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Unformatted text preview: am into the detector hole, and ensure that the tiny beam is directly on
the tiny detector diode. This will take many adjustments and some patience. Use the scissor jack to elevate
the laser and/or detector boxes to the proper height. (The alignment is achieved more easily if the two lab
partners work together!)
4. Use the skills you have learned in Part B above to measure the time values for two different laserdetector distances (one really close, one as far as possible on your lab table). When you have the distances
recorded, and their corresponding time values, calculate the speed of light in air. (HINT: it is not necessary
to know the cable length, how much time the signal spends in the cable, nor the delay time of the amplifier
D. Speed of light in transparent plastic
Measure how long it takes the pulse to leave the laser and arrive at the diode detector while traversing an
1. This is a particularly challenging task, since you will not only be aligning the laser beam with the
detector – you will also have to contend with a clear plastic rod in between them which will potentially be
bouncing the beam all over the place!
2. Measure the length of the acrylic rod and record it. DO NOT SCRATCH THE ENDS OF THE
RELATIVELY SOFT ACRYLIC ROD; THIS COULD ADVERSELY AFFECT THE RESULTS OF
THE EXPERIMENT. Position the laser and detector such that the laser points into one end of the rod
(almost touching), shoots the beam through its length, and comes out the other end directly into the detector
(also almost touching). You will have to take pains such that the center (axis) of the tube and the beam
are co-linear; this can best be accomplished by positioning both laser and detector at the center of the
ends of rod. (TIP: Position the laser and detector about a rod's length from each other at about the same
height (using the scissor jack under one of them), about the length of the rod apart. Then, cradling the rod
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This document was uploaded on 12/27/2012.
- Summer '09