Question

  A convex  lens has focal length of  30 cm. at what distance should object be placed  from the lens so  that it  forms an image  at 60 cm on  other  side of  the lens?  Find the  magnification produced by  the  lens.

Answer 1

use Lens formula,
1/v - 1/u = 1/f
where,
v = image distance from lens
u = object distance from lens
f = focal length

here ,
f = 30 cm { for convex lens f is positive }
v = 60cm
now,
1/60 - 1/u = 1/30

1/60 - 1/30 = 1/u

-1/60 = 1/u

u = -60 cm

hence, object distance also 60cm but left side of convex lens . in which position of image is right side.

now,
magnification = ( image distance )/(object distance ) = 60/(-60) = -1

magnification = -1
it means height of image = height of object . but both lies just opposite sides of lens .

Answer 2

hope this will help you