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Homework Help: Apparent distance of object in planar mirror

  1. Jul 12, 2007 #1
    Tanya is sitting in an optometrist’s chair, facing a mirror that is 2.25 m from her eyes. It the eye chart she is looking at is hanging a wall behind her head, 1.75 m behind her eyes. How far from her eyes does the chart appear to be?

    Would the answer be 4 m? (2.25 m +1.75 m)... I'm assuming it's a plane mirror
     
  2. jcsd
  3. Jul 12, 2007 #2

    Chi Meson

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    Yes, it's this simple.

    Do you need to provide any proof of your answer?
     
  4. Jul 12, 2007 #3
    Yeah.... can i explain in words, that since it's a plane mirror, etc.
     
  5. Jul 12, 2007 #4
    BTW, is it possible for you to help me with a few other physics (optics) questions??? I'm really really confused..
     
  6. Jul 12, 2007 #5

    Kurdt

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    Would it not be 6.25m? :confused:
     
  7. Jul 12, 2007 #6

    Kurdt

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    Feel free to post any physics homework related questions in this forum.
     
  8. Jul 12, 2007 #7

    Chi Meson

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    Whoops, yes it s. I didn't read the question closely.

    Leehom: How far is the chart from the mirror?
     
  9. Jul 12, 2007 #8
    I'm sorry I don't understand where the 6.25 m came from... can you pls. explain?
     
  10. Jul 12, 2007 #9

    Chi Meson

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    Read the question and tell me: how far is the chart from the mirror?
     
  11. Jul 12, 2007 #10
    And why would charts used for this purpose have to be specially made?
     
  12. Jul 12, 2007 #11

    I think I get it now... 2.25 m + 2.25 m + 1.75 m = 6.25 m...
     
  13. Jul 12, 2007 #12

    Chi Meson

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    If you don't answer my question, I'm leaving.

    Edit:

    Phew! Just in time!
     
  14. Jul 12, 2007 #13

    Kurdt

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    Why do you think charts would have to be specially made?
     
  15. Jul 12, 2007 #14

    Chi Meson

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    Is this one of the questions? All optometrist's charts are "specially made."
     
  16. Jul 12, 2007 #15
    well... i wrote that the letters would have to "reversed" so that they would appear upright in the mirror according to prop. of images formed by a plane mirror...

    and another quick verification on this question:
    Light is shining on to a plane mirror at an angle of incidence of 27 deg. If the plain mirror is tilted such that the angle of incidence is reduce by 8 deg, what will be the total change in the angel of reflection from the original reflected light?

    Would the change be 8 deg due to law of reflection? since the angle of reflection is calculated from the normal
     
  17. Jul 12, 2007 #16

    Chi Meson

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    If you tilt the mirror, you tilt the normal. That means both the incident angle and the reflected angle increase by 8 degrees.
     
  18. Jul 12, 2007 #17
    But the question specifically states that the incident angle is reduced by 8 deg
     
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