This unit consists of an interlinked series of 6 multi-part
experiments using inexpensive materials such as lights bulbs,
heater wire, and an ohmmeter. In the first experiment, students
discover that Ohm's law doesn't appear to be valid for the filament
resistance of the light bulb. They then develop the understanding
that this arises from the change in filament resistance with
temperature. This experiment connects commonly used technology
- the light bulb - with the mathematics of Ohm's law as well
as with the dependence of the electrical properties of materials
on their composition, length, and diameter. In a subsequent series
of experiments, students investigate a 3-way bulb, a 3-way switch,
and then a 3-way bulb in a 3-way switch socket. They develop
the understanding - using observation, logical reasoning, and
mathematical modeling - that a 3-way bulb consists of 2 filaments
which are connected in parallel at the highest wattage setting.
In the third experiment, students design a light bulb and describe
the fabrication steps necessary to construct it; students are
given some basic engineering information before attempting the
experiment. They then dissect a light bulb and determine how
close their earlier design resembles a real bulb. Finally, they
must design and construct a light bulb that operates in air using
materials that are similar to those found in a light bulb, but
are oxidation resistant. These materials are available as a kit fromthe General Atomics Sciences Education Foundation as GASEF #013.
GASEF #013 contains 10 20-cm long pieces of 0.003 inch diameter
Kanthal AF wire, 2 20-cm long pieces of 0.010 inch diameter Kanthal
AF wire, and 2 20-cm long pieces of 0.020 inch diameter copper
wire.
This unit also consists of an extensive introduction with background
information into advanced topics such as oxidation resistant
materials, blackbody radiation, filament materials, filament
environments, and a microscopic view of incandescence. Also explored
are a brief history of the development of the light bulb and
Edison's critical role in the methodology of experimental science,
which set the subsequent standard for industrial research. A
teacher's guide to all experiments, related mathematical problem
sets, and solutions is included the module. This unit provides
a natural tie to studies in economics and US history that involve
the electrification of society, the industrial revolution, the
rivalry between AC and DC distribution systems, and the growth
of industrial laboratories. Students require a previous introduction
to Ohm's Law and series and parallel circuits before beginning
this unit. These experiments are aimed at grades 7-12, but would
also be appropriate for an introductory university physics or
materials science course.
This unit relates to the NSES physical science
content standards in grades 5-8: "Energy is a property of many substances and is
associated with heat, light, electricity ... Energy is transferred
in many ways. Electrical circuits provide a means of transferring
electrical energy when heat. light, sound, and chemical changes
are produced;" and in grades 9-12: "Energy can be transferred
... in many ways. In some materials, such as metals, electrons
flow easily, whereas in insulating material they can hardly flow
at all."
Download Entire Unit (1.1MB PDF)
This unit was developed by Dr.
Lawrence D. Woolf