Third Grade - Science - Lesson 24 - Vision and Optics

Objectives
Experience and describe some optical illusions.
Demonstrate persistence of vision.
Create a moving picture (thaumatrope) based on persistence of vision.

Materials
Optical illusion sheet for each student (attached)
Teacher-made flip book of a jumping man and a thaumatrope (see Teacher's Note)
For each student: blank index card, two rubber bands, scissors, pencil, crayons
Small bathroom paper cups to trace circles on cards and hole punch to share

Suggested Books
Ardley, Neil. The Science Book of the Senses. New York: Harcourt, 1992.
Gregoire, Tanya. Museum of Science Activities for Kids. Holbrook, MA: Adams Media, 1996. Includes many easy-to-do experiments concerning optics, machines, astronomy, human body, plants and animals. Pages 83-84 include directions for making a thaumatrope of a different style.
Sloan, William. The History of Moviemaking. New York: Scholastic, 1994. This spiral-bound book contains many fold outs, overlays, as well as a sample of 35mm movie film. Includes a section on magic lantern presentations as well as illustrations of early motion picture machines such as a phenakisticope, a praxinoscope and thaumatropes like the one students make in this lesson.

Teacher's Note
A flip book can be made from a small scratch or memo pad. Draw a stick figure man standing on the ground and then redraw him the same size on each page, changing his placement so that it appears he is jumping.
To make a thaumatrope, a moving picture toy: Trace around a small paper cup to make a circle on a blank index card. Cut out the circle. Use a hole punch to make a hole on each side of the circle. Try not to punch the holes too close to the edges of the card or the rubber bands may tear through them. Thread rubberbands or string through each hole. Draw a picture on each side of the circle. The classic thaumatrope has a picture of a bird on one side and a cage on the other. Hold the rubberbands and flip the card around several times until the rubberbands are tightly twisted. Release the card. While it is turning, the two pictures seem to blend into one--the bird seems to be inside the cage.

Procedure
Remind the students that in the last lesson they learned about the advantages of binocular vision. Ask: Why are two eyes better than one? (Pictures from two eyes are from slightly different angles. Information from two pictures helps the brain tell how far away something is.) Remind the students about the cardboard-tube-through-the-hand experiment and how the brain blended the images from both eyes and was tricked into seeing something that wasn't there. Ask: What is it called when the eyes trick the brain? (optical illusion) Write this on the board. Tell them that in this lesson they will be exploring some other optical illusions or ways the eyes can trick the brain.

Distribute optical illusion sheets and rulers to students. Tell them that an optical illusion is a trick that happens because our brains make sense out of what our eyes are seeing in two different ways. Discuss each example with the students. Have them use rulers to measure lines and verify what their eyes see.
When the students are finished with the optical illusion sheet, have them look at a bright window or other brightly-lit object in the room for a few seconds and then close their eyes. Ask: What do you see when you close your eyes? (an image of the window or brightly-lit object) Point out that while their eyes are closed, no picture is being focused on their retinas. Ask: Why do you think you still see the window or the object when your eyes are closed? (Accept all answers.) Remind the students that the retina is the eye's movie screen. The picture of the window or object focused on the retina stays there for a short time even when the eyes are closed. Have the students test this by looking at the window again and closing their eyes. Tell them that pictures focused on the retina stay there for a tenth of a second before they start to fade. This is called persistence of vision. The picture persists on the retina. One picture fades while the next is focusing there.
Ask the students if they have ever seen a flip book. Show them the flip book you have made of the jumping man. Point out that each picture in the flip book is a still picture. Ask: When you look at the pictures in the flip book quickly, one after another, why do you think it looks like the man is moving? (One picture persists on the retina and blurs or blends into the next one so it looks like movement.) Ask: Is this an optical illusion? (yes) Have a student come up and show the pictures in the flip book slowly. Ask: Does this optical illusion work when the pictures are shown slowly? (no) Point out that since a picture on the retina begins to fade in a tenth of a second, the pictures must move by quickly, at least ten of them in a second, to show smooth movement.
Ask the students to describe the picture of movie film at the bottom of the optical illusion sheet (pictures connected in a long strip). If available, show the students a sample of movie film or of a film strip. Point out that each frame of the movie film is a still photograph or, in the case of cartoons, a drawing. Point out the holes on the sides of the film. Ask: Why do you think there are holes on the sides of the film? (Accept all answers.) Tell the students that inside a movie projector, wheels with teeth fit into the holes on the sides of the film and pull it past the projection light. The wheels spin so fast that they can pull 24 pictures a second past the light that projects them on the screen. In the movie theater, we see 24 still pictures each second. Ask: If we are watching 24 still pictures a second, why does it look they are moving? (Each picture stays on the retina for part of a second so it blends into the next picture and looks like movement. Our eyes are tricking our brains.) Ask: Do you think movies are an optical illusion? (yes)
Tell the students that more than 100 years ago, before there were movie projectors, children made moving picture toys called thaumatropes (THAW-ma-tropes). Write this word on the board. Tell the students that thauma is the Greek word for wonder. Trope is the Greek word for turning. Thaumatrope means turning wonder. Show the students the thaumatrope you have made. Show them the two pictures and then demonstrate how the turning wonder works. Ask: What do you see when I spin the thaumatrope? (The two pictures blend together into one.) Ask: Is this an optical illusion? Are our eyes fooling our brains? (yes) Tell the students that children used to make collections of thaumatropes with all kinds of pictures. Some had a wild animal on one side and a cage on the other, or a frog on one side and a pond on the other, or the ocean on one side and a sea monster on the other. Distribute materials and have students create their own
thaumatropes.

