Go Back   Physics Help Forum > High School and Pre-University Physics Help > Light and Optics

Light and Optics Light and Optics Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old Jun 29th 2009, 06:37 AM   #1
Member
 
Join Date: Jun 2009
Posts: 79
Correction of defects in vision

Q) The diameter of an eyeball of a certain person is 24mm,but the normal diameter of an eyeball should be 23mm.
What is the power of the lens to be used inorder to correct this defect?

He seems to be having a larger eye than normal...
so the image formed of an object would in this case be at 23mm,from the eyelens,which, would mean that he would have to use a diverging lens to correct this defect,to form an image at 24mm.

As for trying to find the focal length of the correction lens,I have no idea how to do it.
I know that,
1/f = 1/v - 1/u , and that power = 1/f,
but I can't figure out what values need to be substituted.

Thanks in advance
hana1 is offline   Reply With Quote
Old Jun 29th 2009, 06:24 PM   #2
Senior Member
 
Join Date: Dec 2008
Location: Udupi, Karnataka, India
Posts: 292
You can take the object at infinity.
Then use the formula 1/f1 + 1/f2 = 1/F
Here f1 is the focal length of the normal eye and F is the focal length of defective eye. And f2 is the focal length of the correcting lens.
sa-ri-ga-ma is offline   Reply With Quote
Old Jun 29th 2009, 11:37 PM   #3
Member
 
Join Date: Jun 2009
Posts: 79
Originally Posted by sa-ri-ga-ma View Post
You can take the object at infinity.
Then use the formula 1/f1 + 1/f2 = 1/F
Here f1 is the focal length of the normal eye and F is the focal length of defective eye. And f2 is the focal length of the correcting lens.
So taking the object at infinity,for the defective eye,and applying sign convention(taking the distances measured in the direction of the rays from the object as negative,while those measured in the direction opposite to the rays as positive),

1/F = -1/2.3 - 1/infinity
1/F = -1/2.3cm = -0.435cm

taking the object at infinity,for the normal eye,
1/f1 = -1/2.4 - 1/infinity
1/f1 = -0.417cm

Then using the formula suggested,
1/f2 = 1/F - 1/f1
1/f2 = -0.435 -(-0.417)
I get f2 = -55.56cm,
since the focal length is negative ,wouldn't the correcting lens be a converging lens?
hana1 is offline   Reply With Quote
Old Jun 30th 2009, 04:11 AM   #4
Senior Member
 
Join Date: Dec 2008
Location: Udupi, Karnataka, India
Posts: 292
Originally Posted by hana1 View Post
So taking the object at infinity,for the defective eye,and applying sign convention(taking the distances measured in the direction of the rays from the object as negative,while those measured in the direction opposite to the rays as positive),

1/F = -1/2.3 - 1/infinity
1/F = -1/2.3cm = -0.435cm

taking the object at infinity,for the normal eye,
1/f1 = -1/2.4 - 1/infinity
1/f1 = -0.417cm

Then using the formula suggested,
1/f2 = 1/F - 1/f1
1/f2 = -0.435 -(-0.417)
I get f2 = -55.56cm,
since the focal length is negative ,wouldn't the correcting lens be a converging lens?
No. It is not correct.
For normal eye focal length of the eye lens is 2.3 cm. You have to increase it to 2.4 cm for the defective eye by keeping a diverging lens of focal length f2 in front of the eye lens. Find the value of f2.
sa-ri-ga-ma is offline   Reply With Quote
Old Jun 30th 2009, 06:48 AM   #5
Member
 
Join Date: Jun 2009
Posts: 79
Thank you so much,sir.
No. It is not correct.
For normal eye focal length of the eye lens is 2.3 cm. You have to increase it to 2.4 cm for the defective eye by keeping a diverging lens of focal length f2 in front of the eye lens. Find the value of f2.
Yes,I've made another careless mistake.Thanks for pointing it out.

correction : 1/f2 = 1/F - 1/f1
= -1/2.4 - (-1/2.3)
f2= 55.56cm
and P= 1.8D
I hope it's correct now?

Last edited by hana1; Jun 30th 2009 at 07:33 AM.
hana1 is offline   Reply With Quote
Old Jan 23rd 2011, 11:03 AM   #6
Junior Member
 
Join Date: Jan 2011
Posts: 1
Hello evrybody.
Here what i found -> vision correction
tarapozan is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Light and Optics

Tags
correction, defects, vision



Search tags for this page
Click on a term to search for related topics.
Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Short sightedness and correction arze Light and Optics 1 Jul 6th 2009 06:30 PM
Correction of defects in vision 2 hana1 Light and Optics 10 Jul 3rd 2009 04:51 AM
measurement correction and uncertainty of temperature urh Thermodynamics and Fluid Mechanics 0 May 31st 2009 10:09 AM
vision perception starryeyedevil Advanced Optics 1 Apr 19th 2009 10:49 AM


Facebook Twitter Google+ RSS Feed