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Developer:
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Shirley Hall
Overbrook Educational Center
School District of Philadelphia
Philadelphia, PA
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Dr. Charles Jones
Rohm and Haas Company
Spring House, PA
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Grade Levels:
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4 through 8
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Discipline:
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Electricity/Physical Science
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Goals:
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Students will gain a better understanding of how light is produced in an electric incandescent bulb.
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Specific Objectives:
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Students will construct a wire filament similar to that found in an incandescent bulb.
Students will connect the filament to an electrical source that will make the filament glow.
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Background:
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The invention of the electric light bulb was one of the greatest inventions of all time. It is taken for granted that, with a flick of a switch, light will be cast into the area that we wish to have illuminated.
The incandescent bulbs that are commonly used in households today consist of three basic parts: the base, the bulb and the filament. The base connects the bulb to an electrical circuit, such as a lamp. The bulb keeps air away from the filament so that it will not burn too quickly. In fact, most bulbs are filled with a mixture of gases to help lengthen the life of the filament. The filament is a coil of thin wire. When electricity flows through the wire, it heats up to a temperature of 2480 degrees C or more and glows brightly. Most filaments are made of tungsten, a strong metal that can withstand high temperatures without melting.
In this activity, students will connect a thin coiled wire to an electrical source. This wire will glow red for a short period of time.
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Materials:
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2 pieces of insulated wire
glass jar with lid
1 piece of very thin copper wire
masking tape
6V lantern battery or 9 V battery
nail
hammer
sandpaper
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Questions:
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- What did you observe as the electricity started to flow through the coiled wire?
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Why did the wire glow red instead of white as in a typical light bulb?
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3. Why was your filament placed in a glass jar?
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4. How did the coiled wire look at the end of the experiment?
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5. Find out who is credited with the invention of the first electric light bulb. What other commonly used objects did he invent?
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References:
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Stein, Sara, The Science Book, 1979, Workman Publishing, New York
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Procedure:
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Remove the lid from the jar. Use a nail and a hammer to put two small holes in the lid of the jar. NOTE: If the lids are plastic, a nail may be heated over a flame and pushed through the lid to make the holes and keep the plastic from cracking.
Strip the insulation from both ends of the insulated wire. Thread one end of each piece of insulated wire through each of the small holes. (The wire should extend about halfway into the jar once the lid is screwed back on.) Tape the wires into position on top of the lid so that they will not shift.
If necessary, use the sandpaper to strip off any insulation that may be painted on the thin copper wire. Wrap the thin copper around one end of the insulated wire to make a tight coil of wire. Slide the coil off the end of the insulated wire.
Attach the coil of wire to the insulated wire that will extend into the jar. Screw on the lid with coiled wire attached carefully inside the jar. Attach the free ends of the insulated wire to the battery terminals. The filament inside the jar will glow red for a short period of time. Detach the wires from the battery once the filament stops glowing. CAUTION: Let the coil cool before disconnecting the wire inside the jar.
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Extension Activities:
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Connect the filament wire to the insulated wire without coiling it. Are the results the same? Why or why not?
Make the filaments into larger coils. What happens?
Experiment with ways to increase the life of your filament. What variables could you change?
How can a switch be attached to your light bulb?
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