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STUDY OF COMBINATION OF FOCAL LENGTH

Aim :       To obtain a lens combination with the specified focal length by using two lenses from the given set of lenses.

Apparatus : Convex and concave lenses of different focal lengths but of same apparature, scale, screen.

Procedure :

      Choose any two lenses from the given set. Make its combination by keeping them close to each other.

      Check whether, the combination is convex or concave by observing image through it.

      If it is concave combination, choose another set.

      If it is convex combination, obtain the image of distant object on the screen. Measure the distance between lens combination and screen, which is the focal length of combination. If the focal length is of the specified value, then that is the required set of lenses.

      If focal length is not of the specified value, repeat the procedure till you obtain the specified focal length.

Conclusion :

            Specified focal length of combination                              =…………… cm

           Observed focal length of combination                              =…………… cm

          The type of lenses used in the combination are                  =……… cm and …… cm

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