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A Glass Thread That Carries Light Around Corners

5th grade nonfiction passage about light inside optical fibers: 213 words, six questions, an answer key and vocabulary.

5th grade nonfiction light inside optical fibers 213 words

A Glass Thread That Carries Light Around Corners

Light usually travels in straight lines, so it seems strange that it could follow a curve. Yet very thin threads of glass can carry light around bends, even over long distances. These threads are called optical fibers.

How do they work? Each fiber has a center, or core, made of very clear glass. Around the core is a layer of a different kind of glass. When light moves down the core and strikes the edge of that outer layer at a shallow angle, it does not escape. Instead, it bounces back inside, a little like a ball bouncing off the walls of a hallway. The light zigzags along the fiber again and again until it reaches the far end.

Why is this useful? A flash of light can carry a message. Light that blinks on and off very quickly can stand for letters, pictures, and sounds. Signals in glass fibers can carry a huge amount of information and lose very little along the way. Many telephone and internet lines now use fibers for this reason.

Some bundles of fibers carry plain light instead. They let people shine a beam into narrow places and see what is inside. In both jobs, a hair-thin strand of glass guides light wherever it needs to go.

Questions

  1. What are the thin glass threads called? in the text

  2. What is the core of a fiber made of? in the text

  3. What happens when light hits the edge of the outer layer at a shallow angle? in the text

  4. Why does the passage compare light to a ball in a hallway? think about it

  5. What can quick blinks of light stand for? in the text

  6. Why are fibers a good choice for internet lines? think about it

Words to know

optical
having to do with light and seeing
core
the center part of something
shallow
not steep, a very slight slant
zigzag
to move in sharp turns from side to side
bundle
a group of things tied or held together
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 205 words · Flesch-Kincaid grade 3.3

Light moves in straight lines. So it seems odd that light could follow a curve. But very thin threads of glass can carry light around bends. They can do it over long distances. These threads are called optical fibers.

How do they work? Each fiber has a center, called the core. The core is made of very clear glass. Around the core is a layer of a different glass. Light moves down the core and hits the edge of the outer layer at a shallow angle. It does not escape. It bounces back inside, like a ball bouncing off the walls of a hallway. The light zigzags along the fiber until it reaches the far end.

Why is this useful? A flash of light can carry a message. Light that blinks on and off very fast can stand for letters, pictures and sounds. Glass fibers can carry a lot of information and lose very little. Many phone and internet lines use fibers for this reason.

Some bundles of fibers carry plain light. They let people shine a beam into narrow places and see what is inside. In both jobs, a strand of glass as thin as a hair guides light where it needs to go.

▲ This passage · 213 words · Flesch-Kincaid grade 5.3

Light usually travels in straight lines, so it seems strange that it could follow a curve. Yet very thin threads of glass can carry light around bends, even over long distances. These threads are called optical fibers.

How do they work? Each fiber has a center, or core, made of very clear glass. Around the core is a layer of a different kind of glass. When light moves down the core and strikes the edge of that outer layer at a shallow angle, it does not escape. Instead, it bounces back inside, a little like a ball bouncing off the walls of a hallway. The light zigzags along the fiber again and again until it reaches the far end.

Why is this useful? A flash of light can carry a message. Light that blinks on and off very quickly can stand for letters, pictures, and sounds. Signals in glass fibers can carry a huge amount of information and lose very little along the way. Many telephone and internet lines now use fibers for this reason.

Some bundles of fibers carry plain light instead. They let people shine a beam into narrow places and see what is inside. In both jobs, a hair-thin strand of glass guides light wherever it needs to go.

■ Harder · 232 words · Flesch-Kincaid grade 9

Light ordinarily travels in straight lines, so the notion that it could follow a curve seems almost absurd. Nevertheless, extremely thin threads of glass can guide light around bends, even across enormous distances. These threads are known as optical fibers.

The mechanism is surprisingly simple. Each fiber has a center, or core, made of exceptionally clear glass, and surrounding the core is a layer of a different kind of glass. When light moves along the core and strikes the boundary of that outer layer at a shallow angle, it cannot escape. Instead, it reflects back into the core, much like a ball rebounding off the walls of a long hallway. The light zigzags along the fiber over and over until it arrives at the far end.

The usefulness of this arrangement is considerable. A flash of light is able to carry a message, because light that blinks on and off at tremendous speed can represent letters, pictures, and sounds. Signals traveling through glass fibers can convey a vast amount of information while losing very little strength along the way. For this reason, many telephone and internet lines now rely on them.

Certain bundles of fibers carry ordinary light instead, allowing people to direct a beam into narrow places and observe what lies inside. In either job, a strand of glass as thin as a hair guides light wherever it needs to go.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put optical, core, shallow, zigzag and bundle on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 4 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "A Glass Thread That Carries Light Around Corners"?

It was written for 5th grade. It has 213 words and works out to a Flesch-Kincaid grade level of about 5.3. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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