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Homework Help: At what distance from the lens is the image

  1. May 19, 2016 #1
    1. The problem statement, all variables and given/known data
    A punctual source of light is in the focal point of a diverging lens. in which distance from the lens is the image. Draw the road of rays.

    2. Relevant equations
    The objects at focal point don't have an image.

    3. The attempt at a solution
    So how should I draw the rays (it says in the problem)?
  2. jcsd
  3. May 20, 2016 #2


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    Gold Member

    My feeling would be to find the position of the image, then draw the ray paths accordingly.

    You can find the image position using a formula, or, perhaps more interestingly, by drawing rays for an off-axis point at the focal distance. (The problem with the focal point being on-axis is that all the standard rays are coincident.)
  4. May 20, 2016 #3


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    Are you sure? Where is the image if the object is very near to the focal point in case of a converging lens?
    What do you know about the focal length of a diverging lens?
    Where is the image if the object distance is do = |f|?
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