Physics Help Forum Finding optical power of corrective lenses?
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 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 -I
 May 23rd 2019, 05:34 AM #2 Senior Member     Join Date: Jun 2016 Location: England Posts: 890 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 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. __________________ ~\o/~ Last edited by Woody; May 23rd 2019 at 05:44 AM.
 May 24th 2019, 07:59 PM #3 Junior Member   Join Date: May 2019 Posts: 1 Notations Hi, di means image distance do menas object distance Peye means Power from the eye

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