Q.
A point object is placed at distance of 20 cm from a thin planoconvex lens of focal length 15 cm. The plane surface of the lens is now silvered. The image created by the system is at
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
Explanation
(c) Refraction from lens
$\frac{1}{v₁} = \frac{1}{- 20} = \frac{1}{15}$
$\therefore\ \ \ \ v = 60\ cm + ve$ direction
Ie, 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$\mathbf{\ }\frac{1}{v_{3}} - \frac{1}{60} = \frac{1}{15}$ + ve direction
Or $v_{3} = 12\ cm$
Therefore, the final image is formed at 12 cm to the left of the lens system.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.