JCECE Medical JCECE Medical Solved Paper-2015

  • question_answer  A plano-convex glass lens \[({{\mu }_{g}}=3/2)\] of radius of curvature \[R=20\text{ }cm\]is placed at a distance a from a concave lens of focal length 40 cm. What should be the distance b of a point object O from plano-convex lens so that the position of final image is independent of a?

    A)  20 cm         

    B)  60 cm

    C)  40 cm           

    D)  30 cm

    Correct Answer: C

    Solution :

     Focal length of the plano-convex lens is \[\frac{1}{f}=({{\mu }_{0}}-1)\left( \frac{1}{20}-\frac{1}{\infty } \right)\] \[=\left( \frac{3}{2}-1 \right)\left( \frac{1}{20} \right)=\frac{1}{2}\times \frac{1}{20}\] \[\Rightarrow \] \[t=40\,cm\] If point object O is placed at a distance of 40 cm from the plano-convex lens, rays become parallel and final image is formed at second focus or 40 cm from concave lens which is independent of a.


You need to login to perform this action.
You will be redirected in 3 sec spinner