A lens has a focal length of -10 cm.  If the image of an object is located at -20 cm, what is the distance of the object?

8. Given a biconvex lens made of glass of index 1.5. The magnitude of the radius of curvature is the same for both surfaces. The lens has a focal length of 75 mm. What focal length would the lens have if it had the same surface curvatures but an index of 3.0? Express in millimeters.

1. 2. 3. What is the focal length of -4.50 D lens? Where is the focal point in the above lens and is it in front of or behind the lens? Would the image in the above lens be real or virtual?

6. A convex lens of focal length 25 cm is at a distance of 60 cm from a concave mirror of focal length 20 cm (see figure below). A lightbulb is 80 cm from the lens. (a) Where does the lens form an image of the lightbulb? (b) Where does the mirror form an image of the first image? (c) Where does the lens form the (final) image of the second image?

6. An object is placed 8.5 cm in front of a convex (converging) spherical lens. Its image forms 3.9 cm in front of the lens. What is the focal length of the lens? *   D) 19 cm       C) 9.6 cm       B) 2.7 cm       A) 6.1 cm

16.

8. On one side of a converging lens of focal length 59.1 cm, you position an object of height 3.02 cm somewhere along the principal axis. The resultant image has a height of 15.10 cm. How far from the lens is the object located?     70.9 cm     28.4 cm     92.2 cm     42.5 cm

If the eyepiece of a telescope is replaced with an eyepiece with a focal length half as long, the magnifying power is   a. four times greater.   b. two times greater.   c. four times less.   d. two times less.   e. the same as with the original eyepiece.