Question

a 4 cm tall object is placed perpendicular to principal axis below the principal axis of a convex lens what is the sign convention for object size

Answer 1

According to the sign convention..

Right and up is positive.

Left and down is negative.

Thus object size will be negative..

Answer 2

Answer:

Height of object ho = 4 cm

Focal lenght of convex lens = 24 cm

Object distance u = -16 cm

Image distance v = ?

Image height hi = ?

Lens formula: 1/v  -  1/u  =  1/f

                         1/v  = 1/f  +  1/u

                                =  1/24  +  1/(-16)

                                = -1/48

⇒  v = - 48 cm

The image distance is 48 cm on the same side of the lens as the object.

Magnification m = v/u = (-48)/(-16) = 3 = hi/ho = hi/3

⇒   hi = 3 x 3 = 9 cm