What Can You Learn from a Holiday Light and a Glass Cup?

Vicki Cobb
The “Julia Child” of kids’ hands-on science

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A land surveyor sends a heliograph to his partner more than 100 years ago. He must have been fluent in Morse Code

     How do you know it’s the holiday season?  There are lights everywhere sending that message.   But that’s not the only kind of message light can send.  A little more than 100 years ago when a telegraph began to become popular, people sent wireless messages called heliographs.  They were made of flashes of light in Morse code (the same pattern of short and long as used in telegraphs) by reflecting the sun’s rays with a mirror.  When the mirror was at a particular angle to the sun, it reflected a flash of bright light to observer miles away.  

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Note where the red light from the bulb emerges on the opposite side. Some internally reflected light is emerging from a ridge in the glass. Photo by Alexandra Siy

     Maybe there’s another way to send light.  Put a holiday light on one rim of a heavy glass measuring cup or dish.  See where the light emerges on the rim on the opposite side.   Move the light back and forth and watch what happens on the other side.  The light travels down the side, and bends to go across the bottom and up the other side, but if you look at the cup sideways you can’t see the beam.  Light stays inside the glass as it travels from rim to rim.

     Could we make something like a wire from glass that can transmit light?  Absolutely! An optical fiber is a flexible, transparent fiber made of glass or plastic that acts as a wire for light.  Imagine a beam of light entering a fiber at exactly the right angle to bounce off the inside wall of the fiber where it meets the air.  It is then reflected at exactly the same angle to bounce off the opposite wall making a zig-zag path until it reaches the end of the fiber. This internally reflected light stays inside the glass fiber as it travels at the speed of light. 

     HUGE quantities of all kinds of information—words, pictures, music, and videos—can now be sent through optical fibers, much more than through wires.  A modern network with copper wiring can handle about 3,000 telephone calls at the same time, while a similar system using fiber optics can carry more than 30,000!

     So when you hit “send,” know that your holiday message is a blinking beam of light, bouncing off the inside walls of a glass fiber on its speedy journey to friends and family.  How ‘bout that!

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Fiber optics can be made into holiday decorations. Note the bright light emerging from the ends of the fibers.

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Want to know more about optics?  Have a look at Vicki Cobb's book Light Action! She co-authored it with her son, Josh, who is an optical engineer and her other son, Theo, drew the pictures.  It's full of experiments that let you use optics to:
-Bend light around corners
- Stop time with a pair of sunglasses
- Capture light on a silver tray
- Magnify pictures with an ice cube
- Pour light into your palm
- Project a big-screen image from your small TV
- Fool a doorbell with a bike reflector!
For more information, go  here. 

Vicki is a member of iNK's Authors on Call and is available for classroom programs through Field Trip Zoom,  a terrific technology that requires only a computer, wifi, and a webcam.  Click here to find out more.

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MLA 8 Citation
Cobb, Vicki. "What Can You Learn from a Holiday Light and a Glass Cup?" Nonfiction Minute, iNK Think Tank, 14 Dec. 2017,  www.nonfictionminute.org/ What-Can-You-Learn-from-a-Holiday-Light-and-a-Glass-Cup.