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Homework Help: Convex mirror question how long the image is?

  1. May 11, 2014 #1
    Shiny lawn spheres placed on pedestals are convex mirrors.
    One such sphere has a diameter of 40 cm. A
    12 cm long robin sits in a tree 1.5 m from the sphere.
    (a) Where is the image of the robin?
    (b) How long is the image?

    f=R/2 to find radius
    1/v=1/f-1/u to find image distance (the mirror equation)
    M=v/u magnification and length (maginification equation)

    my answer just not to sure if its right.

    v= -9.4cm

    b) m=v/u
    = -9.4/150
    = 0.06cm

    not to sure if that was the way to go.
  2. jcsd
  3. May 11, 2014 #2


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    I do not understand the line with ?????

    For question b, you gave the magnification, (with wrong sign) instead of the size.

  4. May 11, 2014 #3
    its suppose to be
    1/v=1/f-1/u (trying to find image distance)
    1/v=1/-10 -1/50
    v= -9.4cm

    then with part b i think i use the magnification and multiply it with the height of object to get image size

    0.06 x 12cm= 0.75cm
  5. May 11, 2014 #4


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    Where does 50 come from? The object distance is 150 cm.

    that is correct.
  6. May 11, 2014 #5
    Yes sorry another typo it is 150 i did the calculation with 150 but typed in 50.
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