Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography

PLEASE REQUEST DEMOS WELL IN ADVANCE

Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

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Geometrical Optics: Speed of Light; 1/r² Demonstrator; video - Ray Optics Kit; Confocal Mirrors; Concave Mirror; video - Light The Match; Disappearing Beaker; String Model of Refraction; Total Internal Reflection; Steal the Light; Light Pipe and Fiber Optics; Water Light Pipe; Thin Lenses with Objects
Diffraction
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The Eye

Speed of Light

Purpose:

A direct measurement of the speed of light in air by measurement of the time delay of a 10ns pulse which travels two different paths after being split.

Procedure:

With the help of a student, measure the distance between the two mirrors as accurately as possible. The mirrors will be aligned before class and if disturbed, re-alignment can take several minutes depending on familiarity with the equipment. Make sure the oscilloscope is being projected for the class to see and plug in the laser diode. The first mirror intersects the beam at its edge and so only reflects part of the beam back to the detector. The rest of the beam travels to the end of the bench and back to the same detector. Two pulses should appear on the display. A somewhat careful measurement of the time between pulses and the distance between the mirrors can lead to a calculated value of the speed of light within 3% of the actual value.

Hints:

Set the trigger holdoff to greater than the time between first and second pulse ie. 50 to 100ns.
Note that the laser source puts out 10ns pulses at the rate of 885kHz (1.13us between source pulses).

Equipment:

Oscilloscope
Tape Measure