Question

A 4cm tall object is placed to the principal axis of a convex lens of focal length 20cm. the distance of the object from the length is 15cm. find the nature, position and size of the image.

Answer 1

Height of object ho = 4 cm Focal lenght of convex lens = 20 cm Object distance u = -15 cm Image distance v = ? Image height hi = ? Lens formula: 1/v  -  1/u  =  1/f                         1/v  = 1/f  +  1/u                                =  1/20  +  1/(-15)                                = -1/60 ⇒  v = - 60 cmThe image distance is 60 cm on the same side of the lens as the object.Magnification m = v/u = (-60)/(-15) = 4 = hi/ho = hi/4 ⇒   hi = 4 x 4 = 16 cm The image is enlarged and erect. So a virtual, erect, enlarged image is formed at 60 cm from the optic centre on the same side of the lens as the object is positioned