Question

A convex lens of focal length 10 cm is placed at a distance of 12 cm from a wall . How far from the lens should an object be placed so as to form its real image on the wall?

Answer 1

by mirror formula,

1/u - 1/y = 1/f
sign convention is distance from the centre of the lens to be positive in one direction and negative in the other -

=>> 1/12 - 1/u = 1/10
=>> 1/u - 1/12 - 1/10 = -1/60
=>> The object to be place on side opposite to that of the wall at a distance of 60 cm, from the lens.
I hope it's help U :-)

Answer 2

v=12cm,f=10cm 1/v+1/u = 1/f , u= f×v/v-f = 10×12/12-10= 120/2= 60cm