26.5 Telescopes  (Page 3/5)

Which of the following is an advantage to using a concave mirror in the construction of a telescope?

1. The telescope can gather more light than a telescope using lenses.
2. The telescope does not suffer from chromatic aberration.
3. The telescope can provide greater magnification than a telescope using lenses.

1. I and III only
2. II only
3. I and II only
4. I, II, and III

A spherical mirror is used to construct a telescope.

1. Using the picture below, draw two rays incident on the object mirror and continue their path through the eye lens.

   

2. The plane mirror is replaced with a concave lens. Using the picture below, draw the path of two incident rays.

   

3. Using the concave lens setup, describe the final image created by the concave lens.

Two concave lenses, of focal lengths 500 mm and 20 mm, are used in the construction of a telescope. Given any potential arrangement, what is the largest possible magnification the telescope may have?

1. 100×
2. 10,000×
3. 25×
4. 4×

If you want your microscope or telescope to project a real image onto a screen, how would you change the placement of the eyepiece relative to the objective?

What is the angular magnification of a telescope that has a 100 cm focal length objective and a 2.50 cm focal length eyepiece?

Find the distance between the objective and eyepiece lenses in the telescope in the above problem needed to produce a final image very far from the observer, where vision is most relaxed. Note that a telescope is normally used to view very distant objects.

A large reflecting telescope has an objective mirror with a $\text{10}\text{.}\mathrm{0\; m}$ radius of curvature. What angular magnification does it produce when a $3\text{.}\text{00 m}$ focal length eyepiece is used?

A small telescope has a concave mirror with a 2.00 m radius of curvature for its objective. Its eyepiece is a 4.00 cm focal length lens. (a) What is the telescope’s angular magnification? (b) What angle is subtended by a 25,000 km diameter sunspot? (c) What is the angle of its telescopic image?

A $\mathrm{7.5\times }$ binocular produces an angular magnification of $-7\text{.}\text{50}$ , acting like a telescope. (Mirrors are used to make the image upright.) If the binoculars have objective lenses with a 75.0 cm focal length, what is the focal length of the eyepiece lenses?

Construct Your Own Problem

Consider a telescope of the type used by Galileo, having a convex objective and a concave eyepiece as illustrated in [link] (a). Construct a problem in which you calculate the location and size of the image produced. Among the things to be considered are the focal lengths of the lenses and their relative placements as well as the size and location of the object. Verify that the angular magnification is greater than one. That is, the angle subtended at the eye by the image is greater than the angle subtended by the object.