Jell-O Optics
Introduction
Many concepts in the “properties of light” component of the 6th grade Utah science
core curriculum can be demonstrated using different shapes cut from Jell-O and simple
laser pointers. These concepts include: reflection, refraction, transmission, and
absorption. Additional activities can demonstrate the speed of light, ?
6th grade Utah Science Core
Standard 6: Objective 2
Describe how light can be produced, reflected, refracted, and separated into visible light
of various colors.
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Compare light from various sources (e.g., intensity, direction, color).
Compare the reflection of light from various surfaces (e.g., loss of light, angle of
reflection, reflected color).
Investigate and describe the refraction of light passing through various materials
(e.g., prisms, water).
Predict and test the behavior of light interacting with various fluids (e.g., light
transmission through fluids, refraction of light).
Predict and test the appearance of various materials when light of different
colors is shone on the material.
Objectives
Students will model the path of refracted light through concave and convex lenses, and
yellow, red, and green Jell-O.
They will learn about the absorption of colors of light using the red and green Jell-O.
Timing
2-3 lessons of 30-60 minutes each
Kit Contents
• 5 - 9x9x3.5 Cake pans with lids (lids allow you to stack the container)
(You can also use large flat cookie sheets with a high edge as an alternative)
• 4-8oz. “lemon” flavored Jell-O per pan (follow the Jiggler recipe on the box)
• 4- 8 oz. “lime” flavored Jell-O per pan (follow the Jiggler recipe on the box)
 4- 8 oz. “strawberry” flavored Jell-O per pan (follow the Jiggler recipe on the box)
• Cooking Spray
• shape templates
• 5 - sharp, non - serrated paring knives
• 1 green and 6 red laser pointers
• Glass lens and prism set
• Acrylic refraction cell set
• CD with Jell-O Optics gift kit agreement and Jell-O Optics PowerPoint Lesson,
Demonstration Videos
 Laminated work mats
 Jell-O Optics Lab Book
Additional supplies needed:
• small tip markers
• large sheets of tracing (or butcher) paper
• replacement batteries as needed for laser pointers
• protractors to measure angles
• play dough or clay to hold the lasers in place so they don’t roll during the I-Doc
activities
• paper
• pencils
• rulers
• scissors
• index cards
• Mirrors that can stand up (two mirrors taped together work well or use play
dough or clay to create a stand for the mirrors)
Additional Resources Recommended (More resources listed at the end of lessonplan)
DVD Bill Nye: The Eyeball
DVD Bill Nye: Light and Color
Background For Teachers:
Light rays slow down and may bend when they pass from one material to another. This
bending is called refraction. Refraction happens because light travels at different speeds
in different materials. Light changes its speed when it passes from one material into
another. It travels at lower speeds through dense materials such as water and at higher
speeds through materials that are less dense such as air. A beam of light will travel at a
slower speed in a denser material. It will maintain that same, slower speed until it exits
that material where upon it will resumes it original speed. (speed of light: in a vacuum:
186,000 miles/sec, air: slightly less than 186,000 miles/sec, water: 140,000 miles/sec,
glass: 124,000 miles/sec, diamond 77,500 miles/sec)
Light refracts only when it hits another substance at an angle. When light impacts the
boundary of another substance head-on (perpendicular or 90-degrees) it will slow down
but will not refract. When light hits the substance at any other angle, it will refract. The
angle of refracted light will increase in proportion to the angle of the entry. The angle at
which the light crosses the media boundary and the angle produced after refraction is a
very precise characteristic of the material producing the refraction.
Lenses are used to bend light. They are made of curved glass or other transparent
material. Light always bends towards the thickest part of the lens. There are two types
of lenses. A concave lens is thick on the outside ends and thin in the middle (think of a
cave). A convex lens is thin on the outside edge and thick in the middle.
Teacher’s Glossary
Language science students should use: angle of incidence, angle of reflection,
absorption, medium, prism, reflection, refraction, spectrum
These definitions are for teacher’s use. Teacher will want to develop a student definition
with the students as they discuss these concepts.
Refractive index – the refractive index determines the speed at which light passes
through a medium. A medium denser than air (such as Jell-O, water, oil, etc.) generally
has a higher refractive index and a slower light speed.
Reflection – when light strikes a smooth surface, such glass or a mirror, it is reflected.
The angle of reflection is equal to the angle of incidence, but the reflected ray changes
direction. This is known as specular reflection. Reflection from a rough surface does not
follow this behavior and can be strongly scattered in many directions. This is known as
diffuse reflection.
