Optics Ques 63
- A point object is placed at a distance of $20$ $ cm$ from a thin plano-convex lens of focal length $15$ $ cm$. The plane surface of the lens is now silvered. The image created by the system is at
(2006, 3M)
(a) $60$ $ cm$ to the left of the system
(b) $60 $ $cm$ to the right of the system
(c) $12 $ $cm$ to the left of the system
(d) $12 $ $cm$ to the right of the system
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Answer:
Correct Answer: 63.(c)
Solution:
- Refraction from lens : $\frac{1}{v _1}-\frac{1}{-20}=\frac{1}{15}$
$\therefore \quad v=60 $ $cm \quad \rightarrow \quad +$ ve direction
i.e. first image is formed at $60 $ $cm$ to the right of lens system.
Reflection from mirror
After reflection from the mirror, the second image will be formed at a distance of $60$ $ cm$ to the left of lens system.
Refraction from lens
o
$ \frac{1}{v _3}-\frac{1}{60}=\frac{1}{15} \quad \leftarrow \quad+\text { ve direction } $
$v_3=12$ $ cm$
Therefore, the final image is formed at $12 $ $cm$ to the left of the lens system.
BETA
