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Optics - For what distance must we focus our eyes to see this image

  1. Nov 17, 2008 #1
    An object is placed 1m in front of a plane mirror. An observer stands 3m behind the object. For what distance must the observer focus his eyes in order to see the image of the object?
     
  2. jcsd
  3. Nov 18, 2008 #2

    Mentallic

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    Re: Reflection

    5 metres? Was that all there is to the question?
     
  4. Nov 18, 2008 #3
    Re: Reflection

    Yeah that is all the question was. How did you figure that out?
     
  5. Nov 18, 2008 #4

    tiny-tim

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    Hi Kathi!

    Hint: for a plane mirror, where is the image in relation to the object? :smile:

    (Hi Mentallic: please don't give out answers! :wink:)
     
  6. Nov 18, 2008 #5
    Re: Reflection

    Do you mean that it is in an angle? I am not quite sure of the answer you are looking for
     
  7. Nov 18, 2008 #6

    tiny-tim

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    Mirrors are like lenses … every object has an image.

    For a plane mirror, where is the image of an object? :smile:
     
  8. Nov 18, 2008 #7
    Re: Reflection

    The image is located in front of the mirror. Isn't the image distance equal to the object distance. Thus it would be 3m
     
  9. Nov 18, 2008 #8
    Re: Reflection

    Ok so now that I am thinking about, is the image behind the mirror or in front. I am starting to think it is behind?
     
  10. Nov 18, 2008 #9

    tiny-tim

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    Yup, the image is definitely behind the mirror! :biggrin:

    (It's a virtual image: the rays of light "from" it don't actually get anywhere near it, do they? :smile:)

    Sooo … how far away from the observer is the image of that object she's standing behind?​
     
  11. Nov 18, 2008 #10
    Re: Reflection

    The object is 1m away and the person is 3m away so it would be 3m +1m + the 1m behind the mirror so it would be 5m.
     
  12. Nov 18, 2008 #11

    tiny-tim

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    That's it!

    Any questions? :smile:
     
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