Vision and Optics: Light and Lenses
Using the Learning Cycle
Title:
Vision and Optics: Light Through LensesCourse: Lesson can be utilized in Physics, Biology, or Physical Science
Goal of Lesson: Students will gain a conceptual understanding of the functioning of the Human Eye in relation to optics and optical vision correction. Students will explore optics with light sources and various lenses, relating these to visual acuity, accommodation, near point, blind spots, focal length, object/image distance as well as testing their vision with a Snellan Eye Chart. Relationships between lens type, size, thickness and focus distances will be addressed along with aberrations, astigmatism and far and near sightedness. Students will be able to link optics to related career fields and technological applications. Direct comparison between properties and functions of lenses and the human eye will be made apparent with a model of the human eye.
Possible Student Misconceptions:
# Misunderstanding of how the human eye works
# Lack of knowledge of the necessity and role of light and reflection in vision
# Confusion about the functions and applications of lenses
Prerequisites: Study of refraction (bending of light) and Snell’s Law, and knowledge of how convergent and divergent lenses affect light is necessary in previous learning cycles.
Safety: Students shuld be warned about putting sharp objects near their eye. Viewing unusally bright light sources through lenses should be avoided.
I. EXPLORATION
Student conceptions about vision and the eye will be challenged using discrepant and problem oriented events.
Objectives:
1) Student will check results for their visual acuity using a Snellan Eye Chart.
2) Student will develop questions about vision and visual correction based on experiences.
3) Student will be able to determine their near vision point and develop partial concepts of visual acuity, visual accommodation, astigmatism, and peripheral vision.
Materials: Snellan Eye Chart(s) (1 per group), index cards (2 per group), Question Sheet #1, Worksheet #1 (1 per student), chart with radial lines (to test for astigmatism) (1 per group), Triangle Cylinder Discrepancy with 3 holes punched in one end and one in the other (1 per group), straight pins or toothpicks (1 per group), ruler (1 per group), 5 lenses in a baggie (one or two concave and the rest convex of varying thickness and focal lengths, tape (1 for 2 groups), parallel light source (overhead projector) (1 for each 2 or 3 group3), white index cards (2 per group), black index cards (2 per group), meter stick (1 per group), marker pens (1 per group).
Procedure:
A. Students should work in assigned heterogeneous groups of 4 in which they can assign roles (discussion leader, materials manager, discussion recorder, coordinator- keep on task) and follow directions for responding to the worksheets and testing their vision.
B. Introduce the lesson with a brief comment on the importance of vision to life and the need to understand the functions and health of the eye. Ask the students individually to read, draw, and illustrate Question Sheet #1 before begining lesson activities in groups. Ask the groups to send a person to distribute Question Sheet #1.
1) How does light affect your vision? Draw and illustrate your answer.
2) How do glasses and contacts change your vision? Draw and illustrate your answer.
3) What does the eye chart tell you about how your vision should be corrected?
4) Describe other vision problems people may have? What causes them? Draw and illustrate your answer.
5) How does the human eye work? Draw and illustrate your answer.
Ask the groups to send a person to turn in Question Sheets when complete.
C. Ask the students to work in groups to complete a set of 6 activities. They should discuss all results before writing responses on Worksheet #1 provided. Each student should make sure their results are recorded on their Worksheet #1. They should work as a group helping each other. Tell them they should keep in mind the questions on Question Sheet #1 as they proceed. Ask the groups to send a person to collect and distribute Snellan Eye Chart(s) (1 per group), index cards (2 per group), Worksheet #1 (1 per student), chart with radial lines (to test for astigmatism) (1 per group), Triangle Cylinder Discrepancy with 3 holes punched in one end and one in the other (1 per group), straight pins or toothpicks (1 per group), ruler (1 per group), 5 lenses in a baggie (one or two concave and the rest convex of varying thickness and focal lengths, tape (1 for 2 groups), parallel light source (overhead projector) (1 for each 2 or 3 group3), white index cards (2 per group), black index cards (2 per group), meter stick (1 per group), marker pens (1 per group).
You may wish to provide additional information to the students before they begin.
1) For the first activity (Minimum Distance) ask the groups to work in pairs to test and record the minimum distance at which you can see an object clearly for each person.
2) Next, the students in groups, should take turns testing one another on the (Snellan) eye chart provided. (Stations can be set up around the room for each group-SEE INSTRUCTIONS for setup and testing). Students with glasses should be tested with and without their glasses and students with contacts should make a note of whether or not they are wearing their contacts.
3) Each student in the group should determine the amount of detail the eye can distinguish and record their results on their Worksheet #1 as 20/30, 20/....
