Question

a convex lens has focal lenght of 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens ? Find the magnification produced by the lens.

Answer 1

then the magnification is 40

Answer 2

Focal length(f)=15cm

Image distance(v)=10cm

Object distance(u)=?

1/f=1/v - 1/u

1/15=1/10- 1/u

1/u=1/10 - 1/15

1/u=3-2/30

1/u=1/30

u=30cm

So the object is placed at a distance of 30cm behind the lens.

Magnification(m)=v/u

=10/30

=1/3

=+0.33

Hope it helps you