In front of a concave lens of focal length 20 cm, a 6 cm tall object is placed so as to obtain its image at 15 cm from the lens. Distance of object from a concave lens will be -[[1]]cm.

In front of a concave lens of focal length

20 cm

, a

6 cm

tall object is placed so as to obtain its image at

15 cm

from the lens. Distance of object from a concave lens will be

- 60 cm .

Given,
Focal length,

f

- 20 cm

Image distance,

v = - 15 cm

From lens formula,

\frac{1}{v} - \frac{1}{u} = \frac{1}{f}

,where

f

is the focal length,

u

is the object distance and

v

is the image distance.

\frac{1}{- 15} - \frac{1}{u} = \frac{1}{- 20}

u = - 60 cm

In front of a concave lens of focal length $20 cm,$ a $6 cm$ tall object is placed so as to obtain its image at $15 cm$ from the lens. Distance of object from a concave lens will be $-$ [[1]] $cm$ .