question_answer

Using the data given below, state which two of the given lenses will you prefer to construct a best possible (i) telescope (ii) microscope. Also indicate which of the selected lenses is to be used as an objective and as an eyepiece in each case.      

Lenses	Power (P)	Aperture (A)
\[{{L}_{1}}\]	\[6D\]	\[1cm\]
\[{{L}_{2}}\]	\[3D\]	\[8cm\]
\[{{L}_{3}}\]	\[10D\]	\[1cm\]

          

Answer:

                Focal lengths of the three lenses are \[\text{16}.\text{67}\]\[\text{cm},\text{ 33}.\text{33 cm}\] and \[\text{1}0\text{ cm},\]respectively. (i) For constructing telescope, \[{{L}_{2}}\] should be used as objective because its aperture is largest and \[{{L}_{3}}\] as eyepiece because its focal length is smallest. (ii) For constructing microscope, \[{{L}_{3}}\] should be used as objective and \[{{L}_{1}}\] as eyepiece because both the lenses of microscope should have short focal lengths and the focal length of objective should be smaller than the eyepiece.