What is the focal length of the lens?

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SUMMARY

The focal length of a diverging lens can be calculated using the lens formula 1/di + 1/do = 1/f. In this case, the object distance (do) is 12 cm and the image distance (di) is -4.1 cm, as the image is virtual. Substituting these values into the equation yields a focal length (f) of approximately 3.06 cm. It is crucial to consider the sign convention for virtual images when performing these calculations.

PREREQUISITES
  • Understanding of lens formulas and sign conventions in optics
  • Basic knowledge of virtual and real images
  • Familiarity with the concept of object distance (do) and image distance (di)
  • Ability to perform algebraic manipulations
NEXT STEPS
  • Study the properties of diverging lenses and their applications
  • Learn about sign conventions in optics, particularly for virtual images
  • Explore the derivation of the lens formula and its implications
  • Investigate the differences between converging and diverging lenses
USEFUL FOR

Students studying optics, physics educators, and anyone interested in understanding lens behavior and calculations related to focal lengths.

keemosabi
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Homework Statement


When a diverging lens is held 12 cm above a line of print, as in Figure 26.29, the image is 4.1 cm beneath the lens. What is the focal length of the lens?
26-29fig.gif



Homework Equations


1/di + 1/do = 1/f


The Attempt at a Solution


1/di + 1/do = 1/f
1/4.1 + 1/12 = 1/f
f = 3.0559 cm

What did I do wrong?
 
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The image is virtual, so di is considered to be negative.
 

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