Download Optics Lesson Plan - MRSEC - Utah

Optics for Eyes: Lessons in Light and the
Materials We Use to Correct Vision
Introduction
Many concepts in the “properties of light” component of the 6th grade Utah science
core curriculum can be demonstrated using various lenses and simple laser pointers.
These concepts include: reflection, refraction, transmission, and absorption.
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 using
laser pointers.
Supplies needed:
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1 green and at least 2 red laser pointers
Glass lens and prisms sets (For iDoc activity, 2 biconcave, biconvex lenses will be
used)
Acrylic refraction cell set
Red and green food coloring
Optics for Eyes Demonstration Videos (You Tube Link)
Laminated work mats (iDoc, shape maze)
Optics Lab Book
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
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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)
***This entire kit is available for check out through the College of Engineering. Contact
info located at the end of this lesson plan.***
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 glass, 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.
Lenses:
Bi-convex lens ()–works oppositely to a bi-convex or plano-convex lens in that rays that
exit the lens converge (come together). Students can trace out the path of incident and
transmitted rays and will find that the transmitted rays converge into each other.
However, if you trace the paths of the exit rays backwards, they will all diverge to a
point on the same side of the lens as the laser pointer.
Bi-concave lens )( – A bi-concave 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.
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 basic understanding 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. They will learn about the absorption of colors of light using the red and
green lasers and the refraction cells.
Lesson 1 - The Human Eye and Concave vs. Convex Lenses
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?’ 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. Allow
students to share what happens to light when it strikes various surfaces.
4. Ask students, ‘What do we call it when light bends?’ Review refraction.
Lesson:
5. Ask, ‘What are lenses? Where can we find lenses?’ Teach the two basic shapes to
lenses concave and convex and what they do to light using the glass prism
lenses. 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.
a. Watch Bill Nye: The Eyeball if available.
8. Ask students, ‘What happens when someone can’t see correctly? What do we
use?’
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. An example of this lesson is included on the iDoc video.
Activity and Assessment: Be the ‘i-Doc’
1. 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 i-Doc pages, 2
lasers, and 1 biconcave and 2 biconvex lenses
2. Explain to the students that they are going to be eye doctors today. The lasers
represent the light entering into the eyeball. One of the biconcave lens
represents the lens of the eye. The other biconvex lens and the concave lens will
be used to “correct” vision!
3. 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.
4. 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.
Angle Tangle & Prisms
1. 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
o Red laser
o 2-4 Index cards
o Ruler
o Scissors
o Pencil or pen
o Protractor
o Lab Book or note paper
1. Give each student the triangular prism shapes, 2-4 index cards, laser, ruler,
protractor, 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 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 in their 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, just measure them
with the protractor to verify. Have the students label these angles using the
degree found with the protractorin their Lab Book.
To demonstrate that these angles are always equal:
6. Have the students take an index card and a 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 prism, point of exit from the prism 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. Measure the degree of the angles with the protractor to
verify.
11. Students can repeat this activity several times recording different angles of the
same shape or using different triangular shapes.
See the Angel Tangle video for an example of this activity.
12. Have the students record the results of what they learned in their Lab Book or in
a writing reflection.
Optical Course (Assessment)
Students will be challenged to use the knowledge they have gained to create an
obstacle course using the lenses, 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 Various lenses in differing shapes
Red laser
Paper
Pencil
Optical Course pages
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 Lab Book or notes sheet
Students are divided into groups. Give each group the supplies.
Explain to the students that they are creating a 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 place the lenses, shapes or mirrors, the more
challenging. They cannot move the laser from the ‘Start’ point. They must use
lenses and prisms and or mirrors to reach the end.
At first challenge the students to create the course using only one triangle shape
and have them record their results, then see if they can do it with just a lens.
The next challenge is to create the course using two shapes. Then, challenge
them to create the 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 courses and be prepared to explain how they got the light to move
in the direction they wanted.
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Extensions and Additional Activities
1. Acrylic Refraction Cells (included in kit)
Demonstrate the speed of light, refraction and internal refraction using the
plastic prisms (acrylic refraction cells). Fill them first with clear water and then
with green and the red water. Observe color absorption of the red laser shone
through red liquid. Repeat with the green laser and green liquid. Then try the red
laser in green liquid and green laser through red liquid. Try with other liquids (oil,
corn syrup, rubbing alcohol, vinegar, etc) and observe any affect of changing the
medium through which the laser travels. Record observations. 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.
2. Disappearing Glass
You can further demonstrate refraction this with activity. Find a glass container
and fill it with vegetable oil. (We use a fish bowl) Experiment with different glass
objects (test tubes, small bowl, glass beaker, etc.) Submerge a glass stir stick that
appears to ‘disappear’ when completely submerged in the oil. Some clear straws
work too! This is because the refractive index of the oil is almost exactly the
same as the refractive index of the glass object or straw. They are bending light
in the same way and at the same speed so the glass/straw 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
HAPPY LIGHT BENDING!!!
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
All videos mentioned above can be accessed via the Utah MRSEC You Tube Channel:
https://www.youtube.com/channel/UCIF5Jo03oXIQhDRsyu1hYpQ
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