The learning activities in this Lesson will help students prepare to complete the GE Lighting Auditor for their school or home as they learn about the lives of Thomas Edison and Lewis Latimer, both of whom contributed to the improvement and practicality of the light bulb.

This Lesson comprises three learning activities.

Thomas Edison's Biography is a Read About that offers an historical view of Edison's life.

Lewis Latimer's Biography is a Read About that describes the life of one of the most influential of Edison's Pioneers, who was a brilliant inventor in his own right.

In Designing a Filament, an Experiment, students recreate one of the investigations that led Edison and Latimer to perfect the tungsten filament.

• the historical significance of Thomas Edison and his inventions.
• the historical significance of Lewis Latimer and his inventions.
• the process of inventing.
• how a light bulb works and how it is constructed.

The chart below suggests options for incorporating the activities into your schedule.

In 1879, Thomas Edison finally achieved a working light bulb after many hundreds of failures. His greatest challenge was to find a material for the filament that could remain heated for days before burning up. Edison realized early on that, regardless of which material worked best, the filament must be contained in a vacuum.

In this next experiment, you will recreate the efforts of Thomas Edison to develop the incandescent light bulb. Before you begin, you should know that you will likely not have the kind of success that Edison achieved, but knowing that should better prepare you for the challenge of building a working light bulb!

After you have developed the techniques to construct a basic working light bulb, you are then going to be challenged to test a variety of materials for the filament, just as was Edison over the months and years before 1879.

In this activity, you will be creating a partial vacuum in a jar. The better the vacuum, the longer the filament will glow before burning out.

• A 1 quart jar with tight fitting lid (such as a mayonnaise, peanut butter, or canning jar)
• Masking tape
• Scissors
• A small nail and hammer
• Small gauge electrical wire (about 1 meter)
• Lamp wire
• One 6-volt battery
• Birthday candles
• Small amount of modeling clay
• Stop watch (or a clock with a second hand)

Use the a nail to punch 2 small holes in the lid of the jar, about 5 cm apart. Strip off the insulation from the ends of each wire using a pair of scissors. Run one end of each wire through the lid of the jar, so that they extend to about the middle of jar when the lid is on. Use tape to tightly plug the holes in the jar lid. Attach the end of one wire to one terminal on the 6-volt battery.

Now you need to add the filament. Remove a single strand of wire from lamp wire, about 4 cm long. Wind the wire around the nail to make a coil, noting the number of coils. Then carefully remove the coil from the nail and connect it to the two ends of the wire attached to the lid (this will take some skill). Now, you are ready to test your first light bulb.

For this part of the test, it is best to have one person work the bulb and the other work the stopwatch or wristwatch. The timekeeper should give a countdown (much like a rocket launch), at which time the light bulb operator touches the unattached wire to the remaining battery terminal. Keep contact until the filament burns out, or until 15 seconds have passed. (If your light bulb is too successful, you will drain the battery). How bright did the filament glow? For a more exciting effect, dim the lights in the room for each test.

If the filament glows for more than 15 seconds, run the experiment again, but with progressively shorter filaments. Keep the number of coils in each filament constant. Do you think the shorter filaments will burn shorter or longer? Record the length of each filament and the duration the filament burned on a datasheet. You can prepare a graph showing filament length on the x-axis and duration of the filament on the y-axis. If the longer filaments burn longer, why not make light bulbs with very long filaments? If you are a good observer, you may have the answer. Although longer filaments last longer, they do not glow nearly as brightly. All the energy going into the bulb ends up as heat rather than as light. Can you think of devices in your home that use coils to produce heat rather than light?

In this experiment, you will use a lit candle as a means of creating a vacuum in the jar. How do you think a vacuum will affect the longevity of your filament? Using the data collected in the first experiment, select a filament length that burned for about 5 seconds. Prepare at least 5 of these filaments for use later.

Use the modeling clay to make a base for the birthday candle and place the candle in the jar. Place it off to the side so as not to interfere with the filament. Now, light the candle and quickly, tightly screw the lid on the jar. When the candle goes out, a partial vacuum is created. (How?) Have the timekeeper start keeping time when the bulb is turned on. How long did the filament burn now? Record your results. Repeat the experiment several more times, making certain to keep the shape and the length of each filament constant. How has a vacuum affected the duration of the filament's burn? Now you know why a light bulb makes that loud pop when you drop one!

Now that you have perfected the partial vacuum light bulb, you can try different filaments. Before you begin, think about the two desirable qualities in a light bulb. As you learned earlier, the duration of the filament isn't the only quality sought after; the amount of light produced is also critical. Using the procedures developed above, try other materials as filaments. Suggestions include steel wool fibers (you can wind them together to make different thicknesses of filament), thin craft wire, and thinner pieces of copper wire. You can even collect the actual filament from a real light bulb by placing the bulb in a plastic bag, placing the bag under a heavy cloth, then striking the bulb with a hammer. Carefully remove the filament from the bag, taking great care not to cut yourself. The filament and the wire connectors can be cut from the base of the bulb and attached to the wires in your light bulb. How does the real thing compare with your own homemade filaments? The fact is, even the real filament (made of a metal called tungsten) will not last that long without a good vacuum. Record all of your findings as you test each filament.

You might want to prepare a report of your findings to your classmates or prepare a presentation board showing your setup and the results from your tests as graphs or tables. Be sure to include your materials and methods and your conclusions. How good were you at building the better light bulb?