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Homework Help: Lenses Question

  1. Mar 4, 2007 #1
    1. The problem statement, all variables and given/known data
    "A certain lens focuses an object 2.85 m away as an image 48.3 cm on the other side of the lens. What type of lens is it and what is its focal length? Is the image real or virtual?

    2. Relevant equations
    1/f = 1/do + 1/di

    3. The attempt at a solution
    I'm guessing it's a converging lens since the image is on the other side. Diverging lenses create images on the side that light is coming from? Correct?

    Attempt at finding focal length:

    Since the image is coming from where light is not, that's a -1/di, the object is from where the light is coming from so it's +1/do and since it's a congering lens it's +1/f.

    di = 48.3 cm = 0.483 m

    1/f = 1/do - 1/di

    f = 1 / (1/do - 1/di)

    f = (1/2.85 - 1/0.483)^-1 = -0.582 m

    The image has to be real since it will be shown upside down?
  2. jcsd
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