Possible Field Trip
A behind-the-scenes look at a local movie theater might be arranged by calling the theater manager. Ask if the students might get a peek at the projection booth and see film reels and samples of movie film.

Third Grade - Science - Lesson 25 - Vision and Optics

Objectives
Identify some sources of light.
Observe and record what happens to shadows as light sources are moved.
List objects that are transparent.
Create and perform a shadow play (optional).

Materials
Overhead projector
For each group of five students: an object, a light source (pen flashlight), a large piece of white paper, pencils or crayons.

Suggested Books
Goor, Ron and Nancy. Shadows: Here, There and Everywhere. New York: Harpercrest, 1987. In wonderful photographs and text, this book examines how shadows are formed and how variations in light change shadows.
Lauber, Patricia. What Do You See & How Do You See It? New York: Crown, 1994.
Lynch-Watson, Janet. The Shadow Puppet Book. New York: Sterling, 1980.
Webb, Phila. The Little Book of Hand Shadows. Philadelphia: Running Press, 1990. Contains diagrams of how to create shadow animals as well as verses to accompany them.

Teacher's Note
See Openers and "Speed of Light"- Reading Mastery IV, Lessons 104-105.

Procedure
Tell the students that you are going to read them a poem and you would like them to count how many times they hear this word in the poem. Write the word light on the board. Read the following poem:
You've no need to light a night light
On a light night like tonight,
For a night light's light's a slight light,
And tonight's a night that's light.
When a night's light, like tonight's light,
It is really not quite right
To light night lights with their slight lights
On a light night like tonight.
Anonymous
(light'9; including lights'13)

