Communication: Prac (1 Viewer)

[Shire-miss]

hey guys i was wondering if anyone could give me info bout this prac cos we didn't do it!
'bla bla perform a first hand investigation to model the process of accomodation by passing rays of light through convex lenses at different focal lengths'

i know that if i don't do anything it will be in the exam and then.. i'll be kicking myself..thanx heaps

 

[swordfish]

its sort of hard to explain without diagrams...but ill try! what you do is get a light box and use a card with three slits to make three parallel lines of light onto the desk (or whatever you're working on). Then you get a convex lens and place it in the path of the three rays so that they converge on a point beyond the lens. Mark this point in pencil on the desk and measure the distance between the centre of the convex lens and the pencil mark....this is your approximate focal length.
Next take another, fatter convex lens and do the same thing. This distance from the centre of the fatter lens to the point where the light rays converge should be approximately the same distance. It probably wont be exact but, after all, it is only a model.
There are two arguments you can make. You can say that the focal length does change, and measure from the front of the lens to the point of convergence, or you can say that the focal length does not change- and measure from the centre of each lens. (oops, sorry if that confused you).
This experiment models accommodation in the eye....you are able to see how a fatter lens is able to bring the light rays to a point of convergence sooner than a thinner lens does.
I read that back over and it sounded kinda confusing...i hope it was a little bit helpful!

 

[swordfish]

Check and see if this website still exists. if it does, load and watch the animation...it shows clearly the process of accommodation.
http://users.erols.com/renau/eye_applet.html