4) Students groups should in turn follow directions for testing their automatic adjustment, extent of side vision, possible bluring in their field of vision and the discrepant problem. All results should be recorded by each student on their worksheets.
D. Ask the students groups to compare and discuss their results written on Worksheet #1.
Ask the students to discuss the answers to Quetion Sheet #1 based on their experiences with Worksheet #1.
E. Ask the groups to send a person to collect and turn in all materials.
Evaluation: Collect the students’ question sheets and worksheets from the exploration. Evaluate them considering completeness and specific behaviors drawn or described. Evaluate group skills by assessing whether all participated equally in the activity.
II. INVENTION
Students will be given an introduction to optics and vision using lenses and relationships to the human eye and sight.
Objectives:
1) Student will determine and record the projection orientation, intensity (brightness) and focus (sharpness) of images versus properties of various lenses (type, diameter, thickness and focal length).
2) Student will develop a statement explaining the relationship of the effects lenses have on images.
3) Students will relate terms used to describe vision experiences (and problems) to terms used to describe the functions of lenses.
Materials: Pre-packaged lens sets with concave and convex lenses of various diameters and thicknesses (1 per group), ruler (1 per group), light from outside window (1 per group), worksheet #2 (1 per student), white index cards (2 per group).
Procedure:
A. Group discussion leaders will report the results of their discussion in D. above. The teacher will begin to introduce more appropriate alternative ideas at this time.
B. The teacher will introduce/reintroduce terms and concepts relating to lenses and optics (refraction, reflection, concave/convex lenses, focal point, object/image distance, real/ virtual images, anatomy of the human eye...).
This content can be adjusted to a number of levels of difficulty in various subject areas. More mathematics and quantification may be appropriate in higher level physics classes, whereas more anatomy is appropriate for biology.
C. Student groups will explore the relationships and effects on an image (real/virtual, focus/size...) of various lenses. Use previously assigned roles. See Worksheet #2.
1) The materials manager from each group will obtain pre-packaged lens sets with concave and convex lenses of various diameters and thicknesses (1 per group), ruler (1 per group), light from outside window (1 per group), worksheet #2 (1 per student), white index cards (2 per group).
2) Projection of light from an outside window should be used
3) Students will determine and record the type, focal length, diameter and thickness of each lens and the light intensity (brightness), size, focus (sharpness) and orientation of image for each of the lenses on Worksheet #2.
D. Ask the student groups to discuss in groups the questions "How do lens properties affect light and images?" and "How do these properties relate to how their eyes function?" Selected groups will report their conclusions to the class.
E. The teacher will then explain each of the lens/ image relationships and how they relate to the functions of the human eye. Minimum distance (near point), Snellan eye chart (visual acuity), automatic adjustment, (accomodation), extent of side vision (peripheral vision), and possible bluring in their field of vision (astigmatism).
F. Closure: The teacher should tie in all of the students acquired knowledge from the activities with the actual conceptions and science of optics and vision.
Evaluation: Collect the students’ question sheets and worksheets from the exploration. Evaluate them considering completeness and specific behaviors drawn or described. Evaluate group skills by assessing whether all participated equally in the activity.
III. EXPANSION
Experiences to further transfer properties of lenses and images to the human eye and expand students knowledge of optics in other human experiences.
Objectives:
1) Students will apply properties of lenses to develop a working model of the human eye.
2) Students will explain and apply properties of lenses to vision problems in everyday life.
3) Student will develop a statement explaining the relationship of the effects the eye lens has on problem vision images.
Materials: Pre-packaged lens sets with concave and convex lenses of various diameters and thicknesses (1 per group), clay, ruler (1 per group), parallel light source (1 for 2 groups), worksheet #3 (1 per student), for Model of Human Eye: Florence Flask, slightly milky water (1 per group)
Procedure:
A. Students should work in assigned heterogeneous groups of 4 in which they can assign roles (discussion leader, materials manager, discussion recorder, coordinator- keep on task) and follow directions for responding to the worksheets.
1) Ask student groups to construct a Model of the Human Eye according to instructions on worksheet #3. (If necessary due to time or equipment limitations, the teacher could demonstrate one model.)
2) Students can use the lenses and the model to simulate correction for far and near sightedness, demonstrate inversion on the retina and visual accommodation.
3) Ask the students to answer questions on WORKSHEET #3 in their groups.
B. Ask the students groups to compare and discuss their results on questions on Worksheet #3.
C. The teacher can demonstrate astigmatism with the Eye Model, relating optics to the human eye.
D. The groups should then be asked to discuss and report what the model demonstrates. Each student group will develop a statement explaining the relationship of the effects the eye lens has on problem vision images. The teacher should try to make sure there are few persistent misconceptions.
