Deck 5: Light: the Cosmic Messenger

Question 1

How are wavelength, frequency, and energy related for photons of light?

A) Longer wavelength means lower frequency and lower energy.
B) Longer wavelength means higher frequency and lower energy.
C) Longer wavelength means higher frequency and higher energy.
D) Longer wavelength means lower frequency and higher energy.
E) There is no simple relationship because different photons travel at different speeds.

Answer 1

A

Question 2

Consider an atom of gold in which the nucleus contains 79 protons and 118 neutrons. What is its atomic number and atomic mass number?

A) The atomic number is 79, and the atomic mass number is 197.
B) The atomic number is 79, and the atomic mass number is 118.
C) The atomic number is 118, and the atomic mass number is 197.
D) The atomic number is 118, and the atomic mass number is 79.

Answer 2

A

Question 3

If you heat a gas so that collisions are continually bumping electrons to higher energy levels, when the electrons fall back to lower energy levels the gas produces

A) thermal radiation.
B) an absorption line spectrum.
C) an emission line spectrum.
D) X-rays.
E) radio waves.

Answer 3

C

Question 4

If a material is transparent, then it

A) reflects light well.
B) absorbs light well.
C) transmits light well.
D) scatters light well.
E) emits light well.

Question 5

Which of the following statements about electrons is not true?

A) Electrons orbit the nucleus rather like planets orbiting the Sun.
B) Within an atom, an electron can have only particular energies.
C) Electrons can jump between energy levels in an atom only if they receive or give up an amount of energy equal to the difference in energy between the energy levels.
D) An electron has a negative electrical charge.
E) Electrons have very little mass compared to protons or neutrons.

Question 6

When an atom loses an electron, it becomes

A) sublimated.
B) dissociated.
C) ionized.
D) an isotope.
E) a plasma.

Question 7

From lowest energy to highest energy, which of the following correctly orders the different categories of electromagnetic radiation?

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

Question 8

Without telescopes or other aid, we can look up and see the Moon in the night sky because it

A) emits visible light.
B) emits thermal radiation.
C) reflects infrared light.
D) reflects visible light.
E) glows through radioactive decay.

Question 9

Compared to the size of its nucleus, the size of an atom is about

A) the same.
B) ten times greater.
C) a hundred times greater.
D) a thousand times greater.
E) one hundred thousand times greater.

Question 10

How many atoms fit across the period at the end of this sentence?

A) hundreds
B) thousands
C) millions
D) billions
E) more than you could count in a lifetime

Question 11

How can an electron in an atom lose energy to go from a higher energy level to a lower energy level?

A) It loses kinetic energy.
B) It releases a photon equal in energy to its own energy drop.
C) It absorbs a photon equal in energy to its own energy drop.
D) It loses gravitational potential energy.
E) It exchanges gravitational potential energy for kinetic energy.

Question 12

Everything looks red through a red filter because

A) the filter emits red light and absorbs other colors.
B) the filter absorbs red light and emits other colors.
C) the filter transmits red light and absorbs other colors.
D) the filter reflects red light and transmits other colors.

Question 13

Which of the following statements about electrical charge is true?

A) Two negative charges will attract each other.
B) Two positive charges will attract each other.
C) A positive charge and a negative charge will repel each other.
D) A positive charge and a negative charge will attract each other.

Question 14

The wavelength of a wave is

A) how strong the wave is.
B) the distance between a peak of the wave and the next trough.
C) the distance between two adjacent peaks of the wave.
D) the distance between where the wave is emitted and where it is absorbed.
E) equal to the speed of the wave times the wave's frequency.

Question 15

We can see each other in the classroom right now because we

A) emit thermal radiation.
B) emit visible light.
C) emit infrared light.
D) reflect visible light.
E) reflect infrared light.

Question 16

The frequency of a wave is

A) the number of peaks passing by any point each second.
B) measured in cycles per second.
C) measured in hertz (Hz).
D) equal to the speed of the wave divided by the wavelength of the wave.
E) all of the above

Question 17

Which of the following statements about X-rays and radio waves is not true?

A) Neither X-rays nor radio waves can penetrate Earth's atmosphere.
B) X-rays have shorter wavelengths than radio waves.
C) X-rays and radio waves are both forms of light, or electromagnetic radiation.
D) X-rays have higher frequency than radio waves.
E) X-rays have higher energy than radio waves.

Question 18

An atom of the element iron has an atomic number of 26 and an atomic mass number of 56. If it is neutral, how many protons, neutrons, and electrons does it have?

