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Homework Help: Convex mirror homework

  1. Nov 15, 2009 #1
    1. The problem statement, all variables and given/known data
    At an intersection of hospital hallways, a convex mirror is mounted high on a wall to help people avoid collisions. The mirror has a radius of curvature of 0.510 m.
    -What is the image distance for a patient 11.9 m from the mirror? (Use the correct sign conventions.)
    -Determine the magnification.

    radius of curvature(R)=-0.51m, so the focal length(f)=-0.255m
    (negative because the mirror is convex)

    object distance(p)=-11.9m

    image distance(q)= ?

    2. Relevant equations
    1/p + 1/q = 1/f or 1/q = 1/f - 1/p

    M = -(q/p)

    3. The attempt at a solution
    1/q = 1/(-0.255) - 1/(-11.9)
    1/q = -1/0.255 + 1/11.9 = -1370/357

    q/1 = -357/1370 = -0.2605839 => q = -0.26m

    This problem was for a web assignment. I had 5 chances to get the right answer but I used most of them up by using f = 0.225 (+and -) instead of f= -0.255. The feed back for q = -0.26 was that it was close to the correct answer and probably off due to a rounding error. I double checked my calculations but I came up with the same answer. I tried
    M = -(q/p) = -(-0.2605839/-11.9) = -0.02198781
    which was the incorrect sign. When I submitted M = +0.02198781 I got the same response as I did for the first answer. I'm sure once I get the right answer for q my answer for M will be fixed, but I don't know where to go from here
  2. jcsd
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