Aim : To find focal length of given lens.
Apparatus : Object (candle), convex lens, V-stand, screen.
1) Take a V-stand and place it on a long table at the middle.
2) Place a convex lens on the V-stand.
3) Imagine the principal axis.
4) Light a candle and ask your friend to take the candle far away from the lens along the principal axis.
5) Adjust a screen (prepared with paper placed perpendicular to the axis) which
is other side of the lens until we will get a point sized image.
6) Measure the image from V-stand of lens.
7) This gives the focal length of given lens because distant objects from image on focus so the distance between image and lens is nothing but focal length of given lens.