Question

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

Answer 1

Given :

focal length f = 30 cm

image distance v = 60 cm

convex lens

object distance U = ??

we know that,

1 / f = 1 / v - 1 / U

implies,

1 / U = 1 / v - 1 / f

1 / U = 1 / 60 - 1 / 30

1 / U = ( 1 - 2 ) / 60

1 / U = - 1 / 60

U = - 60

therefore the object distance is 60cm.

magnification of lens is

m = V / U

implies,

m = 60 / -60

m = -1 cm

therefore the magnification produced is equals to -1

for the following answer it can be clearly noticied that the object is placed at a distance of 2F and the image is formed at 2F.

_____________________________