Elenco Fiber Optics Voice Data Kit - Manual (Page 7)

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Optical fibers can transfer light through bends and curves
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True optical fibers can do more than transfer light from one end to the other through an
established path. In this activity we will bend the plastic rod to further demonstrate the rod's "light-
guiding" properties and how light can be "persuaded" to travel around bends and curves.
M M M M aaa a tttt eeee rrrr iiii aaa a llll ssss N N N N eeee eeee dddd eeee dddd ::::
Penlight with batteries
Black rubber penlight boot
3 mm (1/8 inch) diameter plastic rod, 30 cm (12 inches) long
Alcohol lamp, Bunsen burner or propane torch*
Pair of cotton gloves or cloth pads*
* Not contained in this kit.
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• Place your heat source on a firm flat surface. Light the fuel with a match and adjust the flame
until it burns steadily.
• Remove the plastic rod from the rubber boot. Using gloves or cloth pads, carefully grip each end
of the rod. Hold the center of the rod above the flame and heat a central area about 10 cm (4
inches) long. Rotate the rod so it heats evenly.
• When the center of the rod is flexible, remove it from the heat and quickly bend the rod into a
"U-shape" as shown in the illustration here. Turn the heat
source off and allow the rod to cool for at least five minutes.
• Insert one end of the curved rod into the hole in the rubber
boot on the penlight, and turn the penlight on. Observe the
light coming out the other end of the rod. Is the light's
intensity the same, greater, or less than before you bent the
rod? Turn the penlight off.
R R R R EEEE SSSS UU U U LLLL TTTT SSSS ::::
The light should travel from end to end in the "U-shaped" rod
just as well as in Experiment 1. Any decrease in light intensity
should be very slight.
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Light traveling inside the straight acrylic rod actually
"bounced" back and forth off the inner walls of the rod many times,
at very small angles. Even when the acrylic rod is bent, light strikes
the interior walls of the rod at pretty much the same angles. Light continues to travel from one end to
the other just as it did when the rod was straight.
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Egyptian geographer Ptolemy (AD 90-168) probably devised the first "laws" or scientific theories
that predicted how light would interact with matter. Sometimes his theories worked; sometimes they
didn't. It was Willebrord Snell (1580-1626), a Dutch
mathematician and astronomer, who refined these
principles to what we know and use today in predicting
how light rays will act when they encounter optical
materials like our acrylic rod.
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