How Do You Calculate Object Distance in Lens Equations?

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SUMMARY

The discussion centers on calculating object distance using the lens formula for a converging lens with a focal length of 56.0 mm and an image distance of 68.0 mm. The correct formula is 1/f = 1/di + 1/do, where di is the distance of the image from the lens. The user initially miscalculated by incorrectly adding the image distance to the focal length, leading to an incorrect object distance of 102.04 mm. The correct approach requires careful attention to the signs and values in the lens equation.

PREREQUISITES
  • Understanding of the lens formula: 1/f = 1/di + 1/do
  • Knowledge of converging lens properties
  • Basic algebra skills for solving equations
  • Familiarity with the concept of image distance and object distance
NEXT STEPS
  • Review the lens formula derivations and applications
  • Practice problems involving different focal lengths and image distances
  • Explore the effects of lens curvature on image formation
  • Learn about real vs. virtual images in optical systems
USEFUL FOR

Students studying optics, physics educators, and anyone interested in understanding lens equations and image formation principles.

sp1974
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The homework problem is "A sharp image is located 68.0 mm behind a 56.0 mm focal length converging lens. Calculate the object distance in millimeters"



1/f = 1/di + 1/do



I tried solving based on having focal (f) and distance of image (di) so 1/56 mm = 1/(68 mm + 56 mm) + 1/do
I solved for do coming up with 102.04 mm and the computer doesn't accept
 
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Why is di=68+56?
 
I figured because the focal point was 56 and it says 68 behind it so I thought it would be f distance + the 68
 
It states it is behind a 56mm focal length lens. Not 68mm behind the focal length of a 56mm focal length lens.
 
I also did it as 1/56 = 1/68 + 1/do and the computer didnt accept that on as well
 
ok I figured this one out. I had my numbers flip flopped my numbers when subtracting
 

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