Solving Light and Lenses Questions: Focal Length, Magnification, Distance

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SUMMARY

This discussion focuses on solving problems related to lenses, specifically calculating object distance and magnification using the lens formula and magnification equations. The first problem involves a magnifying glass with a focal length of 10 cm, where the postage stamp must be placed 26 cm from the lens to achieve a comfortable viewing distance of 30 cm from the eyes. The second problem presents a lens with a focal length of +20 cm and a magnification of 4, requiring the calculation of the distance between the object and the image using the lens formula.

PREREQUISITES
  • Understanding of the lens formula: 1/f = 1/Do + 1/Di
  • Knowledge of magnification equations: Mag = hi/ho = -Di/Do
  • Familiarity with focal length concepts in optics
  • Basic algebra skills for solving equations
NEXT STEPS
  • Study the derivation and applications of the lens formula in optics
  • Learn about different types of lenses and their properties
  • Explore practical applications of magnification in various fields
  • Investigate the effects of lens curvature on focal length and magnification
USEFUL FOR

Students studying optics, physics educators, and anyone interested in understanding the principles of lenses and magnification calculations.

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Homework Statement


1)A philatelist uses a magnifying glass with a focal length of 10cm. In order to examine a rare postage stamp, he holds the lens 4 cm from his eyes. If the distance for the most comfortable viewing of the image is 30cm from his eyes, how far from the lens must the postage stamp be placed? What will the magnification be?

2)A lens has a focal length of +20cm and a magnification of 4. How far apart are the object and the image?


Homework Equations



1/2) 1/f=1/Do+1/Di
Mag = hi/ho = -Di/Do

The Attempt at a Solution



I don't even know where to begin with the first question. I'm having difficulty interpreting it. Any help would be greatly appreciated.
 
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If the distance for the most comfortable viewing of the image is 30cm from his eyes, and the lens is at 4 cm from the eye, you have to keep the stamp at such distance from the lens that it forms the inage at 30cm - 4 cm = 26 cm from the lens. Now find the object distance.
 

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