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Natural Science - Year I

Unit 20 Lab: Lens Optics

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Lab: Optics

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Natural Science Unit 20 Laboratory Activity: Optics

Goal: To measure the magnification and focal length of at least two lenses.

Materials and Equipment:


For each lens:

  1. Make a mark 1 unit (inch, centimeter) long on your paper.
  2. Using a light source, (window or ceiling light), focus the image of the light source on your piece of paper.
  3. Measure the distance from the paper to the lens. This is the image distance (focal length).
  4. Measure the distance from the light source to the lens. This is the object distance.
  5. Hold the lens so that you can see the mark on the paper comfortably, and the image is larger than the actual mark on the paper.
  6. Draw the image at the size it appears through the lens next to the mark on paper.
  7. Measure the image length you drew.
  8. Divide the image length by the actual length of the mark. For example, if your mark was 1" and your image drawing was 1.5", you would divide 1.5 by 1 to get a magnification of 1.5 X.
  9. Divide your object distance (from #4) by the focal length (from #3). This is also a measure of magnification.
  10. Are the two magnification measurements the same? Why or why not?
  11. Repeat for at least one more lens.

Data Analysis

  1. Organize your data in a coherent form (organize it into a table, if possible).
  2. Create a graph of important relationships, i.e., size of image relative to distance between the lens and the object.
  3. Explain deviations in your measurements (why do you think any measurements you made are in conflict?)


  1. Describe your equipment and procedure. Note in particular any deviation you had to make from the instructions above to accommodate your equipment.
  2. Describe your lenses; in particular, note if you can whether they are concave or convex, and which is more curved.
  3. Present your data, calculations, and conclusions about this set of observations.
  4. Summarize your findings: how do you think the focal length is related to the lens' curvature?