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The Eyes Have It!

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Author: Muriel Gerhard

Grade Level: 7th - 8th; Type: Human Anatomy

Objective:

Determine which type of lens, convex or concave best resemble the one found in our eyes.

Research Questions:

  • Define light.
  • How does light travel?
  • What is a lens?
  • What is meant by the focal point?  
  • What is the principal axis of lens?
  • What is a real image?
  • What is a virtual image?
  • What is a convex lens? How does it work?
  • What is a double convex lens? How does it work?
  • What is a concave lens? How does it work?
  • What kind of lens do we find in a magnifying hand lens?
  • What kind of lenses do we have in our eyes?
  • Investigate ray diagrams of a convex lens and a concave lens so that you can prepare one for your project. Note how the lines converge or diverge and where you obtain an image.
  • Locate a diagram of the human eye (see provided bibliography) and explain how we actually see an object.

In conducting this project the student is obtaining basic information on what happens to light rays as they pass through convex and concave lenses. Using a hand lens and studying the results, the student deals with the key question of determining whether the image formed with the hand lens and the image formed on the retina of the eye are real images and if indeed they are, why is this case? In the process of conducting the experiment, the student learns and uses the scientific method, constructs a hypothesis, observes and gathers data, analyzes the data, arrives at a conclusion, compiles a bibliography and produces a final report with illustrative diagrams.

Materials:

  • paper
  • hand lens
  • a metric ruler
  • a concave lens
  • a convex lens

These can be purchased from Science Kit of borrowed from the school's science closet or lab.

Experimental Procedure:

  1. Completer all of the arm chair research by answering all of the questions listed under Research Questions.
  2. Gather all the materials you will need for your project. These include paper, a hand lens, a metric ruler, a concave lens, a convex lens.
  3. Prepare a ray diagram using a convex lens. You will use this to record your observations.
  4. Look though a window. Select a shrub or preferably a tree to focus on. Draw a side view of a convex lens in the center of your white piece of paper. Now start at the right side of your lens and draw a horizontal line to the center of the lens. Select a point along the horizontal line that will be the focal point and label it with a capital F.
  5. Now, start at the left of the diagram, at a greater distance from the lens than the focal point is on the right, sketch in the object that you have chosen to focus on.
  6. Now get ready to “take a picture”. On a nice bright sunny day, darken the room, stand at the window, and hold the hand lens 1.5 m from the window at the same level as the object outside. Hold the piece of paper on the opposite side of the lens from the window. Line the paper up with the object.
  7. Formulate a hypothesis. Where do you think the focused object will show up on the paper? What will the object look like? Straight up? Upside down? Smaller? Larger? Record your hypothesis.
  8. Now move the paper back and forth. Get the image onto the paper. Measure the distance between the lens and the paper. Use this measurement to draw the image in its right place.
  9. Review your data. How valid was your hypothesis? How far from the lens did the image appear?
  10. What kind of an image appeared? Was it what you expected? Why?  Why not? Was it smaller or larger than the object? Was it real or virtual?
  11. Now relate this to your research on the human eye. Was the image you formed with the convex lens like the image formed on the retina of the eye? Did you make a match?
  12. Write up your report. Include your diagrams of convex and concave lenses as well as your ray diagram. Be certain to include your bibliography.

Terms/Concepts: light rays; lenses; transparent; reflection; refraction; plane surface; convergent light; divergent light; convex lens; concave lens; focal point; focal length; real image; virtual image

References:

 

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