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

Light and Optics Light and Optics Physics Help Forum

Like Tree1Likes
  • 1 Post By Woody
LinkBack Thread Tools Display Modes
Old May 21st 2019, 11:10 PM   #1
Junior Member
Join Date: Apr 2019
Posts: 23
Finding optical power of corrective lenses?

The question is as follows:
"A person with presbyopia has a near point of 40 cm. This person wears glasses to correct their vision such that they can comfortably read the screen of their mobile phone when it is held 25 cm from their eyes.

If this person wears their glasses such that they sit 1.2 cm from their eye, what is the optical power of the corrective lenses in their glasses? (to 2 s.f and in D)"

I am using Peye = 1/di + 1/do

and thus

Peye = 1/0.230 + 1/-0.388

this = 1.77 => 1.8D, which isn't correct.
I subtracted the retina-lens distance from both di and do to get my values. I have been doing a bunch of these questions and surprise I've got them all wrong. Could anyone help me?

Thank you

astupidummydumstupid is offline   Reply With Quote
Old May 23rd 2019, 05:34 AM   #2
Senior Member
Woody's Avatar
Join Date: Jun 2016
Location: England
Posts: 959
Don't assume that the notation you use will always be familiar to everyone.
A lot of the notation we use is just what was chosen (pretty much at random) by the first person to consider the problem.
Sometimes this notation becomes adopted by enough people to become a standard convention,
but this should not be assumed.
It may be that the notation you are using is particular to your tutor, or text book.

Thus in your initial post:
What is the definition of di, do, Peye ?

As an aside have a quick glance at this Wikipedia article <Wikipedia : Light Speed Notation>
Here it explains that even (arguably) the most famous symbol "c" for the speed of light is not completely universally uniquely defined.
topsquark likes this.

Last edited by Woody; May 23rd 2019 at 05:44 AM.
Woody is offline   Reply With Quote
Old May 24th 2019, 07:59 PM   #3
Junior Member
Join Date: May 2019
Posts: 1


di means image distance
do menas object distance
Peye means Power from the eye
jje9046 is offline   Reply With Quote

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

corrective, finding, lenses, optical, power

Thread Tools
Display Modes

Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Finding the power used to change phase? astupidummydumstupid Thermodynamics and Fluid Mechanics 3 Apr 16th 2019 02:27 AM
Lenses system Clyner82 Advanced Optics 1 Sep 26th 2016 03:21 AM
Lenses cyt91 Light and Optics 6 Jun 19th 2010 08:18 AM
Which of the glass lenses above... jenshu Light and Optics 1 Feb 22nd 2010 04:59 AM

Facebook Twitter Google+ RSS Feed