Deck 4: Light and Telescopes

Question 1

Which of the following photons carry the least amount of energy?

A) a blue photon of the visible spectrum, whose wavelength is 450 nm
B) an infrared photon, whose wavelength is 10-5 meter
C) a red photon in the visible spectrum, whose wavelength is 700 nm
D) a microwave photon, whose wavelength is 10-2 meter

Answer 1

a microwave photon, whose wavelength is 10-2 meter

Question 2

How does the speed of light traveling through a medium (such as air or glass)compare to the speed of light in a vacuum?

A) It is the same as the speed of light in a vacuum.
B) It is always less than the speed of light in a vacuum.
C) It is always greater than the speed of light in a vacuum.
D) Sometimes it is greater than the speed of light in a vacuum, and sometimes it is less, depending on the medium.

Answer 2

It is always less than the speed of light in a vacuum.

Question 3

A red photon has a wavelength of 650 nm.An ultraviolet photon has a wavelength of 250 nm.The energy of an ultraviolet photon is ________ than a red photon.

A) 2.6 times larger
B) 6.8 times larger
C) 2.6 times smaller
D) 6.8 times smaller

Answer 3

2.6 times larger

Question 4

If the wavelength of a beam of light were to double,how would that affect its frequency?

A) The frequency would be four times larger.
B) The frequency would be two times larger.
C) The frequency would be two times smaller.
D) The frequency would be four times smaller.
E) There is no relationship between wavelength and frequency.

Question 5

The part of the human eye that acts as the detector is the:

A) retina.
B) pupil.
C) rods.
D) cones.

Question 6

Using the figure below,which type of electromagnetic wave has a wavelength of approximately 10-⁵ meter?

A) X-rays
B) infrared
C) microwave
D) radio

Question 7

The speed of light in a vacuum is:

A) 300,000 m/s.
B) 300,000 mph.
C) 300,000 km/s.
D) 300,000,000 mph.
E) infinite.

Question 8

What are two properties shared between the eye and all other astronomical detectors?

A) integration time and wavelength sensitivity
B) quantum efficiency and integration time
C) wavelength sensitivity and signal strength
D) quantum efficiency and signal strength

Question 9

As wavelength increases,the energy of a photon ________ and its frequency ________.

A) increases; decreases
B) increases; increases
C) decreases; decreases
D) decreases; increases

Question 10

Which formula denotes how the speed of light is related to its wavelength and frequency?

A) c = lf
B) c = l/f
C) c = f/l
D) c = 1/lf

Question 11

Before CCDs were invented,what was the device most commonly used for imaging with optical telescopes?

A) Polaroid cameras
B) photographic glass plates
C) high-speed film
D) video cameras

Question 12

Light with a wavelength of 600 nm has a frequency of:

A) 5.0 × 106 Hz.
B) 5.0 × 1014 Hz.
C) 5.0 × 1011 Hz.
D) 2.0 × 1015 Hz.

Question 13

The speed of light was first determined by which scientist?

A) Galileo
B) Rømer
C) Kepler
D) Newton
E) Einstein

Question 14

The fact that the speed of light is constant (as it travels through a vacuum)means that:

A) photons with longer wavelengths have lower frequencies.
B) radio wave photons have shorter wavelengths than gamma-ray photons.
C) X-rays can be transmitted through the atmosphere around the world.
D) All of the above are true.

Question 15

Which of the following lists different types of electromagnetic radiation in order of increasing wavelength?

A) radio waves, infrared, visible, ultraviolet, X-rays
B) gamma rays, ultraviolet, visible, infrared, radio waves
C) gamma rays, X-rays, infrared, visible, ultraviolet
D) X-rays, infrared, visible, ultraviolet, radio waves
E) radio waves, ultraviolet, visible, infrared, gamma rays

Question 16

The light-year is a unit of:

A) time.
B) distance.
C) speed.
D) energy.

Question 17

Using the figure below,which type of electromagnetic wave has a frequency of approximately 3 × 10¹⁷ Hz?

