Question

an object of height 4.0 cm is placed at a distance of 30 cm from the optical centre 'O' of a convex lens of focal length 20 cm. draw a ray diagram to find position and size of the image formed. mark optic centre 'O' and principal focus 'F' on the diagram. also find the appropriate ratio of size of image to the size of the object

Answer 1

the size of image will be -8 cm and the ratio of size of the image to the size of the object will be2:1
v can be found out by the lens formula
the ray diagram will be the same when the object is placed between F and 2F and the image forms beyond 2F'.

Answer 2

Using the lens formula u cn find the image distance (v) 1/20-1/30 = 1/60 so v=60 by formula of magnification m, =v/u u gt m= 60/-30 = - 2 so dats the ratio..