Remind the students that they have been learning about how eyes and brain work together so that we can see. What is the one thing that eyes must have in order to work? (light) Ask: Where does light come from? (sun) Tell the students that the sun is one source of light. Ask: Can you name some other sources of light besides the sun? List them on the board under light. (lamps, fires, flashlights, stars, nightlights, street lights, neon street signs, matches, candles, lanterns, fireflies, torches, glowsticks) Ask: Is the moon a source of light? (no) Why not? (The moon reflects light from the sun. It doesn't make its own light.)
Tell the students that there is something in the classroom at this very moment that travels faster than anything else in the whole universe. Ask: What do you think that something is? (light) Tell the students that light travels 186,000 miles every second. Write 186,000 miles per second on the board. Tell them 186,000 miles per second is called the speed of light. No one and no thing can travel as fast as the speed of light.
Ask a volunteer to come up and help you with a demonstration. Darken the room, pull down the projection screen and turn on an overhead projector. Have the volunteer stand in its light beam. Remind the volunteer not to look directly into the light. Ask: How fast is the light traveling from the projector to (student's name)? (186,000 miles per second, the speed of light) Ask: What do you think happens to the light after it gets to (student's name)? Does the light go through him/her? Have the volunteer step toward the light a bit and have another volunteer look behind the student and see if light is traveling through him/her. Ask: Do you see any light traveling through (student's name)? (no) What do you see behind him/her? (a shadow) Point out that the light is traveling to the student but not going through or around the student. The student is blocking the light and creating a shadow. Point out that the shadow forms an outline of what is blocking the light. Ask the students to watch (student's name's) shadow as he or she walks toward the projector, or source of light. Ask: What happens to the shadow? (It gets bigger.) Have the volunteer return to his/her seat and show the class how to make an alligator or other hand shadow animal in the beam of light. Point out that we can make shadows because light travels in straight lines, not in curves or zigzags. Have various volunteers come forward and experiment with making other hand shadow animals.
Divide the students into groups of five. Give each group an object, a light source (pen flashlight), and a large piece of white paper and pencils or crayons. Tell the students to place the 3-D object on the paper and shine the light source on it at several different angles. For each angle, trace the shadow of the object on the paper. It is important to hold the light source very still while tracing. Ask: Where is the light source when the shadow is biggest? Where is the light source when the shadow is smallest? What happens to the shadow as the light source is moved away from the object? Tell the students to carefully darken the inside of the shadow tracings with crayons. On the back of the paper, have them draw a picture of the object.
Collect materials and display the shadow pictures on the board. Ask the students to guess from the shapes of the shadows, what objects blocked light to make them.
Tell the students that you have an important question for them that may take a lot of thought. Ask: What can give you the power to see through walls? After a few moments of pondering repeat the question and give the students the answer: windows. Ask: Do windows block the light the way walls do? (no) Why not? (They are made of glass.) Point out that light passes through some things such as glass and clear plastic. When light can pass through things we say they are transparent. Write this word on the board. Tell the students that transparent comes from a Latin word that means appear across. The light hits one side of the transparent glass and then appears across at the other side. If something blocks light we say it is opaque. Write this word on the board. Tell the students that opaque comes from a Latin word that means shady or dark. Objects that are opaque do not let light pass through. They make shadows. Ask: Is (student's name) opaque or transparent? (opaque) Why? (because the light cannot pass through him/her.) Is a light bulb opaque or transparent? (transparent) Why? (because light can pass through it) Ask the students to name some other things that are transparent. (Possible answers might include drinking glasses, windows, windshields, plastic containers, plastic wrap, the cornea of the eye, diamonds, camera lenses, eye glasses, watch crystals, ice and water.) Point out that the students have been examining how light travels from a light source to an object. Tell them that in upcoming lessons they will be looking at how light bounces and how it can be bent.

Additional Activity
The students may enjoy playing with light and shadows and creating a shadow play. Shadow puppet shows have been a popular entertainment in the Far East for centuries. Even today, shadow puppetmaking in Bali is a highly respected craft. In this country, shadow shows without puppets are often performed during the Halloween season. A traditional theme is "The Operation." A sheet is hung and light source and actors placed behind it. The audience, on the other side of the sheet, sees the actors' shadows. A "patient" is seen lying on a table. "Doctors" enter and use props, such as saws, to open the patient. They then begin pulling a variety of improbable objects from the patient ranging from gross to very funny, all easily recognizable by their shadows. Of course, the "doctors" are actually working behind the patient, but the shadow creates the desired illusion. Shadow plays can involve students as actors, stage hands, prop masters, lighting directors, script writers and even sound effects creators. ("The Operation" requires extensive sound effects.) An overhead projector can provide an adequate light source in a darkened room.

Third Grade - Science - Lesson 26 - Vision and Optics
Mirror activities adapted from Showy Science by Hy Kim.

Objectives
Describe how light behaves when it strikes an opaque and a transparent object.
Identify the most and least reflective materials in a group.
Demonstrate the law of reflection.
Use a diagram to create a periscope.

