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Homework Help: Converging Lens

  1. May 11, 2012 #1
    I have this in my home work and i am not 100% on if i have it right or not

    A converging lens with a focal length of 25 cm is used to make a slide projector. If the image is to be projected onto a screen 10m away, how far should the lens be located from the transparency?

    I did it like this:

    1/s + 1/1000cm = 1/25cm

    solve for s

    1/s = 1/25cm - 1/1000cm
    ∴ s = 25.64cm (2dp)

    Is this right or am i way off. If some one could help would be a big help thanks.
     
  2. jcsd
  3. May 11, 2012 #2
    Or should it be 3.9mm i am a bit lost here i think lol.
     
  4. May 11, 2012 #3

    Doc Al

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    Staff: Mentor

    Looks OK to me.
     
  5. May 11, 2012 #4

    Doc Al

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    Staff: Mentor

    Where did you get that value?
     
  6. May 11, 2012 #5
    I posted this somewhere else and someone posted that but could not see how they got to it :)
     
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