E. Pass out Question Sheet # 2. Ask the students to discuss, in groups and report, the answers to Quetion Sheet #2 based on their experiences in the lesson.
F. Ask each student group to describe and report how optics applies to other events around them in their daily lives. How are ideas studied in optics useful in possible careers? A guest speaker might be interviewd at this time (e.g. local optomitrist).
G. Summary: The teacher should summarize the sequence of activities and demonstrations conducted.
Evaluation:
The students will be asked to explain the discrepant problem experienced in the EXPLORATION. The students will be given various vision problems (in diagrams or with the Eye Model) and asked to diagnose and provide possible solutions.
Question Sheet #1
Name__________________
Date___________________
Review the following questions, attempt an answer for each one? Keep these questions in mind as you complete the rest of Worksheet #1. Write, draw, and illustrate your answers to these questions.
1) How does light affect your vision? Draw and illustrate your answer.
2) How do glasses and contacts change your vision? Draw and illustrate your answer.
3) What does the eye chart tell you about how your vision should be corrected?
4) Describe other vision problems people may have? What causes them? Draw and illustrate your answer.
5) How does the human eye work? Draw and illustrate your answer.
WORKSHEET #1
Name__________________
Date__________________
1) Determination of the minimum distance at which your eye can focus on an object.
a) Place the beginning of a centimeter scale against your cheek just below your right eye.
b) Have someone cover your left eye with an index card.
c) Hold a pin against the scale and move it along the scale until you find the minimum distance at which you can keep the pin focused.
d) Record this measurement
Without Glasses: With Glasses/contacts:
Right Eye ._______ cm Right Eye N.P._______ cm
Left Eye N.P.________ cm Left Eye N.P.________ cm
2) The amount of detail the eye can distinguish
Snellen Chart- lines of successively smaller letters
1) Subject stands 6.1m (20ft) from Snellen Chart covering one eye with an index card.
2) An observer points out a line to be read by the subject, continuing until a line is reached which the subject cannot read correctly or until all lines are read.
REPEAT FOR THE OTHER EYE
Without Glasses: With Glasses/contacts:
Right Eye _______ Right Eye _______
Left Eye _______ Left Eye _______
3) The automatic adjustment of the eye for viewing at different distances
NOTE: If you normally wear glasses/contacts, leave them on/in.
a) Mark a large capital E on the back of your index finger.
b) Stand 6.1 m (20ft) from the Snellen Chart and hold up you index finger at arm’s length so the "E" on your finger appears beside the large "E" n the top of the chart.
c) With both eyes open, look at the "E" on your finger.
Is the "E" on the chart in focus?
d) Now look at the "E" on the chart.
How many images of the "E" on your finger do you see?
Is the "E" on your finger in focus?
e) Continue to look at the "E" on the chart - close your right eye and open it.
Repeat with Left Eye
What happens to the images of the "E" on your finger?
f) Shift your gaze from the "E" on the chart to the "E" on your finger and back several times. Your eye should automatically adjust and focus for both objects - accommodate. describe results.
4) Extent of vision to the side
1) An observer numbers a paper from 1 to 25. The subject is shown two cards of identical size, one white and the other black. The subject is then seated and stares straight ahead at some distant object.. An assistant sits facing the subject's right ide and somewhat behind the subject. The assistant quickly holds up a card about 30 cm from the subject's head and with the leading edge of the card in line with the posterior edge of the subjec t's eye. The subject, while staring stright ahead, identifies the card as either black or white and the assistant returns the card. The observer records whether the identificaiton is correct or not (use + and -). This is repeated for a total of 25 attempts. Total number wrong _________.
5) Blurring of visual field
1) Stand in front of and about 1.5 to 3 m (4 to 8 ft.) from the chart with radial lines; cover one eye with an index card and look at the center of the chart. All the radial lines appear to have the same darkness to the normal eye: however, the some eyes will see some lines in sharp focus, making them appear darker than the lines that are out of focus. Repeat the test with the other eye. Do you have some blurring in your right eye? _________ in your left eye? ________
If you have some blurring and wear glasses, repeat the test with your glasses on. Do the glasses correct the blurring? __________
6) The TRIANGLE CYLINDER Discrepancy:
1) Hold the 1" cylinder very close to your eye with the three-holed triangle side to your eye, base down as shown.
2) Be sure there is a light behind the hole on the other end of the cylinder (ceiling light).
3) Draw the triangle with the base side down, the way you hold it to your eye.
4) Look through until you see all three corners (vertices) of the triangle in the cylinder.
5) Draw the triangle (holes) as you see them in the cylinder.
Answer these questions as a group task.
1) How do you explain the inversion?
