Eye Models Category: Biology: Human Body, Light & Optics Type: Make & Take Rough Parts List: Box Model: 1 2 1 1 1 1 2 CD case Paint paddles Rubber band Plastic magnifying lens Sheet black paper, 8.5” x 11” Sheet black paper, 11” x 14” Small blocks or corks Colored construction paper Wax paper Pinhole Model: 1 3 Small plastic condiment cup Different sized nails Duct tape Frosted scotch tape -­‐OR-­‐ Clear scotch tape and wax paper Tools List: Electrical tape Masking tape Hot glue gun Scissors Video: https://youtu.be/Iumq0qtYk6c How To: Box Model: © 2015 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. Take apart a CD case. Save all the pieces Use scissors to open the hole where the CD sits. This opening represents the pupil. Cut colored construction paper the same size as the CD. Cut a circle in the center. This colored paper represents the iris. Cut a circle in the center of the paper insert from the back part of the CD case. Place the items in this order: Back part of CD case, then the green circle on top of it, then the paper insert on top of the green circle. In this view, you are looking at the back part of the CD case. Snap the top of the back part of the CD case together, enclosing the papers. © 2015 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. Break the handle off the magnifying glass. This represents the lens of the eye. Glue the magnifying glass onto the CD case. Be careful not to place any glue on the center hole. Snap the connecting tabs off the front piece of the CD case. Tape wax paper across the front piece of the CD case. This represents the retina. Glue a small block or cork onto one end of each paint paddle. Glue the pieces of CD case onto a block. © 2015 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. Use electrical tape to tape the 8.5” x 11” paper to the bottom of the CD case (the piece with the iris and pupil). Fold the 11” x 14” paper in half and center it over the top of the CD case with the iris and pupil. Tape around the top and side edges of the CD case to form a box. Tape along the side edges to seal all the edges and form a big paper box. Slide the second paddle and CD case into the box. Wrap rubber bands around the two paddles to keep them together. Turn down the lights. Aim the eye model at a backlit source like a door or window. The image will project itself upside down and backwards onto the back (wax paper covered) CD case. © 2015 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. Pinhole Eye Model: Wrap the plastic cup in duct tape. Tape frosted tape or wax paper across the open end of the cup. Push the smallest nail through the cup to make a hole. Pull out the nail. © 2015 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. Turn down the lights. Hold the cup in your hand and block as much light as possible. Point the cup at a backlit object. The image will project onto the wax paper or frosted scotch tape. Fine Points: → Use the models in a dark space. → Point the models at a backlit source such as a window to get the best image. It is easiest for kids to see the reversed image when they are looking at something that is moving – such as cars driving by. Concepts Involved: •
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The front surface of the eye is called the cornea. It is hard, and protects the lens. The inside back surface of the eye is called the retina. It is made up of nerves that receive the image made by the lens and send the information on to the brain. The eye changes focus to see things far and near. A real eye does this with muscles that change the shape of the lens. Focus Questions: 1. Draw a diagram of your eye model and label the following parts: the pupil, retina, lens, and cornea. 2. Why do you need the black paper box around the eye? 3. Is the image that is projected onto the retina of the eye model exactly the same as the image that the eye model is pointed at? How is it different? 4. Point the eye models at a window while someone is walking back and forth in front of it. What do you notice about the projected image? 5. What happens to the image on the wax paper if you cover part of the hole letting the light through the lens? 6. Poke a second hole into the pinhole eye model. What do you notice about the projected image? 7. What would happen if you poked 3 or 4 holes into the pinhole model? Elaboration: We gain most information through our eyes. Scientists try hard to understand the eye because sometimes it can trick the brain. This model works well to show the cornea (CD case piece on the front), the iris (back piece of CD case), pupil (hole in the CD case), lens (magnifying glass), and retina (CD case © 2015 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. piece covered by waxed paper). The black paper represents the globe of the eyeball, but has another function as well. It is always useful to consider the limitations of a model. In this model, focusing is achieved by moving the lens with respect to the waxed paper. In your eye, the lens itself can change shape, thus changing its focal length. In your eye, there are two types of transparent fluid: aqueous humor between the cornea and lens, and vitreous humor filling up the majority of the eye globe between the lens and the retina. Finally, there is no one standing behind your eye to report on the image that falls on the retina. The retina is composed of many tiny light-­‐sensitive nerves (the highest concentration of nerves in the body), which are connected to the brain by way of the optic nerve. If you can find a cow or sheep eye you can dissect it to see all these parts. Cut a small hole in the side of the cow eyeball before you start and then shine a light in the pupil. You will be able to see the upside-­‐
