Page 114 - Physics - XII
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C           F            P
                     Image at infi  nity                                  C             F      O      P     I







                               (e) Object at F                          (f) Object between F and P


                                           Fig. 6.1:  Formation of images by a concave mirror



              Principle/Theory

              The position, nature, and the relative size of the image of an object formed by a concave mirror depends
              upon the position of the object with respect to the pole of the mirror. It is shown by the ray diagrams in
              Fig. 6.1.

              Procedure

              1.  Estimate the rough focal length of the mirror.
              2.  Mount concave mirror in the holder in the fi rst upright and place it in the middle of the optical bench.

              3.  Mount the cardboard screen on the second upright and place it at a distance equal to rough focal length
                  of the mirror from fi rst upright.

              4.  Mount the burning candle on the third upright and place it on the other end of the central upright and
                  near the end of the optical bench.

              5.  Adjust the upright carrying candle perpendicular to the scale such that the line joining the pole of the
                  mirror and tip of the candle fl ame is parallel to the length of the optical bench.

              6.  Find out the approximate position of centre of curvature C using the relation R = 2f. C lies at a distance
                  R from the pole of mirror.
              7.  Place the candle upright at a distance so that it lies beyond C (Fig. 6.1b) and adjust the position of the

                  screen and heights of the uprights so that an inverted image of fl ame of burning candle is formed on the
                  screen. Move the screen to make image sharp which is formed between F and C.
              8.  Now, move the candle upright towards the pole of the mirror so that it lies between the focus F and
                  centre of curvature C of the mirror.

              9.  Locate the position of image of the candle fl ame and adjust the position of screen and the height of the
                  screen and candle so that a sharp real inverted image of candle fl ame is obtained on the screen. The
                  real, inverted, and magnifi ed image would be formed beyond C.

              10. Repeat the experiment for diff erent positions of the candle fl ame and observe the position, nature, and
                  size of the image. Note the observations in the observation table.




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