Materials
Piece of aluminum foil, piece of paper, dark-colored sock or cloth
A mirror and a flashlight or other light source
For each group of five students: Two small mirrors, a small object or toy figure, two half-gallon milk cartons (see Teacher's Note), cardboard, tape, glue or rubber cement, ruler, Instruction sheet (attached)

Suggested Books
Aust, Siegfried. Lenses! Take A Closer Look. Minneapolis: Lerner, 1991. Examines human and animal vision and how the telescope and microscope were developed. Includes a periscope-making activity.
Berger, Melvin. All About Light: A Do-It-Yourself Science Book. New York: Scholastic, 1995.
Kim, Hy. Showy Science. Glenview, IL: Scott Foresman, 1994. Includes many simple activities for exploring air, water, light, gravity and motion as well as plants and animals.
Peacock, Graham. Light. New York: Thomson Learning, 1993. Projects include a pin hole camera, periscope and flip book.
Simon, Seymour. Mirror Magic. Honesdale, PA: Boyds Mill, 1991.
Tomacek, Steve. Bouncing and Bending Light. New York: W.H. Freeman, 1994. Written by the star of the PBS show Dr. Dad's Phantastic Physical Phenomena, this book explores reflection and refraction and the history of great discoveries such as Ben Franklin's invention of bifocals and Galileo's use of the telescope.

Teacher's Note
Mirrors used for periscopes should be small enough to fit within the milk carton--about
3 2 x 5 inches. Milk cartons must be prepared ahead of time. Cut off the tops of the milk cartons. Cut a hole 3 2 x 3 2 inches as shown in the instruction sheet (attached). Two cardboard pieces are required for each periscope (the type that comes with shirts is adequate). Cut two strips of cardboard 3 2 inches wide and 12 inches long. Have the students use their rulers to mark and fold the cardboard to form triangles as shown in the directions.
Openers and Reading Mastery IV Lesson 94 deal with reflection and lenses.

Procedure
Remind the students that last lesson they looked at how light travels from a light source to an object. Ask: Can light pass through an object? (yes, if it is transparent) Ask for an example of this. Ask: What if an object is not transparent? What do we call something that is not transparent? (opaque) Ask: What happens when light travels to an opaque object? (The object blocks the light and makes a shadow.)
Tell the students that the reason we can see objects is because light bounces off them and
back to our eyes. Light that bounces off an object is called reflected light. Remind them that the moon has no light of its own, but we can see it because it reflects the light of the sun. We can see objects all around us because they are reflecting light, too. Point out to the students that they can see the board because there is light bouncing off it and back to their eyes. Ask volunteers to come to the front and display the aluminum foil, a dark-colored sock or piece of cloth, and a piece of paper. Ask: If the same amount of light is hitting these three objects, which of them do you think bounces back or reflects the most light? (foil) What makes you think that? (It is smooth and shiny.) Which do you think bounces back the least light? (the sock) What makes you think that? (because it is the least smooth and shiny)
Show the students a mirror. Ask: Do you think a mirror bounces as much light as foil? (yes) Tell the students that mirrors bounce back almost all the light they receive. Show the students the back of the mirror and explain that to make a mirror, a flat piece of glass is coated on the back with a silver paint. Light shines through the transparent glass, hits the silver surface and bounces back. It reflects the light. Demonstrate how a mirror can reflect light from a light source, such as a flashlight, to make a pool of light on the wall or ceiling. Point out that the light hits the mirror at an angle and bounces off it at an angle to make the pool of light. We call this the law of reflection. The law of reflection says that how light hits an object determines the angle it will bounce back.
Show the students a rubber ball. Tell them that light bounces in much the same way that a ball bounces. Ask them to watch the ball carefully as you bounce it a few times on a desk. Point out that when you drop the ball, it travels straight to the ground and bounces back almost in the same straight line. Demonstrate this a few more times. Ask: If I throw the ball so it hits the desk at an angle, what do you think will happen? Try this a few times to show the students that the ball bounces off the desk at the same angle. Draw a horizontal line on the board to represent the surface of the desk and a line to show the path of the ball toward the desk. Ask a student to come up and draw the path of the ball after it hits the desk. Try drawing a different path for the ball approaching the desk and have a student come up and draw that ball's path after it hit the desk. Tell the students that the law of reflection says that light behaves the same way that the ball does. Light bounces off an object at the same angle as it hits it.
Have two student volunteers come up and face each other. Ask the class to imagine that they are watching (student's name) and her reflection in the mirror. Remind the students that the reflection must do everything (student's name) does. Ask the first student to pretend to fix her hair. The reflection will try to imitate every move. (If you think you are more able to play the part of the reflection, take the role.) Ask (student's name) to touch her right ear. Ask: Is the reflection touching her right ear? (No, she is touching her left ear.) Point out that the reflection is reversed. She has to do things backwards. The law of reflection says that light travels from (student's name's) right hand and bounces off the mirror in a straight line. It doesn't cross over. That makes things appear backwards. Have (student's name) hold a book or printed page in front of the real mirror and ask: What do you notice about the reflection of the printed page? (The words and letters are backwards.) Why do you think the letters and words are backwards? (The light from the letters hits the mirror and bounces back in a straight line. It doesn't cross over.) Remind the students that the print is backwards because of the law of reflection. Ask: What do you think happens when two mirrors face each other and light bounces between them? (Accept all answers.)
Divide the students into groups of five and give each group two mirrors and a small object or toy figure. Have them experiment with reflections of the figure. Suggest that they line the mirrors up facing each other with the object in between. Ask: What do you see? How many reflections can you count? What happens when you change the angles of the mirrors? Can you make a reflection of a reflection this way? Tell the students that a special viewing instrument can be built using two mirrors. It is an instrument that sailors in submarines use so they can stay underwater and take a peek above the surface. The instrument is called a periscope. Tell them that periscopes are handy for peeking around corners or over walls because they reflect reflections. Distribute the rest of the materials to each group plus the instructions and diagram of how to build a periscope. When the periscopes are completed, have students try them out by peering over desktops. Point out that the periscope gives a student a view that adds at least two feet to his or her height.

