Find Focal Length of Lens When Moving From 20cm to 15cm

AI Thread Summary
When a lens is moved from 20cm to 15cm towards an object, the magnification remains unchanged, prompting the question of the lens's focal length. Participants emphasize the importance of applying relevant equations related to distance, magnification, and focal length. New users are encouraged to demonstrate their understanding before seeking assistance. The discussion highlights the community's guidelines on providing help with homework problems. Overall, the focus is on understanding the relationship between lens position and focal length.
Euler_Euclid
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If a lens is moved towards the object from a distance of 20cm to 15cm, the magnification of the image remains the same. What is the focal length of the lens?

Sorry I am new here so please forgive me if I have violated any rules.:cry:
 
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Welcome to PF!

Euler_Euclid said:
If a lens is moved towards the object from a distance of 20cm to 15cm, the magnification of the image remains the same. What is the focal length of the lens?

Hi Euler_Euclid! Welcome to PF! :smile:

Hint: what equations do you know that apply to distance, magnification, and focal length? :wink:
 


Can you please help me a little more?
 
Euler_Euclid said:
Can you please help me a little more?

oh come on …

you must know some equation about lenses … :smile:
 


Euler_Euclid said:
Sorry I am new here so please forgive me if I have violated any rules.:cry:

FYI:

On helping with questions: Any and all assistance given to homework assignments or textbook style exercises should be given only after the questioner has shown some effort in solving the problem. If no attempt is made then the questioner should be asked to provide one before any assistance is given. Under no circumstances should complete solutions be provided to a questioner, whether or not an attempt has been made.

More at https://www.physicsforums.com/showthread.php?t=5374
 


OK Sorry. I got it now!

Thanks.
 

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