Find the change in focal length

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SUMMARY

The discussion centers on calculating the change in focal length for a nearsighted person using a lens with a -1D prescription. The formula used is the lens formula (1/f) = (1/do) + (1/di), where f represents the focal length, do is the object distance, and di is the image distance. The solution indicates that the focal length of the lens is -0.23 meters, and the user is advised to consider the combination of the eye and glasses to determine the effective focal length. The final calculated near point with glasses is approximately 0.2987 meters.

PREREQUISITES
  • Understanding of lens formulas, specifically (1/f) = (1/do) + (1/di)
  • Knowledge of optical concepts such as focal length and image distance
  • Familiarity with nearsightedness and corrective lenses
  • Basic algebra skills for manipulating equations
NEXT STEPS
  • Study the principles of optics, focusing on lens combinations and their effects on focal length
  • Learn about the eye's anatomy and how it interacts with corrective lenses
  • Explore practical applications of lens formulas in real-world scenarios
  • Investigate different types of lenses and their specific prescriptions
USEFUL FOR

Students studying optics, optometrists, and anyone interested in understanding the effects of corrective lenses on vision.

lha08
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Homework Statement


A nearsighted person has eyeglasses with a -1D prescription. If the near point is at 23 cm without eyeglasses, where is it when they are put on?



Homework Equations


(1/f)=(1/do)+(1/di)


The Attempt at a Solution


I got the answer which is 0.298701298 meters by -1= (1/do)-(1/0.23)...but the problem is that i don't know why it's like that...Any ideas would be extremely helpful! Thanks!
 
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You have that equation wrong,
f = the focal length of the lens ( -0.23m)
di is the image distance (which you don't know - but can assume is the same )
do is the object distance

Then you need the formula for a combination of two lenses (ie the eye + glasses) to find the change in focal length.
 

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