Question

an object is placed 50 cm in front of screen. why should a convex lens of focal length 10 cm be placed in between them so as to form an image of the object on the screen.plzz solve it with diagram.

Answer 1

The given problem is illustrated in figure. When we fix the location of object and image formed screen, the object to lens ditance u and the image to lens distance v are interchanged to form imgaes by placing the lens at two locations. In the first case object is at a location beyond 2F where F is focal point so that diminshed image is formed. In second case object is between F and 2F and we get enlarged image.

From figure we can see u+v = 100; u-v=20;
solving for u and v we get u=60 cm and v = 40 cm.

focal length f is given by


focal length f = 24 cm