Physics and Astronomy Labs/Optics: Human eye model (Pasco)
good lab, with lots of "pluses" and a few "minuses"
- Students are impressed
- More than two hours of activities are possible
- Most of the images are not clear
- Lots of small parts
- One of the devices leaks
- You need a really bright light (not provided) to illuminate the source
- Not all of the images are good: We found that object distances of more than one meter created barely discernible images. Also, the option of an adjustable focal length lens does not seem worth the bother (and it makes a poor image).
Notes on manual
Purpose of these notes
The intent of these notes is to guide the students and instructor through Instruction Manual 012-13032A available at ftp://ftp.pasco.com/support/Documents/English/OS/OS-8503/Human%20Eye%20Model%20Manual%28OS-8503%29.pdf
- The notes were developed to this level after working with 3 students in a science education course on 4/9/2015
- The numerical values obtained are not visible to the reader, but they can be seen by going into Wikiversity's "edit" mode as comments, which are indicated by <!--this bracket structure-->
- Three dots (...) are used whenever hidden data is available in edit mode.
(Should review, thin lens formula, near and far point distances)
Steps 1-3 were skipped because the adjustable lens is a pain. If the eye leaks, place a shallow pan underneath it.
step 4: Filled with water and got image in focus at approx 35 cm. Used +400 mm internal lens. We were unable to get a clear image.
steps 5 and 6: Replaced 400 mm lens with 62mm. Everything went fine. Used a 60 watt frosted bulb. Image was about 10 cm high. We could see great detail. Bulb was held inches away from the picture.
step 7: This where the manual encounters the thin lens formula and far and near point. We only estimated focal point, but it looked like an easy calculation. Class got ...
step 8: Added the 400 mm lens next to the 62 mm (in parallel, next to each other). Simulates adjustment of crystaline lens) Image moved ...
step 9: Replace 62 with 120 mm, as expected ...
step 10: Return to only the 62 mm lens in septum slot. Move object to near point distance.
The pupils reduced intensity with little or no improvement in the already celear image.
step 11: Students asked to draw, but they have already seen and practiced ray diagrams in the past. We are concerned about asking students to make "detailed drawings" with no supervision. For example, do one that is supervised first. Or, it a student invents a sketch, celebrate but check for accuracy.
step 12: The class obtained on by moving object distance to 84cm. They used ...
step 13: This part worked very well, except for confusion about the meaning of the hint. Instead, remind the students that the formula,
has a very simple solution either p or q is very large. That concept can be tested here, although 84cm is hardly "infinity". But you do find that q and f are not too different in magnitude.
step 14: The operation would be considered a success if the glasses worked, and a failure if not. It was a ...
Then we started playing astigmatism and blind spot. Soon we abandoned the pasco equipment and explored the anti-pinhole camera.
Class edit subpages
- "very large" and "infinity" are essentially synonyms in this context