How to Build a Periscope

Materials:
2 milk cartons with the tops cut off and windows cut in the side
2 cardboard strips
2 small mirrors
tape and glue

Instructions:
1. Measure the cardboard strips and draw lines according to the diagram.
2. Fold the cardboard strips along the lines to form triangle wedges and tape ends (see diagram).
3. Glue a mirror on the largest side of each wedge.
4. Glue a cardboard wedge inside each milk carton so the mirror is showing through the window.
5. Put one carton over the other, top-to-top, and tape them together as shown in the diagram. The bottom window should face you and the top window should face away from you.
6. Hide under the desk. Look in the bottom window. Let the top window peek over the top of the desk. What do you see? Is it a reflection of a reflection?
 

Third Grade - Science - Lesson 27 - Optics and Vision

Objectives
Describe the differences in reflections produced by convex and concave mirrors.
Observe how water bends light and works like a magnifier.
Describe the differences between convex lenses and convex mirrors.

Materials
Flashlight
For each group of five students: glass of water, shiny metal spoon, piece of plastic wrap, eye dropper, newspaper, hand lens

Suggested Books
Ardley, Neil. The Science Book of Light. New York: Harcourt, 1991. Includes several activities including building a kaleidoscope and a box camera, as well as an interesting light- bending demonstration.
Darling, David. Making Light Work: The Science of Optics. New York: Dillon, 1991. Although the experiments in this book are for older students, the diagrams and examples are outstanding.
Davies, Kay and Wendy Oldfield. Light. Austin, TX: Steck-Vaughn, 1992.
Gibson, Gary. Light and Color. Brookfield, CT: Copper Beech Books, 1994.
Murata, Michinori. Water and Light. Minneapolis: Lerner, 1984. The explanation of lenses and refraction is very accessible for this age group. Photographs are large and informative. Highly recommended.
Peacock, Graham and Terry Hudson. The Super Science Book of Light. New York: Thomson Learning, 1993. Includes information on starlight, sunlight and lasers as well as lenses and the eye.
Taylor, Barbara. Bouncing and Bending Light. New York: Franklin Watts, 1990. Text is simple and illustrations of reflection and refraction are excellent. A discussion of symmetry includes a page of half objects to reflect in mirrors.
Zubrowski, Bernie. Mirrors: Finding Out About the Properties of Light. New York: Morrow, 1992. This Boston Children's Museum Activity Book is for older children but is chock full of experiments and mirror games.

