you ever heard a bell or buzzer from a ringing building alarm? (Some will answer yes.) Let's brainstorm: How do you think the building knows to set off an alarm when an intruder tries to open a door or window? (Give students some time to think of some ideas. Possible answers: The building is really smart, or the alarm circuit is broken causing the bell to sound.) Electrical engineers design the wiring of an alarm system to be an "in series" circuit. The doors and windows of the building act as a switch for the alarm circuit. The alarm circuit is a closed circuit when the alarm is on and the windows and doors are closed. However, when someone tries to open a door or window (without turning off the alarm first), the alarm circuit becomes "open" and the building is, in essence, telling the alarm to sound.....ding, ding, ding!

Alarm systems are not the only items with an in series circuit. Batteries can also be connected in series, which provides more voltage to a device. For example, if we connect three AA batteries "in series," it provides more voltage than a single AA battery. When engineers design a flashlight, they determine if the batteries should be connected "in series" or "in parallel."

During today's activity, just like engineers, we will design our own flashlights and determine if the batteries in our flashlight will be connected "in series" or "in parallel."

Procedure

Background — Flashlights

The first flashlight was invented in 1896, and made possible by the invention of the D-cell battery in that same year. Prior to 1896, the only battery that could be used for portable lighting was too heavy to be practical. These new devices were called "flash lights" because they provided a brief flash of light when the user pushed a switch — unlike the steady light beam produced by today's flashlights.

Over time, the parts of a flashlight have not changed much (see Figure 1). Batteries are connected to a bulb in a basic series circuit containing a switch. A metal reflector placed behind the bulb increases the light output. A protective lens cap covers the bulb and reflector. A casing, often tubular in shape, contains the batteries, bulb, spring, wires and reflector, and connects to the lens cap. The switch is held in place on the outside of the casing. The flashlight that students build in this activity has all these parts except a lens cap and the spring.

A drawing show a cylindrical tube containing: two dry cell batteries connected in series, a spring contacting the negative terminal of one battery, a light bulb touching the positive terminal of the second battery, a reflector at the base of a light bulb, and protective glass at the end of the flashlight next to the bulb. Outside the flashlight casing is a switch.
Figure 1. Cross-section of a flashlight, showing its component parts.
copyright
Copyright © 2003 Joe Friedrichsen, ITL Program, College of Engineering, University of Colorado Boulder

Before the Activity

  • Collect leftover pieces of insulated wire (various lengths) from previous electricity activities.
  • Assemble all the materials.
  • Note: If you are using pre-made switches, you will not need to assemble any switch materials.

A schematic of a simple flashlight circuit includes two batteries (connected in series), a light bulb, wire and a switch. One light bulb and wire is connected to the positive terminal of the battery. The other side of the wire is connected to the switch, which is used to turn the flashlight on and off. The second wire is connected to the other side of the switch and the negative terminal of the second battery.
Figure 2. The basic circuit for constructing a flashlight.
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With the Students

  1. Open-ended design: Have students form into teams of four. Inform them that the goal of this activity is for teams to design and construct a working flashlight using only the provided materials. The flashlight must turn on and off using a switch. Also, all of the wiring and batteries must be contained within the paper towel tubes. All team members must participate in both the design and building phases.
  2. Discuss the qualities of a good flashlight with the students. (Possible features: On/off switch, reliable switch, easy-to-use switch, easy to carry, small size, bright beam of light, lasts a long time, does not break.) Hand out the Light Your Way Worksheet, and have students fill out the corresponding question on the worksheet.
  3. As a class, have students draw a flashlight on the board. Individual students should contribute one part to the drawing. (Parts include: Case, spring, bulb, switch, protective glass/plastic, reflector, batteries.) Have other students describe the function of each part of the flashlight that has been drawn. (For functions, see the Light Your Way Worksheet Answers.) Have each student answer the corresponding question on the worksheet.
  4. Show students the materials available to construct their flashlight. Let teams brainstorm the design of their flashlight, determining which materials they will use for each part. To aid the brainstorming process, show students the circuit diagram for a typical flashlight (Figure 2) as a printout or by drawing it on the board. Have students document their materials plan on the worksheet (question #3).
  5. Have students draw a circuit diagram for their flashlight on the worksheet.
  6. Have students write out the steps they are going to take to build their flashlight. Once you have looked at (and approved) a team's design, have the students gather their materials.
  7. Allow time for each team to construct their flashlight design.
  8. Test each team's flashlight. To be considered reliable, it should be able to light up three times in a row. If a team's flashlight does not work, have them compare the flashlight circuit diagram (Figure 2) to their team's flashlight circuit diagram. On the worksheet, have students write up any design changes or fabrication improvements they need to make. If time permits, have them implement their changes so the flashlight works.

