Question

A magnifying glass uses a converging lens with a focal length of 15.5 cm. It produces a virtual and upright image that is 2.9 times larger than the object.

A) How far is the object from the lens?

B) What is the image distance?

Answer 1

Focal length f = 15.5 cm

Magnification m = 2.9

                v / u = 2.9

from this image distance v = 2.9 u

Where u = obejct distance

(A). From the relation ( 1/ v ) -( 1/ u) = ( 1/ f )

                            ( 1/ -2.9 u) -( 1/-u) = ( 1/ 15.5) Since u and v are in virtual space region.So,we take uand v as -ve

                           ( 1/-2.9 u ) + ( 1/ u) = ( 1/ 15.5)

                           (-1 +2.9) / 2.9 u = ( 1/ 15.5)

                                    1.9 / 2.9 u = ( 1/ 15.5)

                                    2.9 u / 1.9 = 15.5

                                                 u = 10.15 cm

(B). Image distance v = 2.9 u

                               = 29.45 cm