Teacher's Note
Highly polished stainless steel spoons reflect best.

Procedure
Remind the students that the mirrors they used to bounce light in the last lesson were flat. Ask: What do you think your reflection would look like in a mirror that wasn't flat? (Accept all answers.) Review the law of reflection: the angle at which light strikes an object is the same as the angle at which it bounces away. Ask the students if they have ever looked at their own reflections in a shiny doorknob or a Christmas ball. Point out that these act like mirrors, but instead of being flat, they are curved. A mirror that curves outward like a doorknob is called convex. Draw a convex curve on the board and label it. Tell them that a mirror that curves the other way, in like a bowl, is called concave. Draw a concave curve on the board and label it. Underline the cave part of the word and point out that a good way to remember the difference between convex and concave is to think of a cave going in.
Show the students a spoon. Point to the bowl of the spoon and ask: Is this concave or convex? (concave) Why? (because it curves inward like a cave) Point to the back of the spoon. Ask: Is this concave or convex? (convex because it curves outward) Distribute spoons to be shared and ask students to look at their reflections in the concave and convex sides of a spoon. Are there differences? Have the students write descriptions or draw pictures of how they appear in the concave side and how they appear in the convex side. Have them share their results. Some observations might include: The image is upside down on the concave side except when the spoon is held very close to the eye. Then the reflection of the eye is right-side up. The image also looks a little bigger. On the convex side, faces appear long and skinny or squashed, depending on how the spoon is turned. The reflection changes as the spoon is moved closer or farther away.
Ask the students to think about the law of reflection and how light bounces. Draw a flashlight pointing at the convex curve and draw lines showing the path of the light. Ask a volunteer to come up and draw the path of the light after it hits the convex mirror. How will it bounce? (See the attached diagram. The bounce lines will radiate outward.) Draw a flashlight pointing at the concave curve and lines showing the path of the light. Ask a volunteer to come up and draw lines showing the path of the light after it hits the concave mirror. How will the light bounce now? (The light will bounce back to a point in the inside of the curve.) Point out that both convex and concave mirrors are used on cars. Convex mirrors are used as side mirrors so drivers can get a wide view of what's behind them. Concave mirrors are used inside headlights. Ask: What do you think concave mirrors do inside headlights? (Reflect the light in a straight beam instead of it spreading out.) Unscrew the front of a flashlight and show the students that there is a concave mirror inside behind the light bulb. Ask: What do you think the concave mirror does inside the flashlight? (Reflects the light in a straight beam.)
Point out that mirrors bounce light. Tell the students that light can also bend. Ask: What do you think might make light bend? (Accept all answers.) Divide the class into groups of five students and give each group a glass of water and one of the spoons. Ask: What do we call an object that light can pass through? (transparent) Are you working with anything transparent? (yes, glass, water) How about the spoon. Is it transparent or opaque? (opaque) Ask them to place the spoons in the glasses of water, look carefully at the spoons and describe what they see. Ask: Does it look like the spoon is broken? Is it really broken? Why do you think it looks that way? (Accept all answers.) Point out that light passes through three transparent things before it reaches the spoon--air, glass and water. Remind them that they learned the speed of light is 186,000 miles per second when it is traveling through air. When light travels through water, it travels a little slower. When it travels through glass, it travels even a little bit slower than it does through water. Each time light passes through another transparent substance, it slows down and the light rays bend. Tell the students that the spoon looks as if it is broken because of bending light rays. Ask: Have you ever had trouble reaching into the water and picking something up? When you are looking at it through water, it seems to be in a slightly different place than it really is. By bending light, water can make things look larger.
Have the students flatten a piece of plastic wrap over newspaper. Tell them to use the eyedropper to place a few drops of water on the plastic wrap. Ask: What happens to the letters under the water drops? (They appear larger.) Why do you think they look larger? (Water is bending light and magnifying the letters.) Tell the students that a magnifying glass bends light, too. A magnifying glass is a lens. Have the students hold the hand lenses over the drops of water and look through them at the letters again. Ask: Are they bigger or smaller than with just the water magnifier? (much bigger)
Ask: Is the magnifying lens a convex or a concave lens? (convex) Remind the students that when they studied how the eye works they learned about the lens behind the pupil in the eye that focuses the light on the retina. Draw a convex lens on the board. Draw lines to show the path of light coming into the lens and converging lines on the other side. The convex lens bends light and focuses it in. Ask: How are a convex lens and a convex mirror different? (A lens is transparent and a mirror reflects light. Convex lenses focus light in. Convex mirrors spread out the light that hits them.)
Ask: If I wear eye glasses and use a hand lens to look at the newspaper, how many lenses am I using? (three for each eye, including the lens inside the eye) Ask: Can you name some instruments that have lenses in them? (microscope, telescope, camera, binoculars, projector) Tell the students that these instruments use several lenses stacked up to make things appear larger. Have the students use their convex lenses (hand lenses) to examine the newspaper, their fingertips, drops of water, strands of hair, etc.