2) Why do you need the hole on the other side of the cylinder?
3) What does this demonstration tell you about the human eye?
WORKSHEET #2
Name__________________
Date___________________
Materials manager should pick up materials on the front table. Discuss your responses to the questions below with your group before writing.
1) Classify (order) the lenses in the baggie according to increasing image intensity (brightness), decreasing focus (clarity), increasing focal length (distance from lens to focused projected object) and decreasing image size. These are predictions. Do not do anything other than look at the lenses.
2) Can you identify possible relationships between lenses and their projected images. List them.
3) Now perform all required measurements and description for each lens in the baggie and record information on Worksheet #2 Continued.
WORKSHEET #2
Continued
Name__________________
Date___________________
Lens #1:
1)Draw the lens and record diameter and thickness.
Diameter___________, Thickness____________ Draw the shape of the lens below
2) Record the following:
Lens type__________________
Focal length________________
Intensity of light (very bright, bright, dim...)
Size of lighted image in best focus_________
Focus of image (very focuses, less focused, blurry...)
Orientation of image (up, down)______
Lens #2:
1)Draw the lens and record diameter and thickness.
Diameter___________, Thickness____________ Draw the shape of the lens below
2) Record the following:
Lens type__________________
Focal length________________
Intensity of light (very bright, bright, dim...)
Size of lighted image in best focus_________
Focus of image (very focuses, less focused, blurry...)
Orientation of image (up, down)______
Lens #3:
1)Draw the lens and record diameter and thickness.
Diameter___________, Thickness____________ Draw the shape of the lens below
2) Record the following:
Lens type__________________
Focal length________________
Intensity of light (very bright, bright, dim...)
Size of lighted image in best focus_________
Focus of image (very focuses, less focused, blurry...)
Orientation of image (up, down)______
Lens #4:
1)Draw the lens and record diameter and thickness.
Diameter___________, Thickness____________ Draw the shape of the lens below
2) Record the following:
Lens type__________________
Focal length________________
Intensity of light (very bright, bright, dim...)
Size of lighted image in best focus_________
Focus of image (very focuses, less focused, blurry...)
Orientation of image (up, down)______
WORKSHEET #2
Questions
Name__________________
Date___________________
Were the relationships that you suspected between lens properties and projected image properties correct ?
Can you use this knowledge to explain events on Worksheet #1? How?
Can you use these lenses to explain or correct far sightedness? Near sightedness? How? Illustrate results.
What do you think would happen if you used combinations of lenses at once?
What is the main function of a lens?
What is the difference between a converging and diverging lens ? (use diagrams)
Why is focal length important, if the object is inside the focal length, what would the projected image look like?
WORKSHEET #3
Questions
Name__________________
Date___________________
Model of the Human Eye
Construct a Model of the Human Eye as instructed below:
Use your lenses to experiment with the "Eye". Can you demonstrate accommodation, inversion, far/near sightedness ?
How would you correct for near-sightedness?
Can you think of other applications for lenses?
Question Sheet #2
Name__________________
Date___________________
Review the following questions, answer for each one? Write, draw, and illustrate your answers to these questions.
1) How does light affect your vision? Draw and illustrate your answer.
2) How do glasses and contacts change your vision? Draw and illustrate your answer.
3) What does the eye chart tell you about how your vision should be corrected?
4) Describe other vision problems people may have? What causes them? Draw and illustrate your answer.
5) How does the human eye work? Draw and illustrate your answer.
DISCREPANT EVENT:
I. Materials manager from each group will then obtain a cylinder and instructions for viewing the triangular image.
J. Each student will view the triangle as directed and draw the triangle on worksheet 1 as they see in both on the copper plate and after looking through the cylinder. (The image of the triangle in the cylinder should be inverted from the triangle image on the copper plate.)
K. Students will discuss the results with their group and attempt to explain the apparent discrepancy.
L. The teacher will ask each group to explain the image seen based on prior knowledge and current exploration, but will not explain the discrepancy until the INVENTION phase of the lesson plan.
4) Detection of blind spot
1) Tape a Visual Map to the wall at eye level. Position yourself in front of the Visual Map with your left eye covered with an index card (if you normally wear glasses for reading, leave them on). Stare at the dot. Have an observed move a pencil, covered with white paper except for its tip, slowly across the map from left to right begining at the dot. When the pencil point seems to disappear, a mark is made on the map. When it reappears, another mark is made. Repeat the procedure going vertically through the blid spot and twice diagonally through the blind spot. Connect the marks with a curved line to complete the map. Measure the approximate map diameter of the blind spot in mm and substitute into the Actual Diameter formula given below. Actual blind spot diameter = ____________ mm.