The object distance is 17.2 cm
As we know, the lens formula is [tex] \frac{1}{f} [/tex] = [tex] \frac{1}{v} [/tex] + [tex] \frac{1}{u} [/tex]
where v = image distance from the lens
u = object distance from the lens
f = focal length of the lens
Alos, focal length of convex lens is positive.
⇒ [tex] \frac{1}{12} [/tex] = [tex] \frac{1}{40} [/tex] +[tex] \frac{1}{u} [/tex]
⇒ [tex] \frac{1}{u} [/tex] = [tex] \frac{1}{12} [/tex] - [tex] \frac{1}{40} [/tex]
⇒ [tex] \frac{1}{u} [/tex] = [tex] \frac{10-3}{120} [/tex]
⇒[tex] \frac{1}{u} [/tex] = [tex] \frac{7}{120} [/tex]
⇒ u = [tex] \frac{120}{7} [/tex] = 17.2 cm
