HW 5

Why do radio telescopes have such poor resolution?

because radio waves have such a long wavelength

Based on what you learned about light, select all of the correct statements from the following list.

Light can act both as a wave and a particle. High frequency photons carry more energy than long wavelength photons. All electromagnetic waves travel at the speed of light. A photon is a particle of light.

Based on what you learned about astronomy from space, select all of the correct statements from the following list.

Most types of electromagnetic waves are not visible to ground-based telescopes. The Compton, Chandra and Spitzer telescopes are all examples of space telescopes.

If you were to make a telescope using the two lenses shown here, which lens should you use for the primary (objective) and which for the eyepiece?

One uses top lens for the primary and bottom lens for the eyepiece.

Based on what you learned about radio telescopes, select all of the correct statements from the following list.

Radio telescopes have to be larger than optical telescopes, since radio waves are longer than visible light waves. Radio waves can travel through obstacles that block out waves of visible light. Radio telescopes are used to detect cool hydrogen.

Based on what you learned about telescopes, select all of the correct statements from the following list.

Recently built modern telescopes are reflectors.

Why are short tubes an advantage for large telescopes?

Short tubes can fit inside a smaller observatory building. Short tubes can be supported with less vibration. Short tubes weigh less than those of refracting telescopes

Which of the following is a reason that reflecting telescopes have shorter tubes than refracting telescopes?

The light goes up the tube and then back down.

Refracting telescopes are so called for which of the following reasons?

The light is bent to a focus.

What is the biggest advantage of a reflecting telescope?

The light never passes through glass.

Of the two telescopes shown here, which will allow you to see dimmer objects?

The telescope on the left.

Which of the following is true of reflecting telescopes?

They focus light by bouncing it off of optical surfaces.

Most of Galileo's telescopes were only about 2 cm in diameter. Should he have been able to resolve two stars 6.0 seconds of arc apart?

Yes, the object is sufficiently large

Why have no large refracting telescopes been built since 1900?

all of the below

You see a telescope advertised as 200 power. (a) What quality of a telescope is probably being advertised? (b) Would you want to buy the telescope based on this advertisement? (c) What quality of a telescope is least important? (d) What qualities of a telescope are important to you as a potential buyer? (e) Which would not be a way to make the advertisement better?

magnifying power Maybe, depending on other factors, like the diameter of the objective or the quality of the optics. all of the above are important Make sure it specifies that the 200 is magnifying power.

In this figure you can see that different wavelengths of light are refracted (bent) by different amounts. Which wavelengths are bent by the greatest amount?

short wavelengths

In a telescope, which of the following is the optical element with the shortest focal length?

the eyepiece

Which of the following is the first thing light hits when it enters a telescope?

the primary lens or mirror

What is the purpose of the colors in a false-color image?

to indicates areas of different intensity in an image

The visible part of the electromagnetic spectrum can be divided into seven color bands: red, orange, yellow, green, blue, indigo, and violet (from long to short wavelength). A single photon of which of these colors has the greatest amount of energy?

violet

The entire electromagnetic spectrum can be divided into seven bands: radio, microwave, infrared, visible, ultraviolet, X ray, and gamma ray (from longest to shortest wavelength). To which of these two bands is Earth's atmosphere the most transparent?

visible and radio

Based on what you learned about these instruments, select all of the correct statements from the following list.

-Photography in astronomy has mostly been replaced by CCD imaging. -Prisms and gratings spread light out into its spectrum by bending the direction of different wavelengths of light in different directions. -In modern spectrographs, gratings have replaced prisms. -Spectral lines observed from astronomical objects tell astronomers what atoms are present.

If you build a telescope with a focal length of 2.4 m, what focal length should the eyepiece have to give a magnification of 100 times?

0.024 m

The thickness of the plastic in plastic bags is about 0.001 mm. How many wavelengths of orange light is this? (Assume a wavelength of 590 nm for orange light.)

1.69

How does the light-gathering power of a 2 m telescope compare with that of the human eye? (Hint: Assume that the pupil of your eye can open to about 0.8 cm.)

62500

(a) Rank the following colors of visible light in order of increasing wavelength: blue, green, red, yellow. (b) Rank the following colors of visible light in order of increasing frequency: green, red, violet, yellow. (c) Rank the following types of electromagnetic radiation in order of decreasing wavelength: infrared, gamma-ray, radio, ultraviolet, visible.

A. least blue green yellow greatest red B. least red yellow green greatest violet C. greatest radio infrared visible ultraviolet least gamma-ray