Question

A student uses a converging lens to produce an enlarged, virtual image of a scale she wishes to read

accurately. The focal length of the lens is 10 cm . What is the suitable distance between the scale and

the lens, whether it will be more or less than 10cm?

Answer 1

GIVEN:

A converging lens (convex lens) of focal length $(f=10cm)$

we know,

nearest optimal distance between normal human eye and lens $D=25cm$

and according to Lens formula,

$\boxed{{1\over v}-{1\over u}={1\over f}}$

here,

u= object distance is to be find

v=(-25) virtual image distance of normal vision

f=10 focus

after putting values in above

we get,

$\boxed{f=7.1cm}$

as we know that to form virtual image object is kept between focus and pole ....i.e,

<10 cm