A point object is placed at a distance of 10 cm and its real image is formed at a distance of 20 cm from a concave mirror. If the object is moved by 0.1 cm towards the mirror, the image will shift by about

Mirror formula1f=1v+1u⇒1f=1-20+1-10⇒f=203 cm.If object moves towards the mirror by 0.1 cm then u = (10 - 0.1) = 9.9 cm. Hence again from mirror formula 1-20/3=1v'=1-9.9⇒v'=20.4 cm.i.e., image shifts away from the mirror by 0.4 cm.