A convex lens forms a real image of pencil at a distance of 50 cm from the lens . The image formed is of the same size as the object . Find the focal length and power of the lens. At what distance is the pencil placed from the lens ?

A convex lens forms a real image of pencil at a distance of 50 cm from

1.	A convex lens forms a real image of pencil at a distance of 50 cm from the lens . The image formed is of the same size as the object . Find the focal length and power of the lens. At what distance is the pencil placed from the lens ?
Answer» SOLUTION :DATA : Convex lens ,v=50 cm `M=-1 ,F= ?"h"_(1)=?, U=?` `M=-1=v/u` `therefore u=-v=-50cm"" `(object distance) The pencil is PLACED at 50 cm from the convex lens . `1/f=1/v-1/u=1/(50cm)-1/(-50cm) =(2)/(50 cm)` `therefore f=(50cm)/(2)=25 cm` `P=1/f=1/(25cm)=1/(0.25 m)=4 D` The power of the lens =4 D.