A) 26 protons, 30 neutrons, 26 electrons
B) 26 protons, 30 neutrons, 30 electrons
C) 26 protons, 56 neutrons, 26 electrons
D) 13 protons, 43 neutrons, 13 electrons
E) 13 protons, 56 neutrons, 13 electrons

Question 19

An electron-volt is

A) the charge of one electron.
B) the energy of one electron.
C) the energy jump between the first and second energy levels of hydrogen.
D) an amount of energy much smaller than a joule.
E) an amount of energy much larger than a joule.

Question 20

Which of the following is not a way light and matter interact?

A) emission
B) absorption
C) evaporation
D) transmission
E) scattering

Question 21

Why do astronomers need different telescope designs to observe across the electromagnetic spectrum?

A) New telescopes incorporate new technology to increase their efficiency.
B) Telescopes have to adapt to the greater distortion of the atmosphere at shorter wavelengths.
C) Photons of different energy behave differently and require different collection strategies.
D) because light pollution is worse at radio wavelengths than visible wavelengths
E) Astronomers and engineers enjoy the challenge of making new telescope designs.

Question 22

There are more atoms in a glass of water than stars in the observable universe.

Question 23

A gas heated to millions of degrees would emit

A) mostly radio waves.
B) mostly X-rays.
C) mostly ultraviolet light.
D) an equal amount of all wavelengths of light.
E) no light, because it is too hot.

Question 24

If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we conclude about the planet?

A) The planet is actually two bodies, one moving toward us, the other away from us.
B) The planet is in the process of falling apart.
C) The planet is in the process of formation.
D) The planet is rotating.

Question 25

Which of the following statements about thermal radiation is always true?

A) A hot object emits photons with a longer wavelength than a cool object.
B) A hot object emits photons with a higher average energy than a cool object.
C) A hot object emits more radio waves than a cool object.
D) A hot object emits more X-rays than a cool object.

Question 26

What is an artificial star?

A) a point of light in Earth's atmosphere created by a laser for the purpose of monitoring atmospheric fluctuations
B) a satellite orbiting Earth
C) a meteor
D) a possible source of dark matter in the universe
E) the unseen member of a binary star system

Question 27

In what wavelength range was interferometry first routinely used?

A) radio
B) infrared
C) optical
D) ultraviolet
E) X-ray

Question 28

Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: Think about the laws of thermal radiation.)

A) The red star is more massive than the blue star.
B) The blue star is more massive than the red star.
C) The blue star is farther away than the red star.
D) The blue star has a hotter surface temperature than the red star.
E) The red star has a hotter surface temperature than the blue star.

Question 29

The atomic nuclei of the same element always have the same number of protons.

Question 30

In what part of the electromagnetic spectrum do the biggest telescopes on Earth operate?

A) radio
B) infrared
C) visible
D) ultraviolet
E) X-ray

Question 31

Spectra from neutral atoms compared with spectra from ionized atoms of the same element

A) are the same.
B) are slightly redshifted.
C) are slightly blueshifted.
D) have different sets of spectral lines.
E) have the same sets of spectral lines but different widths for those lines.

Question 32

Atomic nuclei consist of protons and electrons.

Question 33

From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 121.6 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 121.8 nm. What can we conclude?

A) The star is moving toward us.
B) The star is moving away from us.
C) The star is getting hotter.
D) The star is getting colder.
E) The "star" actually is a planet.

Question 34

When an electron in an atom goes from a higher energy state to a lower energy state, the atom

A) emits a photon of a specific frequency.
B) absorbs a photon of a specific frequency.
C) absorbs several photons of a specific frequency.
D) can emit a photon of any frequency.
E) can absorb a photon of any frequency.

Question 35

Which of the following wavelength regions cannot be studied with telescopes on the ground?

A) radio waves
B) ultraviolet
C) X-rays
D) both B and C
E) both A and C

Question 36

Which of the following objects is not a close approximation of a thermal emitter?

A) hot, thin gas
B) a star
C) a filament in a light bulb
D) you
E) a planet

Question 37

Electrons orbit an atomic nucleus like planets orbit the Sun.

Question 38

Currently, the largest optical telescope mirrors have a diameter of

A) 1 m.
B) 2 m.
C) 5 m.
D) 10 m.
E) 100 m.

Question 39

The largest effective telescope, created by radio interferometry, is the size of

A) several football fields, in a natural depression in Puerto Rico.
B) tens of miles across, in the deserts of New Mexico.
C) the state of New Mexico.
D) the continental United States.
E) Earth.

Question 40

Which of the following is not a good reason to place observatories on remote mountain tops?

A) to reduce light pollution
B) to reduce light distortion
C) to reduce light absorption
D) to be able to observe at radio wavelengths

Question 41

The energy levels for electrons vary from one element to another.

Question 42

Grass is green because it absorbs green light, reflecting all other colors.

Question 43

Any object moving relative to Earth will have a Doppler shift when viewed from Earth.

Question 44

A radio telescope and an optical telescope of the same size have the same angular resolution.

