Procedure 1: Forming Real Images with a Converging Lens

Question

a) Obtain the focal length
f of the small converging lens by focusing the image of a distant light bulb on the cardboard screen. Mount the lens and the screen on the meter stick. Position the screen at a convenient location, then adjust the lens location until a small, clear image forms on the screen. Take as the focal length the distance between the screen and the center of the lens using the positions of both (determined with the “pointers” where the supports clamp onto themeter stick). Make a sketch showing how the parallel rays go through the lens in this case.

Explain why the focal length of a diverging lens can't be measured by the method of Procedure 1.a).