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Homework Help: Geometric optics question.

  1. Feb 22, 2012 #1
    Problem 1

    A flat screen TV is place on a wall in a room. A lens of focal length 50cm is placed between the television and the opposite wall so that a sharp image with one quarter of that of the area of the television is produced on the opposite wall.


    Magnification = [itex]\frac{Image}{Object}[/itex]

    M = [itex]\frac{V}{U}[/itex]

    M = [itex]\frac{1}{4}[/itex]

    V = [itex]\frac{U}{4}[/itex]

    [itex]\frac{1}{f}[/itex] = [itex]\frac{1}{U}[/itex] + [itex]\frac{1}{V}[/itex]

    [itex]\frac{1}{50}[/itex] = [itex]\frac{1}{U}[/itex] + [itex]\frac{4}{U}[/itex] (From above)

    [itex]\frac{1}{50}[/itex] = [itex]\frac{5}{U}[/itex]

    U = 250 cm

    U = 0.25 cm

    Is this right?
  2. jcsd
  3. Feb 22, 2012 #2
    The magnification given by m=v/u is a LINEAR magnification.... this is how much lengths are magnified. If m = 2 it means lengths are 2x greater..... what will that mean for AREA magnification?
    Hope this helps
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