You have a lens. Suggest an experiment to find out the focal length of the lens.
Aim : To find focal length of given lens.
Apparatus : Object (candle), convex lens, V-stand, screen.
- Take a V-stand and place it on a long table at the middle.
- Place a convex lens on the V-stand.
- Imagine the principal axis.
- Light a candle and ask your friend to take the candle far away from the lens along the principal axis.
- 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.
- Measure the image from V-stand of lens.
- 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.