Question 45

The shorter the wavelength of light, the higher its frequency.

Question 46

The energy levels of an element and its ion are the same.

Question 47

Division of the EM Spectrum: The electromagnetic spectrum is divided into several parts that go by different names: radio waves, microwaves, infrared radiation, visible light, ultraviolet light, X-rays and Gamma-rays. However, we know that all are examples of the same phenomena, namely electromagnetic radiation. Why do you think these names were introduced in the first place? Research at your library or on reputable internet sites. Does retaining these names serve any useful purpose today?

Question 48

Most astronomical objects emit light over a broad range of wavelengths.

Question 49

Lines of a particular element appear at the same wavelength in both emission and absorption line spectra.

Question 50

You are currently emitting electromagnetic waves.

Question 51

X-rays are more intense than radio waves.

Question 52

Emission lines from different ionization states of the same element appear in the same place in the spectrum.

Question 53

World Observatories: In order to carry out new observations, modern astronomy requires access to highly specialized telescopes and instruments, be it telescopes in space such as the HST, or large collections of linked radio telescopes like the VLA. These facilities are so expensive to construct and maintain that we are entering an age in which only a single facility for each type of instrument will exist to serve the entire world. What do you think the impact of having only "world observatories" will be on the science of astronomy? Will it influence the scientific process? Should taxpayers be more willing to fund sciences like astronomy in order to avoid this situation?

Question 54

The greater the wavelength of light, the greater its energy.

Question 55

X-rays, because they have more energy, travel through space faster than visible light.

Question 56

Atomic number refers to ________.

Question 57

The Size of Molecules: You have a small flask of oil. You pour this oil onto a clear, calm pool of water and watch the oil slick spread out slowly with time. Imagine that it is your belief that the oil is not a continuous substance but made of individual particles called "molecules". Assuming this hypothesis is true, can you make a testable prediction on how the oil slick will behave as it spreads? Will this prediction allow you to estimate the size of the "molecules?" Search online to see if there is any evidence that the Greeks attempted such an experiment.

Question 58

The atomic nuclei of the same element always have the same number of neutrons.

Question 59

X-rays from astronomical objects can only be detected from telescopes in space.

Question 60

X-ray telescope mirrors are very similar to optical telescope mirrors.

Question 61

Explain what an interferometer is and give an example.

Question 62

An isotope of fluorine has 9 protons and 10 neutrons. What are the atomic number and atomic mass number of this fluorine? If we added a proton to this fluorine nucleus, would the result still be fluorine? What if we added a neutron instead? Explain.

Question 63

Explain how adaptive optics works.

Question 64

Explain why an absorption line spectrum is not filled back in (to make the original continuous spectrum) by the photons that are emitted as the excited electrons decay back down to their original energy levels.

Question 65

Draw and label a simple diagram of the following:
a. a refracting telescope
b. a reflecting telescope

Question 66

The most common isotope of oxygen has atomic number 8 and atomic mass number 16. Another isotope has two extra neutrons. What are the atomic number and atomic mass number of this isotope?

Question 67

Which transition, as shown, is not possible?

Question 68

State the two laws of thermal radiation.

Question 69

Define atomic mass number

Question 70

The resolution of a 10-meter telescope is about 0.01 arcsecond for visible light. Would you expect the actual angular resolution of a Keck 10-meter telescope in Hawaii to be better than, equal to, or worse than 0.01 arcsecond? Explain.

Question 71

Briefly explain how we can use spectral lines to determine an object's radial motion (toward or away from us). Can we also learn the object's tangential motion (across our line of sight) from its spectral lines?

Question 72

Which transition represents an electron that is breaking free of the atom?

Question 73

The most common isotope of gold has atomic number 79 and atomic mass number 197. How many protons and neutrons does the gold nucleus contain? Assuming the gold is electrically neutral, how many electrons does it have?

Question 74

Which transition represents the electron that emits a photon with the highest energy?

Question 75

Suppose the surface temperature of the Sun were about 18,000 K, rather than 6,000 K. How would the thermal radiation spectrum of the Sun be different?

Question 76

Briefly explain why spectral lines are useful in determining the chemical composition of their source.

Question 77

Suppose an astronomer proposed to build a major observatory on the campus of your school. Would it make a good observing site? Explain why or why not.

Question 78

The most common isotope of uranium is U-238, but the form used in nuclear bombs and nuclear power plants is U-235. Given that uranium has atomic number 92, how many neutrons are in each of these two isotopes?

Question 79

The resolution of a 10-meter telescope is about 0.01 arcsecond for visible light. Would you expect the angular resolution of a 10-meter radio telescope to be better than, equal to, or worse than 0.01 arcsecond? Explain.

Question 80

Which transition represents an electron that absorbs a photon with 10.2 eV of energy?