Third Grade - Science - Lesson 28 - Optics and Vision
What Color is Black? activity adapted from Seeing in a New Light, a teacher's guide published by the National Aeronautics and Space Administration.

Objectives
Observe how a prism bends light and splits it into a spectrum.
Create a rainbow with colors in spectrum order.
Analyze data from an ascending paper chromotography test of black ink.

Materials
A prism
Bottle of bubbles and some bubble wands
Picture of a rainbow from Suggested Books
Squares or circles of paper (one for each student) in these solid colors: red, orange, yellow, green, blue, indigo (dark blue/navy) and violet (purple)
For each of seven groups of students: a black felt-tip pen, ruler, strip from a coffee filter, glass jar, water, pencil, piece of tape, worksheet (attached)

Suggested Books
Cole, Joanna. The Magic School Bus Makes a Rainbow. New York: Scholastic, 1997.
Darling, David. Making Light Work: The Science of Optics. New York: Dillon, 1991. A good photo of a rainbow can be found on page 45.
Davies, Kay and Wendy Oldfield. Light. Austin, TX: Steck-Vaughn, 1992. Pages 16 and 17 contain photographs of a rainbow and spectrum. The cover of the book pictures a girl painting a rainbow that clearly shows colors in spectrum order.
Lauber, Patricia. What Do You See and How Do You See It? New York: Crown, 1994. Lauber's thorough description of the spectrum and why we see color is fascinating. For those students interested in learning about the wavelengths of light, her book presents the subject without oversimplifying it. Photos of a rainbow and a spectrum are on pages 35 and 36.
Murata, Michinori. Water and Light. Minneapolis: Lerner, 1984. There is a wonderful photo of a rainbow on pages 10 and 11.
Peacock, Graham and Terry Hudson. The Super Science Book of Light. New York: Thomson Learning, 1993. There is a picture of a rainbow on page 20.
Taylor, Barbara. Bouncing and Bending Light. New York: Franklin Watts, 1990. Pages 8 and 9 contain good photos of a rainbow and of a prism throwing a spectrum.

Teacher's Note
The spectrum demonstration can be done with sunlight or projector light. The projector light will produce less green; sunlight will produce a full spectrum. In order to get a clear spectrum of sunlight, you will need a window in which the sun is shining directly.

Teacher Resource
The Seeing in a New Light teacher's guide is available from NASA, Educational Affairs Division, Washington, D.C. 20277-2028. It contains many activities exploring light and color as well as the various wavelengths of invisible light--X-rays, radio waves, microwaves and infrared.