Three photos (1) Two batteries are connected in series with masking tape, with the positive terminal of one battery touching the negative terminal of the second battery, and an insulated wire taped to the negative terminal of the second battery. (2) A side view of the flashlight shows the batteries and wires encased in a paper towel tube, a switch on the outside of the tube and a folded square of aluminum foil cupped behind the bulb as a reflector. The switch is made from a paper clip, a thumbtack and masking tape. Insulated wires from each side of the switch run into the ends of the paper towel tube and are taped flat onto the tube. (3) The front view of the flashlight, with the bulb lit.
Figure 3. An example flashlight design.
copyright
Copyright © 2003 Joe Friedrichsen, ITL Program, College of Engineering, University of Colorado Boulder

Attachments

Safety Issues

  • Caution students not to play with the insulated wire; they may poke or cut themselves or others.
  • Caution students not to hold the insulated wire on the D-cell battery with their fingers for extended periods of time. The stripped ends of the wire heat up when held on the battery terminals.

Troubleshooting Tips

Slice small cardboard tubes down the middle to accommodate the D-cell batteries.

A paperclip may be used to hold the light bulb in place.

Have students make sure all of their connections are reliable, so when they move the flashlight the connections do not come loose.

Ideally, all the wires used in the flashlight should be contained within the paper towel tube — no wires should be hanging out. If students have problems making the switch inside the tube, have them set up their switch externally, as in Figure 3.

Assessment

Pre-Activity Assessment

Brainstorming: Have the students engage in open discussion to list on the board the qualities of a good flashlight. Remind students that no idea or suggestion is "silly." All ideas should be respectfully heard. Encourage wild ideas and discourage criticism of ideas.

Drawing: As a class, have students draw a flashlight on the board. Individual students should contribute one part to the drawing. (Parts include: Case, spring, bulb, switch, protective glass/plastic, reflector, batteries.) Have other students describe the function of each part of the flashlight that has been drawn. (For functions, see the Light Your Way Worksheet Answers.) Have each student answer the corresponding question on the Light Your Way Worksheet.

Activity Embedded Assessment

Worksheet: Have the students complete the Light Your Way Worksheet; review their answers to gauge their mastery of the subject.

Use the Fraction Circuit Worksheet to learn about circuit diagrams and practice adding fractions!

Drawing: Have students draw a circuit diagram of their flashlight on the Light Your Way Worksheet.

Brainstorming: In their teams, have the students engage in open discussion to determine the design of their flashlight. They should decide which materials they will use for each part. All ideas should be respectfully heard. Encourage wild ideas and discourage criticism of ideas. Have each student answer the corresponding question on the Light Your Way Worksheet.

Procedure Practice: Using the Light Your Way Worksheet, have students list the steps they will take to design and build their flashlight.

Re-Design Practice: Have the students list any design or fabrication changes they would make to their flashlight on the Light Your Way Worksheet.

Post-Activity Assessment

Drawing: Using the Light Your Way Worksheet, have students complete the last item on the worksheet by drawing their team's flashlight and labeling all the parts.

Sales Pitch! Have the students pretend to be salespeople who are trying to sell their flashlight to a manufacturer or a consumer. Have student teams create a persuasive poster or flyer, as well as a 10-minute sales pitch of their flashlight design for presentation at the next class. Have them incorporate into their sales pitch their series circuit diagram, the parts and features of the flashlight and how it works.

Activity Extensions

Portable flashlights can be powered by means other than batteries. Have students conduct Internet research on solar-powered flashlights, "shake" flashlights and "crank" flashlights. Ask students to discuss the environmental and economic implications of using these types of flashlights.

Activity Scaling

  • For lower grades, provide completed flashlight examples and a drawing of the electrical circuit (as a printout or on the board) for students to examine. This helps them during the brainstorming process when they determine what materials to use to construct a flashlight. Complete the circuit diagram on the Light Your Way Worksheet together, as a class.
  • For upper grades, you may not need to provide a drawing of the flashlight's electrical circuit for students to examine during the brainstorming process when they determine what materials to use to construct their team's flashlight.

References

Activity adapted from: Make a Flashlight, Rough Science, PBS. Accessed April 29, 2004. http://www.pbs.org/weta/roughscience/discover/powerplant.html#flashlight

Contributors

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

Copyright

© 2004 by Regents of the University of Colorado

Supporting Program

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

Acknowledgements

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation (GK-12 grant no. 0338326). 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: February 22, 2018

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