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Homework Help: Lenses Question

  1. Mar 1, 2009 #1
    When i'm given do, ho, and hi. How would i solve for di
    Normally i would do -di/do = hi/ho and cross-multiply but i'm not sure how the negative comes into effect.

    do = object distance
    di = image distance
    ho = object height
    hi = image height



    If...

    ho = 3cm
    hi = 4cm
    do = 5cm

    What would be di?

    Thanks
     
  2. jcsd
  3. Mar 1, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Please provide the complete statement of the problem you are trying to solve. (I presume that a negative image height means that the image is inverted.)
     
  4. Mar 1, 2009 #3
    It's just made up values and i want to know how i would solve for di. The negative in the formula confuses me
     
  5. Mar 1, 2009 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Start with:
    -di/do = hi/ho

    You can solve for di by cross-multiplying if you like, or just multiply both sides by -do. As I said before, a negative value for di just means that the image is inverted. (Real images are inverted.)
     
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