25.6 Image formation by lenses  (Page 10/19)

An object is 25 cm in front of a converging lens with a focal length of 25 cm. Where will the resulting image be located?

1. 25 cm in front of the lens
2. 25 cm behind the lens
3. 50 cm behind the lens
4. at infinity (either in front of or behind the lens)

A detective holds a magnifying glass 5.0 cm above an object he is studying, creating an upright image twice as large as the object. What is the focal length of the lens used for the magnifying glass?

A student wishes to predict the magnification of an image given the distance from the object to a converging lens with an unknown index of refraction. What data must the student collect in order to make such a prediction for any object distance?

1. A specific object distance and the image distance associated with that object distance.
2. A specific image distance and a determination of whether the image formed is upright or inverted.
3. The diameter and index of refraction of the lens.
4. The radius of curvature of each side of the lens.

Given a converging lens of unknown focal length and unknown index of refraction, explain what materials you would need and what procedure you would follow in order to experimentally determine the focal length of the lens.

It can be argued that a flat piece of glass, such as in a window, is like a lens with an infinite focal length. If so, where does it form an image? That is, how are $d_{\text{i}}$ and $d_{\text{o}}$ related?

You can often see a reflection when looking at a sheet of glass, particularly if it is darker on the other side. Explain why you can often see a double image in such circumstances.

When you focus a camera, you adjust the distance of the lens from the film. If the camera lens acts like a thin lens, why can it not be a fixed distance from the film for both near and distant objects?

A thin lens has two focal points, one on either side, at equal distances from its center, and should behave the same for light entering from either side. Look through your eyeglasses (or those of a friend) backward and forward and comment on whether they are thin lenses.