An object of height 3 cm is placed at 10 cm from a concave lens of focal length 15 cm. find the size of the image.

Explanation

Object distance u=-10 cm
[Object is placed on the left side]
Focal length f=-15 cm [`because` concave lens]
To find : Image distance v= ?
Height of the object h=3 cm.
`1/f =1/v -1/u`
`1/v = 1/f + 1/u`
`=1/(-15) + 1/(-10)`
`(-10-15)/(150)=(-25)/(150)`
`v=(150)/(25)=-6 cm`
Magnification m=`("Distance of the image")/("Distance of the object")`
`m=v/u`
`m =6/(10)=0.6`
`m=("height of the image")/("height of the object")`
`(h^1)/(h)`
`therefore h^1 =mxxh =0.6 xx 3`
`therefore ` Size of the image , `h^1` =1.8 cm