Refraction – when light enters a medium of a different refractive index (like air - water)
the angle of light changes. This is described by Snell’s Law. When light enters a medium
of higher refractive index, the angle becomes smaller. When light enters a medium of
lower refractive index, the angle becomes larger. In the latter case, if the external angle
reaches 90 degrees, then the beam will completely reflect back into the first medium.
This is known as total internal reflection.
Absorption – materials and objects have different colors largely due to the absorption
of light. Absorption is the process by which light is “lost” in a material, but absorption
depends upon the color of light. For example, a material or object that appears “red”
does so because it predominantly absorbs “blue” and “green” light.
Background for Students
Prior to this lesson students should already have learned about the basic
properties of light: reflection, refraction, transmission, absorption, spectrums, and the
primary colors of light (red, green. blue). They should know that light moves in waves
and in a straight line from its source unless it is reflected or refracted. Light can be bent
or refracted by the medium it travels through.
The refraction of light can be modeled in several ways. One way is to use a prism
and shine a light through it. The colors are separated as each color bends at a different
angle. Another way refraction can be observed is to look at a pencil that is placed in a
cup of water. The pencil appears bent as the light waves slowdown in the water.
Students should have experimented with and have a yellow understand of refraction in
prisms, water, and other liquid mediums. They should be familiar with tracing and
measuring the angles at which light enter and exit a medium. For additional ideas on
how to help students reach this understanding, see "Bending Beams of Light" lesson
plan listed under resources at the end of this lesson plan.
In this activity students will model the path of refracted light through concave and
convex lenses, and yellow, red, and green Jell-O. They will learn about the absorption of
colors of light using the red and green Jell-O.
Lesson 1 - The Human Eye and Concave vs. Convex Lenses
Preparing: Open PowerPoint: Jell-O-Optics Eyes
Prior to this lesson, students have learned about the basic properties of light including
how light travels, when it hits a surface it can be reflected, refracted, transmitted, or
absorbed.
Building Background:
1. Ask students to name their five senses. Then ask them to brainstorm responses
to the question ‘Which of your senses is the most important?’
Introduction:
2. Tell students today we will be learning about the sense of sight and how it work.
Ask students, ‘How do your eyes work?’ (PowerPoint Jell-O Optics Part 1?: slide
2). Allow them to brainstorm with a partner, then share with the class.
3. Review the how light travels and what happens when it strikes a surface. (slide
3). Allow students to share what happens to light when it strikes various surfaces
(slide 4).
4. Ask students, ‘What do we call it when light bends?’ Review refraction (slide 56).
Lesson:
5. Ask, ‘What are lenses? Where can we find lenses?’ (Slide 7). Teach the two basic
shapes to lenses concave and convex and what they do to light using the glass
prism lenses and slides 8-11. One side of the glass prisms is frosted to aid in
revealing the path of light.
6. Demonstrate how each lens will change the direction of a beam of light from two
lasers. (You might be able to do this against a white board if you have kids hold
each part.) An example of this activity is included on the concave-convex lenses
video.
a. Place two lasers parallel to each other and about an inch apart on a flat
surface.
b. Place a small white box about two feet away. Mark the point where the
lasers hit the box.
c. Place the glass biconvex () lens in front of the lasers and show how the
light has changed directions or refracted. Convex lenses cause the light to
come closer together or converge.
d. Place the glass biconcave )( lens in front of the lasers and show how the
light has changed directions or refracted. Concave lenses cause the light
to spread apart or diverge.
7. Explain to students how the eyes work using a convex lens to focus light on the
retina. The image is flipped inside the eye, but the brain interprets the message
and tells what is being seen (slides 12-13).
a. Watch DVD Bill Nye: The Eyeball if available.
8. Ask students, ‘What happens when someone can’t see correctly? What do we
use?’ (slide 14).
9. Explain the two basic problems in sight: near-sightedness and far-sightedness
and how optometrists or eye doctors fix these problems using glasses or
contacts (slides 15-19). An example of this lesson is included on the iDoc video.
Activity and Assessment: Be the ‘i-Doc’
*You may want to wait and have students do this activity at the same time they
do the other activities with Jell-O.
o Divide the students into small groups (The size of the group will depend
on how many lasers you have available). Give each group a copy of the 3
laminated work mats I-Doc, the I-Doc page from Jell-O Optics Lab Book, 2
lasers, and 1 biconcave and 2 biconvex lenses cut out of Jell-O
1. Explain to the students that they are going to be eye doctors today. Walk the
students through how to complete the I-Doc activity. They place the lasers on
the lines so the lit up end is just at the edge of the paper. You may want to give
each group play dough or clay to put a small piece under the lasers to hold them
in place from moving. They place the biconvex () lens inside the ‘eyeball’ on the
spot that says ‘lens’. They will then turn the lasers on. The laser light should
focus on the retina at the back of the eyeball. Have the students experiment with
placing the biconvex () and the biconcave )( in front of the eyeball to see how
that changes the spot where the light focuses.
