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Mirror word problem

  1. Apr 28, 2008 #1

    ~christina~

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    1. The problem statement, all variables and given/known data
    (a) On a sunny afternoon in April, three physics students took a mirror and a screen to the roof of a building. They selected a distant building, and while one student held the mirror a second one adjusted the distance between the screen and the mirror in an attempt to form a clear image of the building on the screen. Once the clear sharp image was formed on the screen, the third student made a measurement several times, took the average of these measurements, and then concluded that the focal length of the mirror is 17.5 cm.
    (i) Describe the measurement made and explain how this measurement gives the focal length of the mirror.
    (ii) What type of mirror did the students take to the roof?
    (iii)Was the image on the screen real or virtual?; upright or inverted?; enlarged or reduced?

    (b) Upon returning to the classroom, the students placed the mirror on an optical bench. An object was placed 22 cm in front of the mirror. Is an image formed on the screen for this object distance? If no, explain. If yes, find the characteristics (that is, the location, orientation, magnification, etc.) of the image formed.

    2. Relevant equations

    3. The attempt at a solution
    (i) Describe the measurement made and explain how this measurement gives the focal length of the mirror.

    (ii) What type of mirror did the students take to the roof?
    I say it's a concave mirror.

    (iii)Was the image on the screen real or virtual?; upright or inverted?; enlarged or reduced?

    It's inverted, and reduced as well. and the image is a real image.

    Are my ideas right?

    Thanks
     
  2. jcsd
  3. Apr 28, 2008 #2

    ~christina~

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    Gold Member

    I was thinking that the reason that they could make an average measurement was that the building was an infinately far distance away and thus the focal point was also the point that the image was able to be seen on the screen at.

    And that the image could not have been viewed with a convex mirror or a flat mirror as well but only with a concave mirror because that is the only mirror which would allow the light rays to converge on one point which would allow for the image to be reflected onto the screen. (not only that, the focal length is possitive and so it couldn't be a convex mirror in the first place)

    right or no?

    Thank you
     
  4. Apr 28, 2008 #3
    The fact that a real image is projected onto the screen in part 1 suggests you have a concave mirror.

    When an object is placed outside the focal length of the mirror in part 2, the image is real, inverted, and diminished.
     
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