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Integrated Coordinated Science for the 21st Century

Active Physics
+ Chapter 6
Is Anyone Out There?
Answers
Physics To Go
  1. Two convex lenses, one with a relatively long focal length and one with a relatively short focal length.
  2. a) Yes.
    b) At the focus of the objective (also at the focus of the eyepiece); it would be near the eyepiece.
    c) The convex eyepiece (it’s a magnifier).
  3. a) The telescope becomes longer, too. The separation of the lenses is the sum of their focal lengths. Most of that distance is the focal length of the objective.
    b) First, the large image would be dim, because the same amount of light would be spread over a large image. To maintain the brightness of the image, you would have to increase the diameter of the objective. Second, if the telescope were made extremely long, it would be difficult to mount and to aim.
  4. The objective makes a real image inside the tube. The eyepiece magnifies this image.
  5. a) The diameter of the objective determines how much light enters the telescope.
    b) To let in as much light as possible.
  6. Divide the focal length of the objective by the focal length of the eyepiece.
  7. a) The device is a spyglass.
    b) It has a lens in either end, just like the telescopes you made.
    c) A lens with a long focal length at the end pointed toward the object and a lens with a short focal length at the end held to the eye.
  8. The advertisement can describe a simple refracting telescope.
  9. We can point our instruments at stars that have planets and try to observe signals sent by another civilization.