Natural Science Unit 20 Laboratory Activity: Optics
Goal: To measure the magnification and focal length of at least two lenses.
Materials and Equipment:
- Two lenses of different sizes, preferably concave
- Yardstick or meterstick
- Paper and pencil
- Light source
For each lens:
- Make a mark 1 unit (inch, centimeter) long on your paper.
- Using a light source, (window or ceiling light), focus the image of the light source on your piece of paper.
- Measure the distance from the paper to the lens. This is the image distance (focal length).
- Measure the distance from the light source to the lens. This is the object distance.
- 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.
- Draw the image at the size it appears through the lens next to the mark on paper.
- Measure the image length you drew.
- 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.
- Divide your object distance (from #4) by the focal length (from #3). This is also a measure of magnification.
- Are the two magnification measurements the same? Why or why not?
- Repeat for at least one more lens.
- Organize your data in a coherent form (organize it into a table, if possible).
- Create a graph of important relationships, i.e., size of image relative to distance between the lens and the object.
- Explain deviations in your measurements (why do you think any measurements you made are in conflict?)
- Describe your equipment and procedure. Note in particular any deviation you had to make from the instructions above to accommodate your equipment.
- Describe your lenses; in particular, note if you can whether they are concave or convex, and which is more curved.
- Present your data, calculations, and conclusions about this set of observations.
- Summarize your findings: how do you think the focal length is related to the lens' curvature?
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