A) X-rays
B) infrared
C) microwave
D) radio

Question 18

The Voyager 1 spacecraft is currently 16.5 billion km from Earth and heading out of our Solar System.How long does it take radio messages from Voyager 1 to reach us?

A) 1.5 days
B) 15 hours
C) 1.5 weeks
D) 15 minutes

Question 19

How do the wavelength and frequency of red light compare to the wavelength and frequency of blue light?

A) Red light has a longer wavelength and higher frequency than does blue light.
B) Red light has a longer wavelength and lower frequency than does blue light.
C) Red light has a shorter wavelength and higher frequency than does blue light.
D) Red light has a shorter wavelength and lower frequency than does blue light.

Question 20

Which properties of light changes in a refractive medium?

A) wavelength
B) frequency, speed, and wavelength
C) wavelength and speed
D) speed

Question 21

The angular resolution of a ground-based telescope is usually set by:

A) diffraction.
B) refraction.
C) the focal length.
D) atmospheric seeing.

Question 22

The major advantage CCDs have over other imaging techniques is that:

A) they have a higher quantum efficiency.
B) they have a linear response to light.
C) they yield output in digital format.
D) they operate at visible and near-infrared wavelengths.
E) All of the above are true.

Question 23

The angular resolution of the largest single-dish radio telescope in the United States,the 100 m Green Bank Telescope,is closest to________ when it operates at a wavelength of 20 cm.

A) 0.6°
B) 0.6 arcmin
C) 0.6 arcsec
D) 6 arcsec

Question 24

The most important improvement that photography provides over naked-eye observations is:

A) it is possible to observe a larger field of view with photographic plates.
B) the quantum efficiency is higher for photographic plates.
C) the image resolution is much better for photographic plates.
D) it is possible to detect fainter objects with the use of photographic plates.

Question 25

Arrays of radio telescopes can produce much better resolution than single-dish telescopes because they work based on the principle of:

A) reflection.
B) refraction.
C) diffraction.
D) interference.

Question 26

The light-gathering power of a 4-meter telescope is ________ than that of a 2-meter telescope.

A) 8 times larger
B) 4 times larger
C) 16 times smaller
D) 2 times smaller

Question 27

The 305-meter Arecibo radio telescope in Puerto Rico has a resolution that is closest to that of:

A) the Hubble Space Telescope (0.1 arcsec).
B) a human eye (1 arcmin).
C) the Chandra X-ray Telescope (0.5 arcsec).
D) a 1-meter optical telescope (1 arcsec).

Question 28

As a beam of light travels from one medium to another,the change in direction of the beam of light depends on:

A) the wavelength of the light.
B) the index of refraction of the medium through which it is traveling.
C) the index of refraction of the medium into which it is moving.
D) all of the above

Question 29

Ultraviolet radiation is hard to observe primarily because:

A) Earth's atmosphere easily absorbs it.
B) no space-based telescopes operate at ultraviolet wavelengths.
C) only the lowest-mass stars emit ultraviolet light.
D) very few objects emit at ultraviolet wavelengths.

Question 30

Both reflecting and refracting telescopes suffer from:

A) chromatic aberration.
B) diffraction effects and chromatic aberration.
C) greater increase in weight for a given increase in aperture.
D) diffraction effects.

Question 31

Which of the following causes the biggest problem in detecting infrared photons from an astronomical object?

A) smog
B) carbon dioxide
C) water vapor
D) light pollution

Question 32

Which of the following properties is (are)improved by placing telescopes in space?

A) quantum efficiency
B) integration time and angular resolution
C) quantum efficiency and integration time
D) ability to observe at multiple wavelength regions and angular resolution

Question 33

A prism is able to spread white light out into a spectrum of colors based on the property of:

A) reflection.
B) refraction.
C) scattering.
D) interference.

Question 34

When we determine the angular resolution of an interferometric array of radio telescopes using the formula q µ l/D,the variable D stands for the:

A) diameter of the telescopes.
B) separation between the telescopes.
C) number of telescopes.
D) focal length of the telescopes.

