A convex lens has a focal length of 10 cm. At what distance from the lens should the object be placed so that it forms a real and inverted image 20 cm away from the lens? What would be the size of the image formed if the object is 2 cm high? With the help of a ray diagram show the formation of the image by the lens in this case.
According to the question;
Object distance = u;
Image distance (v) = 20cm;
Focal length = 10cm
By lens formula;
⇒ u = -20cm.
Therefore, object is placed at 20 cm in front of lens.
Now;
Height of object h1= 2cm;
Magnification = =
Putting values of v and u
Magnification =
⇒
⇒
Height of image is 2 cm.
Negative sign means image is inverted.
Thus, the image is real, inverted and same as size of object.
Diagram below shows the image formation.