View source for Physics and Astronomy Labs/Optics: Human eye model (Pasco)


[[File:PASCO Humaneye model1 26355.jpg|Thumb|440px|right]]
==overall impressions==
good lab, with lots of "pluses" and a few "minuses"
====Plusses====
# Students are impressed
# More than two hours of activities are possible
# Most of the images are not clear
====Minuses====
# 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

===Notes===
* 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 {{nowrap|<nowiki><!--this bracket structure--></nowiki>}}

* Three dots (...) are used whenever hidden data is available in edit mode.

page 16

(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 ...<!--p = 320 mm, q=140 mm; therefore f=97mm.  Instructor is dubious about accuracy to more than 10% because we are not sure where to "define" the location of the lens.-->

'''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 ...<!--closer from  32 cm to 19cm.  Very clear.  (Even clearer than before)-->

'''step 9:'''  Replace 62 with 120 mm, as expected ...<!--object distance was moved back.  Less clear, but still good image.-->

'''step 10:'''  Return to only the 62 mm lens in septum slot.  Move object to near point distance.  <s>The pupils reduced intensity with little or no improvement in the already celear image. </s> 

'''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 ...<!-- the +120mm lens, no pupil to "stop" the rays-->

'''step 13:'''  This part worked very well, except for confusion about the meaning of the ''hint''.  Instead, remind the students that the formula,
:<math>\frac 1 p + \frac 1 q = \frac 1 f</math>

has a very simple solution either ''p'' or ''q'' is very large<ref>"very large" and "infinity" are essentially synonyms in this context</ref>.  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 ...<!--success.  The object distance 240 mm from the image to the outer cornea.  The crystalline lens was 62mm.  They removed it and inserted "glasses" in slot 1 (furthest from the retina) with a 400 mm lens, and were unable to focus. They then tried a 120mm lens and it worked.   -->  





Then we started playing astigmatism and blind spot.  Soon we abandoned the pasco equipment and explored the anti-pinhole camera.

==Class edit subpages==
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a;;

[[Category:Physics and Astronomy/Labs]]