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

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