CATAGORY: Other
QUESTION: The focal length of a double convex lens is 4.0 cm. An object
0.35 cm high is 2.5 cm from the lens. What type of image is formed and
what is its orientation? Calculate its location and size.

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>From the lensmakers equation

(1)  1   1   1
     - = - + -
     f   o   i
     
     Where f = focal length = 4.0cm 
           o = object distance = 2.5cm
           i = image distance = ?
           
solving for i


(2)  1   1   1     1        1
     - = - - - = ------ - ----- = .4cm^-1 - .25cm^-1 = .15 cm^-1 
     i   o   f   2.5cm    4.0cm
     
     thus
           __
(3)  i = 6.66cm ~ 6.7cm

the image height h(i)is given in terms of the object height h(o)

(4)   h(o)       h(i)
      ----  = -  ----
       o          i
       
Thus
                 h(o)
      h(i) = - i ----
                  o
                       0.35 cm 
            = - 6.7cm  -------                  
                        2.5cm   
           
            = -.94cm

The image is 6.7cm behind the lens (opposite side of the object).  It
is a real it is INVERTED (because of the minus sign) and is .94cm in
height.

          ********************
          *                  *
          *  i = 6.7cm       *
          *                  *
          *  h(i) = -.94cm   *
          *                  *
          ********************