2. Allow the students to go through the same process to work through the other IDoc work mats. Remind the students that if the light focuses in front of the
retina, the person is nearsighted. If the light focuses beyond the retina, the
person is nearsighted. They will need to figure out which type of lens to make
the ‘glasses’ out of so their patient can see clearly.
Lesson 2
Preparing for Lesson 2
1. The Jell-O trays should be prepared the day before use to allow for proper set up.
The Jell-O needs to be firm enough so that the shapes can be handled without falling
apart, but it must retain sufficient water content to remain transparent enough to
light. You’ll want a final thickness of ½”. Prepare 3 trays of lemon (“yellow”), 1 “red”
and 1 “green” Jell-O.
2. Jell-O Recipe
 Yellow Jell-O – For each pan, follow the Jigglers recipe on the box. Let sit in the
refrigerator until firm, preferably overnight. The pans with lids that have been
provided allow for stacking in the refrigerator and easy transport.
 Red and Green Jell-O – For the flavored Jell-O, follow the recipe for Jigglers on
the package for both the lime Jell-O and strawberry Jell-O.
3. Cutting the Jell-O shapes
Since there is only one set of templates, you will need to cut the shapes out before
the lesson begins. Trustworthy students can cut the shapes out on their own, but they
will have to share the templates.
 Yellow Jell-O
Each pan of yellow Jell-O may need to serve 2 groups so closely space the
shapes. Lay the each of the templates on the yellow Jell–O surface and carefully
trace out each shape with the sharp paring knives. Enough pressure should be
applied to the knives to cut all the way to the bottom of the pan to allow clean
release of the shapes. Make cuts with very smooth edges; rough edges will
strongly scatter light. To release the shapes, it is easier to remove some of the
Jell–O around the shape first, and then the shape can be peeled from the pan.
 Red and Green Jell-O
Each shape can also be cut from the colored Jell-O, but the most important
shape used with green and red Jell-O is the long rod.
Building Background:
Introduction: Review with students the material from the previous lesson: properties of
light, refraction, lenses, and eyesight. Explain to students that light travels differently
through different mediums. Have them predict what will happen to light as it travels
through the Jell-O.
Lesson Procedures
Students can be placed in 5 groups. Cover their work area with butcher paper. These
experiments don’t need to be performed in any specific order, and if supplies are
limited, each group can work on a different experiment, but it would be better if all
students are doing the same experiment at the same time, following-along with the
instructor.
Experiments
A. I-Doc (if not done previously)
B. Angle Tangle & Prisms
2. The purpose of a prism is to bend light and to separate light. The prism can also
be used to demonstrate reflection, refraction, and total-internal reflection.
Supplies for each student or group
o 1-2 different triangular prisms from the yellow Jell-O (use the plastic
template and the glass triangle for both shapes)
o Red laser
o 2-4 Index cards
o Ruler
o Scissors
o Pencil or pen
o Jell-O Optics Lab Book
1. Give each student the one or two triangular prism shapes cut from the yellow
Jell-O, 2-4 index cards, laser, ruler, scissors, and a pencil or pen.
2. Have the students shine the light from the laser pointer through one flat edge of
the triangle and observe what happens to the beam as it passes through the
prism.
3. Have the students change the angle of the beam to make it more acute or
obtuse. By making small adjustments to the angle, students can see the
transition where both a transmitted and reflected beam are produced and
where just a reflected beam is produced. Have them find the point where the
beam is both transmitted and reflected and record their observation in their JellO Optics Lab Book.
4. Next have them find the point where the beam is reflected completely from
another edge of the prism and record their observation on their Jell-O Optics Lab
Book. This is known as total internal reflection.
5. Remind them that the angle at which light strikes a reflection point is called the
angle of incidence. The angle at which a beam of light is reflected off is called
the angle of reflection. These two angles are always equal. Have the students
label these angles on their Jell-O Optics Lab Book.
To demonstrate that these angles are always equal:
6. Have the students take an index card and a Jell-O prism and trace the prism on
the index card.
7. Next, have the students shine the laser into the prism at the angle that shows
reflection.
8. Holding the laser on and steady, students will mark the laser’s point of entry into
the Jell-O, point of exit from the Jell-O and the spot at which it is reflected.
