Understanding Concave Lenses: A Homework Statement

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SUMMARY

The discussion centers on the application of the lens maker's equation to concave lenses, specifically in a homework context. The user calculated the radius of curvature as 16 cm and the focal length in water as -81.8 cm, confirming the negative focal length characteristic of concave lenses. The user also derived the image distance (s') as -37.73 cm and explored the implications of object placement relative to the focal length. Ultimately, the user resolved their confusion regarding the ray diagram and image positioning.

PREREQUISITES
  • Understanding of the lens maker's equation
  • Knowledge of focal lengths and their signs in optics
  • Familiarity with ray diagrams for concave lenses
  • Basic concepts of magnification in optics
NEXT STEPS
  • Study the lens maker's equation in detail
  • Learn about the properties of concave lenses and their applications
  • Explore ray diagram construction for various lens types
  • Investigate the relationship between object distance, image distance, and magnification
USEFUL FOR

Students studying optics, physics educators, and anyone seeking to deepen their understanding of lens behavior and image formation.

indie452
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Homework Statement



the question is attached


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The Attempt at a Solution



ok so a and b i can do but c), i donts know whether my answer is right and I am a little confused about the conceptual idea...

so first thing i did was found the radius of curvature using the lens maker equ using the original setup in air...this i found to be 16cm... [note r1 = -r2]

next i found the focal length in the water situation (i know it doesn't ask for it but still)...this i found to be -81.8cm...
this confuses me cause i thought that only concave lens had negative focal lengths and this is a concave lens...also can the focal length be greater than the radius in a lens? i think it can but can't find anywhere that confirms this...

now to find the image distance s' ... 1/f = 1/s + 1/s'

i got s' = -37.73cm

then magnification i can do but is what I've done ok?
also can you have a diverging lens that is concave if the object is infront of the focal length? cause that is the only reason that i can think for the focal length to be negative...
 
Last edited:
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ok i just drew the ray diagram and my image was on the same side as the object which agrees with the negative sign for the s'...but the image is further away than the focal point

see attached
 

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  • rr4.jpg
    rr4.jpg
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ive figured it out so no need to answer
 

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