Question 35

The speed of a light wave:

A) is altered by a refractive medium.
B) is reduced whenever reflection occurs.
C) is not altered by reflection or refraction.
D) is not altered by refraction.

Question 36

The diffraction limit of a 4-meter telescope is ________ than that of a 2-meter telescope.

A) two times larger
B) four times larger
C) two times smaller
D) four times smaller

Question 37

Cameras that use adaptive optics provide higher spatial resolution images primarily because:

A) they operate above Earth's atmosphere.
B) they capture infrared light, which has a longer wavelength than visible light.
C) deformable mirrors are used to correct the blurring due to Earth's atmosphere.
D) composite lenses correct for chromatic aberration.

Question 38

How does the resolution of a telescope depend on its focal length?

A) The longer the focal length is the better the resolution is.
B) The longer the focal length is the worse the resolution is.
C) There is no relation between resolution and focal length.

Question 39

Why do reflecting telescopes usually have a secondary mirror in addition to a primary mirror?

A) to increase the light-gathering power
B) to make the telescope shorter
C) to increase the focal length
D) to combat chromatic aberration

Question 40

One reason to prefer a reflecting over a refracting telescope is its:

A) lack of chromatic aberration.
B) shorter length for the same aperture size.
C) lighter weight for larger apertures.
D) All of the above are valid reasons.

Question 41

Does the wavelength of a wave change when entering a refractive medium? Explain.

Question 42

Discuss two tools that modern astronomers use to explore the cosmos that are different from traditional optical telescopes,and give an example of how and why each is used.

Question 43

Explain two major advantages of CCDs over other imaging techniques.

Question 44

The SETI project's Allen Telescope Array will have 350 radio dishes,each with an individual diameter of 6 meters,spread out over a circle whose diameter is 1 km.What would this array's spatial resolution be when it operates at 5 cm?

A) 10 arcsec
B) 0.10 arcsec
C) 10 arcmin
D) 1.0 arcmin

Question 45

Explain how adaptive optics help compensate for atmospheric seeing.

Question 46

Explain why the largest telescopes are not refracting telescopes.

Question 47

Give an explanation as to why electromagnetic radiation does not require a medium for propagation.

Question 48

The image below shows the Very Large Array in New Mexico.What is the benefit of using multiple telescopes in such an array?

Question 49

Explain why stars twinkle when viewed from the ground.Would they twinkle if viewed from outer space?

Question 50

What type of telescope is shown in the image below?

Question 51

How do telescopes advance astronomical science?

Question 52

Why is the wavelength of a reflected light wave generally equal to that of the incident wave?

Question 53

A spaceship approaches Earth at 0.9 times the speed of light and shines a powerful searchlight onto Earth.How fast will the photons from this searchlight be moving when they hit Earth?

Question 54

Using the figure below,list the different types of electromagnetic waves in order of increasing wavelength.

Question 55

What is the diffraction limit of a 4-meter telescope observing at a wavelength of 650 nm?

Question 56

Compare and contrast the wavelengths,frequencies,speeds,and energies of red and blue photons.

Question 57

Which telescope would collect 100 times more light than a 1-meter telescope?

A) 100-meter telescope
B) 50-meter telescope
C) 30-meter telescope
D) 10-meter telescope

Question 58

The two Keck 10-meter telescopes,separated by a distance of 85 meters,can operate as an interferometer.What is its resolution when it observes in the infrared at a wavelength of 2 μm?

A) 0.01 arcsec
B) 0.005 arcsec
C) 0.05 arcsec
D) 0.2 arcsec

Question 59

Where should telescopes purposed to observe the high energy light from the death of stars be located?

Question 60

Using the figure below,list the different types of electromagnetic waves in order of increasing frequency.

Question 61

What is the angular resolution of a 1-meter,ground-based,optical telescope that observes at a wavelength of 600 nm compared to that of a 300-ft,single-dish radio telescope that observes at a wavelength of 21 cm?

Question 62

Compare the light-gathering power of the human eye to that of a 10-inch telescope.