question_answer

A convex lens of focal length \[20\text{ }cm\]is placed in front of a plane mirror at \[20\text{ }cm\] A point object 'O' is placed at \[30\text{ }cm\]towards left from convex lens as shown. The position of final image is

A) Virtual at infinity 

B)                                   Real at infinity

C) Virtual at 20 cm towards left of convex lens          

D) Real at 10 cm towards left of lens.

Correct Answer: D

Solution :

[d] Refraction from lens for \[{{I}_{1}}\] \[\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\] \[\frac{1}{v}-\frac{1}{-30}=\frac{1}{20}\] \[v=60cm\] Refraction from lens for \[{{I}_{3}}\] \[\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\] \[\frac{1}{v}-\frac{1}{+20}=\frac{1}{20}\] \[v=10cm\]