Labs from Chicago, Summer 1993:
Dr. Jim Sweitzer
Calibrating the Sun's Light.
Labs written for the CARA Space Explorers, Summer 1994
This is a Teacher's guide.
Objectives of lab:
- Establish a way to compare light intensities from the Sun and
a "home-made" light source.
- Measure the luminosity of the portable light source as a
function of solar luminosity. (This assumes they will know the
distance to the Sun.)
- Begin to attack the problem of filters and measuring only a
certain band of the Sun's spectrum.
- Sun (If it's a cloudy day, we'll have to set up an ersatz Sun in
the lab.) Only one needed.
- Flashlights(with fresh batteries), heavy aluminum foil, tape
and lengths of fiber optics. Will probably also need scissors, if foil
isn't pre-cut. We'll need enough materials for one device per two
- Meter sticks, projection surface and things to cast shadows.
- Filters: The regular V filter for astronomical investigations &
other miscellaneous ones. It would be great if I could get a large
sheet of one (about a foot or more square).
Important Disclaimers and
- Introduce students to what we'll be doing and build a bridge
with what they've learned before. Have them first try using their
flashlights alone on the screen described below.
- Build fiber-optic light sources. This will be done by cutting
the foil into pie shapes that can be rolled into cones. The fiber will be
taped at the tip of the cone. The base of the cone will fit over the
business end of the flashlight.
- Try them inside with a setup that consists of a light bulb
with its light directed on a sheet of paper. We'll need some sort of
baffle to give a nearby shadow. Illuminating the shadow with their
fiber optic source, each team measures the distance between the
fiber and the shadow portion of the projection screen.
- Go outside (this could also mean working on the balcony
outside of the physics lounge on the second floor) and use the fiber-
optic light sources to illuminate shadows. Measure the distance
between the light source and the fiber optic.
- Inside compute the intensity of the fiber source relative to
the Sun using the inverse-square law.
- Briefly discuss the results and try to understand the
variables as well as the consistency and accuracy of this method.
- Go out one more time and repeat the experiment using the V
- Discuss final results and christen the source we'll use at
- Conclude by bridging to Yerkes activities. At some point in
this activity it will be important to explain why we are using a fiber
"point" source and not just the flashlight itself.
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