9. Students remove the prism and trace draw the path of the laser using a ruler to
connect the points.
10. Have them cut out the angle of incidence from the index card and flip it over on
top of the angle of reflection. These two angles fit perfectly on top of each other
because they are equal.
11. Students can repeat this activity several times recording different angles of the
same shape or using different shapes.
See Angel Tangle video for an example of this activity.
12. Have the students record the results of what they learned on the Jell-O Optics
Lab Book or in a writing reflection.
C. Long Rod
Long rod – The rod can be used to demonstrate the concepts of reflection, refraction,
absorption (for colored Jell-O), and total-internal reflection.
Supplies for each student or group
o Long rod cut from the yellow Jell-O, red Jell-O, and green Jell-O
o Red laser
o Green laser
o Jell-O Optics Lab Book
1. Students are divided into groups.
2. Have the students observe how the laser passes through the yellow rod.
Challenge them to see how many times they can get the laser to reflect or
bounce within the Jell-O. Have them observe what happens when the light
shines directly into the Jell-O at a 90 degree angle. (The light should be reflected
back.)
3. Have the students shine the red laser through the red Jell-O rod and observe
what happens. Most of the light beam is transmitted.
4. Have the students perform the same experiment except with the green laser and
observe what happens. As they shine the green laser through the red Jell-O rod
most of the light is absorbed rather than transmitted. Students can observe the
rapid drop in light intensity directly within the Jell-O. The reverse happens when
shining light through the green Jell-O rod.
5. Have students perform the same experiment with red and green lasers with the
yellow and then the green rod.
6. Invite students to record their observations and reflect on what they observed.
Ask them to predict why the red light was mostly absorbed by the green Jell-O
and why the green light was mostly absorbed by the red Jell-O. This is a great
opportunity to review and talk about the colors of light and why we see colors.
D. Plano-convex
lens
Plano-convex lens – The plano-convex lens can be used to demonstrate the concepts of
refraction and focusing.
Supplies for each student or group
o Plano-convex lens cut from the yellow Jell-O (use the glass lens as a
template)
o Red laser
o Paper
o Pencil
o Ruler
o Jell-O Optics Lab Book
1. Students are divided into groups.
2. Have the students place the lens flat onto the paper.
3. Shine the red laser pointer on the middle of the flat side of the lens straight on at a
90 degree angle and observe and record what happens (i.e. the beam should reflect
back).
4. Keeping the laser straight on perpendicular to the flat side of the lens and to the
paper students will example the path of the light as it enters and exits the lens.
Starting close to the edge of the lens, students mark and trace the path of the light
from before it enters the lens to the point of entry to the point of exit for the laser
beam to where it goes as it exits the lens. They should repeat this marking and
tracing of the path of light several times, gradually working their way across the flat
side of the lens.
5. Students should notice that the angle of the light beam exiting the curved surface of
the lens is different from the incident beam. This is due to refraction from the
curved face (there should be no change in angle through the straight interface).
6. After performing this tracing for a few different positions, the students should notice
that on the curved side of the lens, the rays intersect (or nearly intersect). This
intersection point is called the focal point of the lens. Parallel rays entering from one
side a lens intersect at the focal point on the other side of the lens. This is a general
property of lenses.
E. Bi-concave lens
Bi-concave lens – A biconcave lens works oppositely to a bi-convex
or plano-convex lens in
that rays that exit the lens diverge (spread
apart) rather than converge (come together). Again, students can trace out the path of
incident and transmitted rays and will find that the transmitted rays diverge from each
other. However, if you trace the paths of the exit rays backwards, they will all converge
(or nearly converge) to a point on the same side of the lens as the laser pointer.
Supplies for each student or group
o Bi-concave lens cut from the yellow Jell-O (use the glass lens as a
template)
o Red laser
o Paper
o Pencil
o Ruler
o Jell-O Optics Lab Book
o
1. Students are divided into groups.
2. Have the students place the lens flat onto the paper.
3. Shine the red laser pointer on the middle of the lens straight on at a 90 degree
angle and observe and record what happens.
4. Keeping the laser straight on parallel to the flat top and bottom of the lens
students will example the path of the light as it enters and exits the lens. Starting
close to the edge of the lens, students mark and trace the path of the light from
before it enters the lens to the point of entry to the point of exit for the laser
beam to where it goes as it exits the lens. They should repeat this marking and
tracing of the path of light several times, gradually working their way across the
lens.
5. Students should notice that the angle of the light beam exiting the curved
surface of the lens is different from the incident beam. This is due to refraction
from the curved face.
