JEE Main & Advanced JEE Main Paper (Held On 11 April 2014)

  • question_answer
    In a compound microscope the focal length of objective lens is 1.2 cm and focal length of eye piece is 3.0 cm. When object is kept at 1.25 cm in front of objective, final image is formed at infinity. Magnifying power of the compound microscope should be:   [JEE Main Online Paper ( Held On 11 Apirl  2014 )

    A) 200        

    B) 100

    C) 400                                        

    D) 150

    Correct Answer: A

    Solution :

                    Given : \[{{f}_{0}}=1.2cm;{{f}_{e}}=3.0cm\] \[{{u}_{0}}=1.25cm;{{M}_{\infty }}=?\] From\[\frac{1}{{{f}_{0}}}=\frac{1}{{{v}_{0}}}-\frac{1}{{{u}_{0}}}\]\[\Rightarrow \]\[\frac{1}{1.2}=\frac{1}{{{v}_{0}}}-\frac{1}{(-1.25)}\] \[\Rightarrow \]\[\frac{1}{{{v}_{0}}}=\frac{1}{1.2}-\frac{1}{1.25}\]\[\Rightarrow \]\[{{v}_{0}}=30cm\] Magnification at infinity,\[{{M}_{\infty }}=-\frac{{{v}_{0}}}{{{u}_{0}}}\times \frac{D}{{{f}_{e}}}\] \[=\frac{30}{1.25}\times \frac{25}{3}\](\[\because D=25cm\]least distance of distinct vision) = 200 Hence the magnifying power of the compound microscope is 200                                


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