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Optics and Telescopes Practice Problems

By — McGraw-Hill Professional
Updated on Sep 18, 2011

Review the following concepts if needed:

 

Optics and Telescopes Practice Problems

A good score is 8 correct. Answers are given at the end.

1. A simple convex lens has a focal length that varies slightly depending on the wavelength of the light passing through it. When such a lens is used as the objective of a telescope, this effect results in

(a) dispersion.

(b) spherical aberration.

(c) chromatic aberration.

(d) nothing! The premise is wrong. A convex lens has the same focal length for all wavelengths of light passing through it.

 

2. At the surface of Earth, the maximum useful magnification of a telescope, no matter how large the objective, is approximately 500× because of

(a) skyglow.

(b) air turbulence.

(c) dispersion.

(d) diffraction.

 

3. A spectrometer can record its image on

(a) photographic film.

(b) an eyepiece.

(c) a secondary mirror.

(d) a gegenschein device.

 

4. The use of a CCD with a telescope can enhance the

(a) focal length.

(b) magnification.

(c) image contrast.

(d) spectral output.

 

5. According to the law of reflection,

(a) a ray of light traveling from a medium having a low refractive index to a medium having a higher refractive index is reflected at the boundary.

(b) a ray of light traveling from a medium having a high refractive index to a medium having a lower refractive index is reflected at the boundary.

(c) a ray of light always reflects from a shiny surface in a direction exactly opposite the direction from which it arrives.

(d) None of the above

 

6. A Cassegrain type reflecting telescope has an objective mirror with a diameter of 300 mm and an eyepiece with a focal length of 30 mm. The magnification is

(a) 100×.

(b) 10×.

(c) 9,000×.

(d) impossible to calculate from this information.

 

7. A diverging lens

(a) can collimate converging rays of light.

(b) can focus the Sun’s rays to a brilliant point.

(c) is also known as a convex lens.

(d) is ideal for use as the objective in a refracting telescope.

 

8. Suppose that the speed of red visible light in a transparent medium is 270,000 km/s. What, approximately, is the index of refraction for this substance with respect to red light?

(a) 0.900

(b) 1.11

(c) 0.810

(d) It cannot be calculated from this information.

 

9. As the magnification of a telescope is increased,

(a) the image resolution decreases in direct proportion.

(b) physical stability becomes more and more important.

(c) the light-gathering area increases in direct proportion.

(d) dimmer and dimmer objects can be seen.

 

10. An advantage of space telescopes over Earthbound telescopes is the fact that

(a) space telescopes have less mass.

(b) space telescopes do not need power supplies.

(c) space telescopes are not subject to temperature changes.

(d) space telescopes are not subject to airglow.

 

Answers

1. C

2. B

3. A

4. C

5. D

6. D

7. A

8. B

9. B

10. D

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