Procedure
Ask: Can you see colors in the dark? (no) Why not? (You need light to see colors.) Tell the students that you are going to ask them a very tricky question. Ask: What color is light? (Accept all answers.) Remind them that last lesson they used water and magnifying lenses to bend light. This time you are going to try to bend light to see what color it is. Show the students a prism. Ask: What shape is a prism? (triangle or pyramid) Point out the three flat faces and the triangle ends. Tell the students that you are going to let a beam of light pass through the prism and see what happens. Orient the prism so a spectrum is projected on the ceiling or wall. Point out that the angles in the prism bend the beam of light and split it into its colors. Ask: What color is light? (all colors) Point out that light looks to be white or colorless but it is really a mixture of all the colors. Tell the students that the bands of color they see on the wall or ceiling are called a spectrum. Write this word on the board. Where have you seen a spectrum before? (rainbows, oil slicks, bubbles) Tell them that the red light on one end of the spectrum is bent the least and the purple or violet light at the other end is bent the most.
Have some students come up and blow soap bubbles. Have them try to "catch" a bubble on a bubble wand to show the colors to the other students. Ask: Why do you think bubbles have rainbows? (Accept all answers.) Tell the students that it may be because light bends as it passes through the edges of the bubble and the light is split into colors. Show the students a picture of a rainbow from Suggested Books. Ask: Does anyone know what makes rainbows in the sky? Tell the students that sunlight shining through raindrops makes rainbows. The raindrops work like prisms to bend the sunlight and split it into its colors. Point out that you can make a little rainbow on a sunshiny day by turning on a hose and spraying water in a mist. When the sun shines through the mist, you can see a rainbow.
Look at the spectrum on the wall or show the students the picture of a rainbow again. Point out that the bands of color are arranged in a certain order. Ask: Can you tell me the colors in rainbow or spectrum order? (red, orange, yellow, green, blue, dark blue (indigo), violet (purple) Write them on the board. Remind the students that white light is all the colors mixed together. Choose a student to be Rainbow Maker. His or her task will be to build a rainbow that circles the room. Distribute a color square or circle to each student. Have Rainbow Maker organize the students into color groups--blues in one corner, reds in another, and so on--and then help the students line up in repeating rainbow order around the room as they display their colors. If available, play a recording of "Somewhere Over the Rainbow" while the Rainbow Maker works. When the rainbow is complete, tell the students that you want each to say his or her color name, starting with the initial red, and see how quickly the soundoff can move along the rainbow.
Have the students return to their color groups. Remind them that we can see what color an object is because light reflects off the object to our eyes. White light, a mixture of all the colors, hits an object. If the object is red, (point to the red group) it absorbs all the other colors of light in the spectrum and reflects red light back to us. If the object is blue, (indicate the blue group) it reflects back blue light. If it is green, (indicate green group) it absorbs all the other colors and reflects back green light so we see it as a green object. Ask: What color light does a black object reflect? Tell the students that a black object does not reflect any color. It absorbs all the colors but does not bounce any back to us. Distribute materials and worksheet to the color groups to try the What Color Is Black? activity.

Possible Homework
Tell the students that people around the world and throughout history have thought of rainbows as magical. They have made up stories about rainbows to explain where they come from and why they disappear so quickly. One idea is that rainbows are bridges from heaven to earth. Another is that there is a pot of gold at the end of a rainbow. Have students write legends of their own explaining rainbows--what are rainbows? Where do they come from? What is their magic?
 

What Color Is Black?

1. Measure 2 centimeters (cm) up from the end of the paper strip and make
a dot of black ink with the felt-tip pen.

2. Tape the other end of the strip to the center of a pencil.

3. What colors do you think will be in the ink? Put a check mark next to these colors on the chart under the "Predicted" column.

4. Rest the pencil on top of the jar so the paper strip hangs inside it. Carefully add water to the jar so that the bottom of the strip is underwater but the black dot is not.

5. Observe for five minutes. Look at the colors on the strip. Make a check mark next to the ones you see under the "Actual" column.

What did you find out about the colors in black ink?

 
 

Color
 

Predicted
 

Actual

Black

Red

Green

Blue

Yellow

Orange

Indigo

Violet


 

 

 

Third Grade - Science - Vision and Optics - January

Bibliography
Read Aloud
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Esbensen, Barbara Juster. Echoes for the Eye: Poems to Celebrate Patterns in Nature. New York: Harpercrest, 1996. (0-060-24399-6)

Reference
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