Topic: Lasers Title: Discount Lenses (Gelatin Wave Guides)
Grade Level/Course: Grades 9-12 Time Frame: One class period
Contributors:
Stan Hutto
Theo. Roosevelt H.S. (NEISD)
slhutto@tenet.edu
 Rachel Lawson
Theo. Roosevelt H.S. (NEISD)

 Jan Mayberry
R.L. Turner H.S. (CFBISD)
mayberry@cfbisd.edu
Overview:
A study of the attributes associated with the concept of fiber optics is done using a labmade fiber optic from clear molded gelatin. A variety of shapes can be cut and pieced together to form a conduit to transmit the laser beam by internal reflection.
TEKS Correlation:
Integrated Physics & Chemistry - Grade 9 or 10
*112.42  The student is expected to:
c1A demonstrate safe practices during field and laboratory investigations.
c2A plan and implement investigative procedures including asking questions, formulating testable hypotheses, and
       selecting equipment and technology.
c2B collect data and make measurements with precision.
c2C organize, analyze, evaluate, make inferences, and predict trends from data.
c2D communicate valid conclusions.
c3A analyze, review, and critique scientific explanations, including hypotheses and theories.
c5B demonstrate wave interactions including reflections within various materials.
c5C identify uses of electromagnetic waves in various technological applications such as fiber optics.

Physics - Grades 10 - 12
*112.47  The student is expected to:
c1A demonstrate safe practices during field and laboratory investigations.
c2A plan and implement experimental procedures including asking questions, formulating testable hypotheses, and
       selecting equipment and technology.
c2B make quantitative observations and measurements with precision.
c2C organize, analyze, evaluate, make inferences, and predict trends from data.
c2D communicate valid conclusions.
c2E graph data to observe and identify relationships between variables.
c2F read the scale on scientific instruments with precision.
c3A analyze, review, and critique scientific explanations.
c3B express laws symbolically and employ mathematical procedures including vector addition and right-triangle
       geometry to solve physical problems.
c8A examine and describe a variety of waves propagated in various types of media.
c8B identify the characteristics and behaviors of electromagnetic waves.
c8C interpret the role of wave characteristics and behaviors found in medicinal and industrial applications.

Technology Applications (Computer Literacy) - Middle School  

*126.12  The student is expected to:
c2A demonstrate proficiency in the use of a variety of input devices.
c4B apply appropriate electronic search strategies in the acquisition of information.
c7B create and edit spreadsheet documents using all data types, formulas and functions, and chart information.
c7G integrate two or more productivity tools into a document including tables, charts and graphs.
Goals and Objectives:
  • Observe refraction and internal reflection and the role they play in wave guides/fiber optics.
  • Collect data and organize it into a useful format.
  • Manipulate variables to determine correlations.
  • Study the uses of fiber optics in industry.

 
Prerequisite Skills/Knowledge:
  • The student should be familiar with spreadsheet and graphing software.
  • The student should be able to use a protractor.
  • The student should be familiar with the terms used in geometric optics.

 
Materials/Equipment Resources:

__Laser
__Knox gelatin
__Flat bottom pan (like a cake pan)
__Bowl, spoon, heat resistant container and hotplate
__Knife for slicing the gelatin
__Light probe and associated software and hardware (MBL/CBL)

 
Instructional Activities/Strategies:

Preparation:

  1. Prepare the gelatin at least one day before the lab. Use 4 packages of the gelatin in one cup cold water to soften.Add 2 to 3 cups of boiling water and stir until dissolved. Put into a flat pan so that the result is about 1 inch thick. Refrigerate until use. Will keep several days.
  2. Assign the students to do Internet research on fiber optics.
  3. Review laser safety with the class.

Classroom management: 
Divide the class into groups so that each group will have a laser, computer light probe with software, and a computer. If only one setup is available, this can be done as a whole class project.

Questions to investigate:

  1. How much light is lost in each centimeter of straight segments?
  2. How much light is lost if the strip is bent 10 degrees? 20 degrees? 30 degrees?
  3. How much can the strip be bent and still transmit light?
  4. Does the width of the strip matter?
  5. What is the index of refraction of the gelatin?
  6. What is the cost per meter of the gelatin fiber optic?

Data Collection:

  1. Slice the stiff gelatin into narrow strips and place on the lab table. Shine the laser through the narrow end of the strip.
  2. Use a light probe to measure the amount of light emitted from the end of the gelatin strip.
  3. Lengthen the gelatin fiber optic by adding another strip. Fit the ends together tightly.
  4. Measure the amount of light emitted by the longer strip.
  5. Keep a chart as as more strips are added.
  6. Bend the strip(s) through various angles and measure the light emitted.
  7. Cut various shapes from the gelatin such as prisms, squares, and lenses to measure other properties such as index of refraction. Do this by placing the shape on paper and outlining the shape with a pencil. Students then direct the laser beam through the shape having the beam strike the incident at an angle. They then determine the point of entry and the point of exit from the form. Marking these points on the paper, the gelatin shape can then be removed. Connect the entry point with the exit point and measure the angle of incidence and the angle of refraction. From this the index of refraction can be calculated.

Calculations:      

  1. Use a spreadsheet for organizing each set of data.
  2. Let students choose an appropriate style of graph for illustrating the data.
  3. Compare the index of refraction of the gelatin with that of other materials.

Communicate results:

Encourage students to compare the results from their gelatin optics with those they discovered from researching actual fiber optics. Students can present their work in written form or as a poster project.

 
Assessment:
  • Evaluate the data table, graphs and charts to indicate the correlation students found between the various variables.
  • Evaluate the quality and the depth of research that was done.

 
Teaching Suggestions/Extensions:

 

 

 

 

 

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