question_answer

A convex lens, of focal length 30cm, a concave lens of focal length 120 cm, and a plane mirror are arranged as shown. For an object kept at a distance of 60 cm from the convex lens, the final image, formed by the combination, is a real image, at a distance of : Focal length| |Focal length| = 30 cm =120 cm   JEE Main Online Paper (Held On 09 April 2016)

A) 70 cm from the concave lens                

B) 60 cm from the convex lens                

C) 60 cm from the concave lens                

D) 70 cm from the convex lens

Correct Answer: D

Solution :

Ans. [BONUS]                 \[{{f}_{1}}=+300cm\]      \[f=-120cm\] Event .1 Refraction from convex lens.                 F = + 30 \[\frac{1}{v}-\frac{1}{-60}=\frac{1}{30}\]               \[v=+60cm\] Event .2 Refraction from concave lens \[\frac{1}{v}-\frac{1}{+40}=\frac{1}{-120}\]          \[v=+60cm\] Event .3 Refraction from plane mirror Event .4 Refraction from concave lens \[\frac{1}{v}-\frac{1}{-40}=\frac{1}{-120}\]                           \[v=-30\] Event .5 Refraction from convex lens \[\frac{1}{v}-\frac{1}{-50}=\frac{1}{30};v=+75cm\]