Question

If a student desires to produce three times larger and an erect image from a double convex lens with focal length of 15 cm ,then he should place the object from the lens at ;

Answer 1

The object has to be placed between the lens and the focus.
di= distance between the image and the lens;
do=distance between the object and the lens;
F =focal length.
do/di=h/H=1/3 =>
3•do=di
1/F =1/do-1/di,
1/F= =
=2/3•do,
do=2F/3 =2•0.15/3=0.1 m.