The Use Of Lenses in Optical Dvices

 The Differences between Microscope and Telescope
                  The Compound Microscope

           

  -We use it to view very small objects.

  -Microscope consists of two convex lenses:

      a)The objective 

     -the lens which is nearest to object.

     -a powerful convex lens with a short focal length.

     -focal length of the objective is fo.

      b)Eyepiece

     -the lens which is nearest to the eye.

     -eyepiece has a longer focal length than the objective.

     -focal length of the eyepiece is fe.

                          The Telescope

                                        

 

    -Astronomical telescope consists of two convex lenses:

        a)The objective.

        b)The eyepiece.

    -The objective is a convex lens with a wide aperture and long focal length to  enable the telescope collect as much light as possible. 

    -Eyepiece is a convex lens of short focal length.

    -The picture shows three actual rays coming from the top of a distant object.Since the object is far away,the rays are assumed to be parallel when incident on objective lens.

    -The rays at point I will emerge parallel from the eyepiece and appear to come from the top of final image at infinity.

    -The total distance between the objective and the eyepiece is = fo+fe

    -The magnifying power of the telescope :

                     M=fo/fe

    -If the power of eyepiece is increasing,the power of objective is reducing,it can give a high magnification.