HSC Biology -- Communication Option Questions

[ateenytinybear]

Hey all!
Hoping I can gain a little wisdom before my prac.assessment on communication... The aim is to "model accommodation in the eye by passing rays of light through convex lenses of different thicknesses."

Can anyone can explain to me why accomodation works? Especially in relation to the practical? Because if there is a changing focal length, doesn't that mean its not hitting the retina, and therefore not creating a clear image??? For example, if the lens is thin, the focal length increases, and then... what does it all meeeaaannnn i dont even know what i dont knowwww

lost af~~~

[jasn9776]

OK  i haven't even done this topic but pretty sure i am a science nerd that looks at scientific journals and wears glasses and does physics so i should be qualified.

The convex lenses provide refractive power. This means it makes the light rays converge more. 

The thicker the convex lenses are, the more power it gives and therefore the closer it makes the light rays converge.
More Thick= shorter focal length
Less Thick = longer focal length

Light needs to hit the retina directly in order for it to be a clear image.

The focal length is the length from the middle of the lens to the point where they converge.

Hopefully that helps, just see the link below for a picture of focal length,
http://topdifferences.com/wp-content/uploads/2017/02/converging-lens-300x209.gif

The closer the object the more divergent the light rays are and therefore the more power is required to make them converge on the retina.

In distance vision, the ciliary muscles are relaxed and the lens is pulled flat=less convex=less power
In close up vision,the ciliary muscles contract, suspensory ligaments loosen and the lens is allowed to slacken=more convex=more power The greater power counteracts the more divergent image.

In older people, where the lens is becomes too inflexible to be pulled(presbyopia), convex lenses can be worn over the eye to allow close objects to be seen.

That is why they need reading glasses.  :

Helpful youtube video:
https://www.youtube.com/watch?v=YtpRpttPnHw

Ha ha, communication will be easy for me when I do it in term 3!

Mindless gibberish for my own notes:
Homeostasis controls the length of the eye in baby animals. Animals are often born with eyes too short or too long. The eye homeostatically adjusts its length in order to ensure that the light rays converge on the retina. (Longer eyes provide grater focusing power while shorter eyes provide less)
https://www.sciencedirect.com/science/article/pii/S0896627304004933

[vox nihili]

Hey all!
Hoping I can gain a little wisdom before my prac.assessment on communication... The aim is to "model accommodation in the eye by passing rays of light through convex lenses of different thicknesses."

Can anyone can explain to me why accomodation works? Especially in relation to the practical? Because if there is a changing focal length, doesn't that mean its not hitting the retina, and therefore not creating a clear image??? For example, if the lens is thin, the focal length increases, and then... what does it all meeeaaannnn i dont even know what i dont knowwww

lost af~~~

I think you'd probably gain a lot by looking at some diagrams on Google or having a bit of a squiz at a video on YouTube or something about how lenses work. It's confusing af but when you actually see it explained it's really easy to understand. Basically the idea of a lens though is to focus all of the light onto one point in the retina (the fovea)....if you have a look at what happens in short nearsightedness (myopia) and farsightedness (hypermetropia) you might actually find the topic makes more sense.

[ateenytinybear]

Thanks for the help guys, but here's the problem: I've watched almost every video I can on lens accomodation, but none answer my questions.
I understand that a thicker lens will result in a shorter focal length, and a thinner lens a longer f.length. BUT doesnt the eye require a specific focal length for it to reach the back of the eye? like the length from middle of the lens to the retina?
that can't change. we cant change our eyes to become physically shorter/longer to shorten/lengthen the focal length. so then wHY do you need to change the focal length if the focal length of your eye has to stay the same? aaahhhh :C

nonetheless im still soopr greatful for your advices!! :)

[ateenytinybear]

oooo never mind, i read more articles and i think i got it :D
heres what helped me if anyone needs it:
https://www.sciencelearn.org.nz/system/images/images/000/000/053/embed/Eye-focus-final-3000X2000.jpg?1457566795