1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Diverging lens on filament

  1. Aug 28, 2009 #1
    1. The problem statement, all variables and given/known data
    A diverging lens with focus 5 cm is placed on a filament. Find the distance between the lens and the filament


    2. Relevant equations
    [tex]\frac{1}{f}=\frac{1}{di}+\frac{1}{d}[/tex]


    3. The attempt at a solution
    Focus of diverging lens is negative so, f = -5 cm. I think the question is asking about di. What is d ? Can it be infinity because the filament gives light until far enough distance ?

    Thanks
     
    Last edited: Aug 28, 2009
  2. jcsd
  3. Aug 28, 2009 #2

    Maroc

    User Avatar
    Gold Member

    From what i recall di = initial distance of object and d is the final. However, to solve your question i won't be as much as of a help as others. Sorry.
     
  4. Aug 28, 2009 #3
    Hi Maroc

    Ah thanks for clarifying my equation. I usually use d as distance of object and d' as distance of the image. I think it's better to use your notation.

    Thanks :)
     
  5. Aug 28, 2009 #4

    Maroc

    User Avatar
    Gold Member

    No problem songoku,

    Just like to help around. If there is no help here try wiki or other info sites regarding this matter.
     
  6. Aug 28, 2009 #5

    rl.bhat

    User Avatar
    Homework Helper

    If you real positive sign convention,
    the equation becomes
    -1/f = 1/do + 1/di, where do is the object distance and di is the image distance.
    Here do = f = 5 cm
     
  7. Aug 28, 2009 #6
    Hi Mr. rl.bhat

    Why does do = 5 cm ? Based on your equation, I think the question is asking about do, the distance between the lens and filament.

    Thanks
     
  8. Aug 28, 2009 #7

    Maroc

    User Avatar
    Gold Member

    he rearranged the equation to get 5cm
     
  9. Aug 28, 2009 #8
    Hi Maroc

    Oh I see. So like I said, di (the distance of image) = infinity, right ?

    Thanks
     
  10. Aug 28, 2009 #9

    rl.bhat

    User Avatar
    Homework Helper

    In the given problem there are two unknowns. By a diverging lens you cannot get an image at infinity. So I thought the object is at the focus of the diverging lens. In the MCQ most of the students will select the image at infinity, which is wrong.
     
  11. Aug 28, 2009 #10
    Hi Mr. rl.bhat

    Oh I see. The image of diverging lens should be located between the focus and the center of the lens.
    But I don't understand why you thought the object is at the focus. I think it's possible the object (in this case I suppose the object is the filament) is located between f and 2f or further than 2f and the question is asking about this distance.

    Thanks
     
  12. Aug 29, 2009 #11

    ideasrule

    User Avatar
    Homework Helper

    I'm confused. The question says that the lens is placed on the filament, then asks for the distance between the lens and the filament? If one is on top of the other, wouldn't the distance be 0?
     
  13. Aug 29, 2009 #12
    Hi ideasrule

    I'm not sure about that, but that's the question. Or maybe the lens is placed in front of a filament in a lightbulb?

    Thanks
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Diverging lens on filament
  1. Diverging Lens (Replies: 4)

  2. Diverging lens (Replies: 6)

  3. Diverging Lens (Replies: 1)

  4. Diverging Lens (Replies: 6)

Loading...