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Homework Help: Distance of object/lens

  1. May 1, 2010 #1
    The homework problem is "A sharp image is located 68.0 mm behind a 56.0 mm focal length converging lens. Calculate the object distance in millimeters"



    1/f = 1/di + 1/do



    I tried solving based on having focal (f) and distance of image (di) so 1/56 mm = 1/(68 mm + 56 mm) + 1/do
    I solved for do coming up with 102.04 mm and the computer doesn't accept
     
    Last edited: May 1, 2010
  2. jcsd
  3. May 1, 2010 #2
    Why is di=68+56?
     
  4. May 1, 2010 #3
    I figured because the focal point was 56 and it says 68 behind it so I thought it would be f distance + the 68
     
  5. May 1, 2010 #4
    It states it is behind a 56mm focal length lens. Not 68mm behind the focal length of a 56mm focal length lens.
     
  6. May 1, 2010 #5
    I also did it as 1/56 = 1/68 + 1/do and the computer didnt accept that on as well
     
  7. May 2, 2010 #6
    ok I figured this one out. I had my numbers flip flopped my numbers when subtracting
     
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