down image of that light on the retina. Once you remove the lens from a cow eye, you can use it to project an upside-­‐down image on a piece of paper. The function of the black paper in this model, and the purpose of the large black cloak used 100 years ago by photographers, is to block out other light in order to see the dim image on the screen (retina). Let’s say you are viewing a sun-­‐lit stop sign with your eye model. The image you see is made up of light that came from the sun, bounced off the sign, and then entered the eye model through the aperture (pupil) and lens. If sunlight or other reflected light were also allowed to reach the retina directly, it would overwhelm the dim image of the stop sign. If you cover part of the pupil, less light gets in so the image is not as bright. At the same time, it may be clearer because a smaller part of the imperfect lens was traversed. In the pinhole model, a tiny hole creates a dim image by itself. There is no focusing necessary – the image changes size depending on the distance from the hole to the screen. This is the way pinhole cameras work, and some focus-­‐free binoculars and cameras. Two holes will create two images – try it! The translucent wax paper serves an important purpose: When an image falls on it, one can view it from either side. Old-­‐time photographers used frosted glass for the same purpose. An image would form on any thing placed at the proper distance behind the lens, but most things, such as a normal piece of white paper, would only display the image to viewers on the lens-­‐side of the paper. It is possible to build a model like this large enough to seat several people within. The people then sit with their backs to the lens and view the image on a white screen. This is known as “camera obscura” and we have another project write-­‐up to show you how to make one. You can also make your own camera obscura without a lens. You can make one in your own room if you can get it dark enough, and then leave a tiny hole in one window. You’ll see the scene outside the window, only upside down. Why are all these images upside down and reversed right to left? The answer is simple, but still takes some considering: Light (usually) travels in straight lines. If you are viewing a tree with the eye model, a few rays of reflected light will pass into the model through the lens. Lenses bend light as it passes through them, so the light coming from the top of the tree is bent © 2015 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included. up a bit as it goes through the lens, but still ends up near the bottom of the waxed paper. The light coming from the bottom of the tree is bent down a bit as it goes through the lens, but still ends up near the top of the paper. Meanwhile, the light ray going exactly through the center of the lens does not bend at all and ends up in the center of the paper. The end result is an upside-­‐down image. This happens both on the wax paper of this model and on the retina of your eye. This same process happens with just a pinhole and no lens. If you put a simple convex lens in the system, light does bend going through the lens. It’s called refraction and that’s how lenses focus light. But the rays still end up in the same reversed places. Meanwhile, the light ray going exactly through the center of the lens does not bend at all and ends up in the same place as it would with just a pinhole. Links to k-­‐12 CA Content Standards: Grades k-­‐8 Standard Set Investigation and Experimentation: Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other strands, students should develop their own questions and perform investigations. Grades k-­‐12 Mathematical Reasoning: 1.0 Students make decisions about how to approach problems: 1.1 Analyze problems by identifying relationships, distinguishing relevant from irrelevant information, sequencing and prioritizing information, and observing patterns. 1.2 Determine when and how to break a problem into simpler parts. 2.0 Students use strategies, skills, and concepts in finding solutions: 1.1 Use estimation to verify the reasonableness of calculated results. 1.2 2.2 Apply strategies and results from simpler problems to more complex problems. 1.3 Use a variety of methods, such as words, numbers, symbols, charts, graphs, tables, diagrams, and models, to explain mathematical reasoning. 2.5 Indicate the relative advantages of exact and approximate solutions to problems and give answers to a specified degree of accuracy. 3.0 Students move beyond a particular problem by generalizing to other situations: 3.1 Evaluate the reasonableness of the solution in the context of the original situation. 3.2 Note the method of deriving the solution and demonstrate a conceptual understanding of the derivation by solving similar problems. 3.3 Develop generalizations of the results obtained and apply them in other circumstances. © 2015 Watsonville Environmental Science Workshop. All Rights Reserved worldwide. When linking to or using WESW content, images, or videos, credit MUST be included.