Question

Focal length of the plano-convex lens is 15cm. A small object is placed at A as shown in figure. The plane surface is silvered. The image will form at

A. 60cm to the left of lens
B. 12cm to the left of lens
C. 60cm to the right of lens
D. 30cm to the left of lens

Answer 1

Correct Answer - b.
Refraction from lens: `(1)/(v_(1))-(1)/(-20)=(1)/(15)`
`v=60cm underset(+"ve direction") rarr`
i.e., first image is formed at 60cm to the rigth of lens system.
Reflection frm mirror:
After reflection from the mirro, the second image will be formed at a distance 60cm to the left of lens sytem.
Refraction from lens:
`(1)/(v_(3))-(1)/(60)=(1)/(15)larr+"ve direction"`
or `v_(3)=12cm`
Therefore, the final image is formed at 12 cm to the left of the lens system.