Procedure 1: Forming Real Images with a Converging Lens
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).
The method described in Procedure 1.a) is specifically designed to measure the focal length of a converging lens. This is because converging lenses are designed to bring parallel rays of light to a focal point, which forms a real and inverted image. By adjusting the position of the converging lens and the screen, we can find the exact distance at which the image appears clear and focused, and this distance is considered the focal length of the converging lens.
However, the same method cannot be used to measure the focal length of a diverging lens. This is because diverging lenses are designed to spread out parallel rays of light, causing them to diverge away from each other. As a result, a diverging lens does not form a real and focused image. Instead, the image formed by a diverging lens is virtual, upright, and can only be seen by looking through the lens.
Since a diverging lens does not form a real image, there is no fixed distance at which the image would appear clear and focused. Therefore, the method used in Procedure 1.a) cannot be applied to measure the focal length of a diverging lens. Different methods, such as measuring the apparent shift of a distant object when viewed through the lens, or using lens formula calculations, need to be used to determine the focal length of a diverging lens.