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Focal length of a convex mirror

  1. Jul 16, 2013 #1
    1. The problem statement, all variables and given/known data

    An object is 12.0 cm in front of a convex mirror. When the convex mirror is replaced
    with a flat mirror, the image distance is 5.0 cm farther away from the mirror. What is the
    focal length of the convex mirror?

    2. Relevant equations

    f=-1/2R

    1/do+1/di=1/f

    3. The attempt at a solution

    (1/0.12m)+1/di=1/f
    ?

    12+5cm=17cm=0.17m

    (1/0.17m)+1/di=1/f
    ?
     
  2. jcsd
  3. Jul 17, 2013 #2

    ehild

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    How is the image distance related to the object distance in case of a flat mirror?


    ehild
     
  4. Jul 17, 2013 #3
    They would be equidistant to the mirror?
     
  5. Jul 17, 2013 #4

    ehild

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    Yes. So the mirror image in case of flat mirror is farther away by 5 cm than the image produced by the convex mirror. If the object distance is 12 cm and the image distance is shorter by 5 cm, what can be di?

    ehild
     
  6. Jul 17, 2013 #5
    di=12cm for the flat mirror
    di=7cm for the convex mirror?
     
  7. Jul 17, 2013 #6
    Using the above di, I got f=0.12m.
     
  8. Jul 17, 2013 #7
    The image is behind the mirror.
     
  9. Jul 17, 2013 #8

    ehild

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    The image is at 7 cm distance from the mirror, but the mirror is convex, is the image virtual or real?
    What is the sign of di ?


    ehild
     
  10. Jul 17, 2013 #9

    PeterO

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    Have you solved the problem? A quick ray Trace will do it for you.
     
  11. Jul 18, 2013 #10
    The problem statement tells us that the image is behind the mirror.
     
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