Question

An object is placed on the axis of a convex lens. Its image is real and 3 times magnified. Calculate distance of object from lens if focal length of lens is 10 cm.

• A. 15 cm
• B. 20 cm
• C. $\frac { 40 } { 3 }$ cm
• D. 10 cm

Answer 1

Answer: (C)

$\frac { 40 } { 3 }$ cm

Answer 2

m = – 3 = $\frac { \mathrm { f } } { \mathrm { f } + \mathrm { u } }$

\ – 3 = $\frac { + 10 } { + 10 + u }$

\ – 30 – 3u = 40

\ u = $\frac { - 40 } { 3 }$ cm

nd apply transformations.