Stroboscopic Photography Timed with an Oscilloscope
Although software is available to simulate a bouncing ball and a "g" measurement, the oscilloscope, a stroboscope and a camera can be used to measure the acceleration due to gravity. The time interval between successive images of the bouncing ball can be set to the frequency of alternating house current. In this experiment, the oscilloscope displays the Lissajous pattern which tunes the stroboscope's frequency to the house current's frequency. At that instant, the picture is taken. While commercial stroboscopes are available, this author used an overhead projector to obtain a bright enough source of light for typical black and white film and an old light meter to convert the pulses of light into pulses of electricity. For another source on stroboscopic photography: The Edgerton Explorit Center provides hands-on scientific learning for all ages. Explore Dr. Edgerton's work with photography and tour the Center online.
In this wiring diagram, the author set the oscilloscope's horizontal
sweep control on "Line" which disables the horizontal time sweep
and sets the horizontal sweep frequency at 60 Hertz.
This view shows the oscilloscope hooked up to the light meter and
the overhead projector in place with the mechanical stroboscope's
motor controlled by a variable speed control.
At the instant the Lissajous Pattern stops rotating, the stroboscope's
frequency is "tuned" to the frequency of house current,
and the camera captures the picture
(the actual strobe frequency is 120 Hertz using 60 Hertz, A.C.).
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Physics and Chemistry Departments
Carson City-Crystal High School
Carson City, Michigan 48811
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