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1. A concave mirror forms a real image at 25cm from he mirror surface along the principal axis. If the corresponding object is at a 10cm distance, what is the mirror's focal length?

2. A woman looking in a makeup mirror sees her face at twice its actual size and right-side up. If she is 28cm from the mirror, what is its focal length?

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2 answers

  1. 1. Learn the formula
    1/Do + 1/Di = 1/f
    Then use it.

    In this case Do = object distance = 10 cm
    Di = image distance = 25 cm.
    Solve for f

    2. Do = 28
    Di = -56
    The magnification is 2 = |Di/Do|
    Di is negative for an upright image.
    Solve for f
    Use the same equation as part 1 to solve for f.

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  2. 1. 14.2

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