Question

A point object is placed at distance of 20 cm from a thin plano convex lens of focal length 15 cm. The plane surface of 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 totheleft of thesystem
• D. 12 cm totheright of thesystem

Answer 1

Answer: (C)

12 cm totheleft of thesystem

Answer 2

$\frac { 1 } { \mathrm { f } } = \frac { 2 } { \mathrm {~F} _ { \ell } } + \frac { 1 } { \mathrm {~F} _ { \mathrm { M } } } = \frac { 2 } { 15 } + \frac { 1 } { \infty } \Rightarrow \mathrm { f } = \frac { 15 } { 2 }$,

as concave mirror

$\frac { 1 } { v } = \frac { 1 } { f } - \frac { 1 } { u } = \frac { 1 } { - 15 / 2 } - \frac { 1 } { - 20 } = - \frac { 2 } { 15 } + \frac { 1 } { 20 }$ Ž $\mathrm { v } = 12 \mathrm {~cm}$ left side