6. After performing this tracing for a few different positions, the students should
notice that on the curved side of the lens, the rays diverge (spread apart) rather
than converge. However, if you trace the paths of the exit rays backwards, they
will all converge (or nearly converge) to a point on the same side of the lens as
the laser pointer.
F. Optical Course (Assessment)
Students will be challenged to use the knowledge they have gained to create an
obstacle course using the Jell-O shapes and mirrors. They will have to shine the laser
from the starting point and get the light to reach the target at the finish using and
increasing number of shapes.
Supplies for each student or group
o All the shapes cut from the yellow Jell-O
o Red laser
o Paper
o Pencil
o Laminated Optical Course work mat
o Mirrors that can stand up (two mirrors taped together work well or use
play dough or clay to create a stand for the mirrors)
o Jell-O Optics Lab Book
1. Students are divided into groups. Give each group the supplies.
2. Explain to the students that they are creating an obstacle course. They must get
the light beam of the laser to shine from the starting point to the ending point
target. The closer to the center they get, they more points they earn. They
cannot move the laser. They must use Jell-O shapes and or mirrors to reach the
end.
3. At first challenge the students to create the obstacle course using only one
triangle shape and have them record their results. Then, challenge them to
create the obstacle course using only one rod shape and have them record their
results, then see if they can do it with just a lens.
4. The next challenge is to create the obstacle course using two shapes. Then,
challenge them to create the obstacle course using three shapes, then four, then
five, then add mirrors until they are using all the shapes and several mirrors.
Have them record their favorite mazes and be prepared to explain how they got
the light to move in the direction they wanted.
Extensions and Additional Activities
1. Fiber Optic Cables
Obtain some Fiber Optic Cables. Allow the students to experiment with how the
light travels through the cables. The long rod of yellow Jell-O most closely
resembles the movement of the light inside fiber optic cable. Have them try the
obstacle course using the fiber optic cable instead of Jell-O. Use the videos below
for more information and ideas.
 Fiber optic cables: How they work
http://www.youtube.com/watch?v=0MwMkBET_5I
 Head Rush- Gelatin Fiber Optics
http://www.youtube.com/watch?v=I4pgO3U5luY
2. Acrylic Refraction Cells (included in kit)
Demonstrate the speed of light, refraction and internal refraction using the
yellow plastic prisms (acrylic refraction cells). Fill them with water and other
liquids (oil, corn syrup, rubbing alcohol, vinegar, etc) and demonstrate what
happens when shining the laser through the different liquids. Try shining the
light straight on or at different angles. The cells are excellent for showing
refraction and internal reflection in water and other liquids and to observe the
refractive index.
3. Disappearing Glass
You can further demonstrate refraction this with activity. Find a yellow glass
container and filling it with vegetable oil. (I used a fish bowl) Experiment with
different yellow glass objects (test tubes, small bowl, glass beaker, etc.) You
should be able to find a glass object that appears to ‘disappear’ when completely
submerged in the oil. This is because the refractive index of the oil is almost
exactly the same as the refractive index of the glass object. The oil and the glass
object are bending light in the same way and at the same speed so the glass
blends into the oil and ‘disappears’. See the video below for more information
and ideas:
 Head Rush- Disappearing Glass
http://www.youtube.com/watch?v=gGJb9QX_4K8
This lesson was adapted by Steve Blair, Ph.D, Professor in the Department of Electrical &
Computer Engineering and University of Utah MRSEC Plasmonics Researcher.
This lesson was revised by Anne Bailey, a 6th grade teacher in the Salt Lake School
District.
This Jell-O Optics kit has been provided to select Utah 6th Grade teachers by Utah
MRSEC, supported by the National Science Foundation under grant no. DMR-1121252
CFDA NO. 47.049
Please email the exact number of impacted students, annually, by the end of April, to:
Chelsey Short
University of Utah MRSEC
Education and Outreach Coordinator
[email protected]
801-585-9173
Additional Resources
Fiber optic cables: How they work http://www.youtube.com/watch?v=0MwMkBET_5I
Head Rush- Disappearing Glass
http://www.youtube.com/watch?v=gGJb9QX_4K8
Head Rush- Gelatin Fiber Optics
http://www.youtube.com/watch?v=I4pgO3U5luY
Bill Nye: The Eyeball
clip http://www.youtube.com/watch?v=cFVbLnXWn6A
full http://www.youtube.com/watch?v=UsTHHXh8uL8
Bill Nye: Light and Color
http://www.youtube.com/watch?v=CuQMRNg7Zkk
Resources
Bending Beams of Light
http://www.uen.org/Lessonplan/preview.cgi?LPid=16202