Question

Where should an object be placed in front of a convex lens of focal length 0.12 m to obtain a real image of size three times the size of the object, on the screen ?

Answer 1

Focal length of a convex lens ,f=+0.12
m=-3 (real image)
For a lens ,magnification is
m=v/u
-3=v/u
v=-3u

Lens formulais,
1/f=1/v-1/u
1/-3u-1/u=1/0.12
-4/3u=1/0.12
3u=-0.48
u=-0.16