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Homework Help: Finding Object Distance and Image Distance

  1. Apr 14, 2012 #1
    1. The problem statement, all variables and given/known data

    More mirrors. Object O stands on the central axis of a spherical or plane mirror. For this situation (Table 34-4 below. All distances are in centimeters.) , find (a) the type of mirror (0 depicts "plane", 1 - "concave", 2 - "convex"), (b) the radius of curvature r (nonzero number or 0 if infinity), (c) the object distance p, (d) the image distance i.

    f= -42
    m= +0.26

    (a) 2
    (b) -84

    3. The attempt at a solution

    So I'm stuck mainly because the focal length (f) is negative. I think since f is less than m the mirror is convex. Would I still solve for p the same way?

    p= (1 - (1/m))*f
    p= 199.538 cm

    and then equals
    i = -mp
    i = -51.8799

    Am I right?
  2. jcsd
  3. Apr 15, 2012 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    There are ways to check your answer to problems like this, which is to see if your solution satisfies the necessary equations.

    So: is it true that
    1/p + 1/i = 1/f​
    or in other words, that
    1/199.5 + 1/(-51.9) = 1/(-42)?​

    p.s. you're correct that a negative f means that the mirror is convex, and you solve using the usual formula that relates p, i, and f.
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