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Does the focal length of a concave lens change in a different medium?

  1. Jul 22, 2012 #1
    My question is as follows:

    Does the focal length of a concave lens change when put into a medium such as water?
    Initially the focal length of the lens is 20 cm in air. Would it get larger or small in water?
     
  2. jcsd
  3. Jul 22, 2012 #2

    tiny-tim

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    Hi Clyner791! :wink:

    Tell us what you think, and then we'll comment! :smile:
     
  4. Jul 22, 2012 #3
    I think the focal length will get larger. My reason for thinking this is because light rays diverge less in a more viscous medium? (I.e. they refract less?).
     
  5. Jul 22, 2012 #4

    tiny-tim

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    you'll need to explain it a lot better than that …

    where is the image? where do the rays go?

    what difference does it make whether it's concave or convex?​
     
  6. Jul 22, 2012 #5
    In air: an object is placed 50 cm from the lens (concave) with a focal length 20cm. This produces an image 33.33 cm from the lens (again in air)

    So, what change (if any) will occur to the focal length of the lens
     
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