Astronomy Ch 5
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You know the frequency of a photon and the speed of light. What else can you determine about the photon?
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Wavelength and energy
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What best describes the fundamental difference between two different chemical elements?
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They have different numbers of protons in their nucleus
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If we say that a material is opaque to ultraviolet, we mean that it _____.
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Absorbs ultraviolet light
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What type of visible light spectrum does the sun produce?
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An absorption line spectrum
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Which forms of light are LOWER in energy and frequency than the light that our eyes can see?
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Infrared and radio
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Thermal radiation is defined as what?
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Radiation with a spectrum whose shape depends only on the temp of the emitting object
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According to the laws of thermal radiation, hotter objects emit photons with what?
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A shorter average wavelength
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Suppose you want to know the chemical composition of a distant star. Which piece of info is most useful to you?
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The wavelength of spectral lines in the stars spectrum
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The spectra of most galaxies show redshifts. This means that their spectral lines _____.
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Have wavelengths that are longer than normal.
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If you had only one telescope and wanted to take both visible light and ultraviolet pictures of stars where should you locate your telescope?
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In space
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What best describes the two principle advantages of telescopes over eyes?
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Telescopes can collect far more light with far better angular resolution
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The stars in our sky twinkle because of what?
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Turbulence in earths atmosphere
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What best describes why we say that light is an electromagnetic wave?
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The passage of a light wave can cause electrically charged particles to move up and down
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What is not true about x-Rays and radio waves?
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X-Rays travel through space faster than radio waves
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Suppose you built a scale model atom in which the nucleus is the size of a tennis ball. About how far would the cloud of electrons extend?
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Several kilometers
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What is true of green grass?
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It absorbs red light and reflects green light
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What condition leads you to see an absorption line spectrum from a cloud of gas in interstellar space?
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The cloud is cool and lies between you and a hot star
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What is ALWAYS true about thermal radiation?
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A hot object emits more radiation per unit surface area than a cool object
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Lab measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers. A particular stars spectrum shows the same hydrogen line at a wavelength of 486.0 nanometers. What can we conclude?
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The star is moving toward us
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Suppose star X and star Y both have redshifts. But star X has a larger redshift than star Y. What can you conclude?
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Star X is moving away from us faster than star Y
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What is NOT an advantage of the Hubble space telescope over ground based telescopes?
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Is it closer to the stars
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The Chandra X-Ray observatory must operate in space because of what?
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X-Rays do not penetrate earths atmosphere.
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What is always true about images captured by X-ray telescopes?
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They are always shown with colors that are not the true colors of the objects that were photographed
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From shortest to longest wavelength
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Gamma rays, x-Rays, ultraviolet, visible light, infrared, radio
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When considering light as made up of individual pieces, each characterized by a particular amount of energy, the pieces are called what?
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Photons
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6 protons and 7 neutrons. What is the atomic number and atomic mass number?
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Atomic number = 6 Atomic mass number = 13
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Visible light from a distant star can be spread into a spectrum by using a glass prism or ____.
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A diffraction grating
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Suppose you look at a spectrum of visible light by looking through a prism or diffraction grating. How can you decide whether it is an emission line spectrum or an absorption line spectrum?
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An emission line spectrum consists of bright lines on a dark background. An absorption line spectrum consists of dark lines on a rainbow background
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An atom that has fewer electrons that protons is called a what?
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Ion
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According to the laws of thermal radiation, hotter objects emit photons with ____.
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A shorter average wavelength.
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What is the angular resolution of the human eye?
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About 1 arcminute, or 1/60 of a degree
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What is the purpose of interferometry?
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It allows two or more small telescopes to achieve the angular resolution of a much larger telescope
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How are wavelength, frequency, and energy related for photons of light?
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Longer wavelength means lower frequency and lower energy
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How many atoms fit across the period at the end of a sentence?
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Millions
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Compared to the size of its nucleus, the size of an atom is about ____.
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One hundred thousand times greater
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What is true about electrical charge?
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A positive charge and a negative charge will attract each other
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What is NOT true about electrons?
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Electrons orbit the nucleus rather like planets orbiting the sun
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Atomic number is 26 and atomic mass number 56. If it is neutral, how many protons, neutrons, and electrons does it have?
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26 protons. 30 neutrons. 26 electrons
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When an atom loses and electron it becomes what?
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Ionized
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An electron-volt is what?
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An amount of energy much smaller than a joule
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How can an electron in an atom lose energy to go from a higher energy level to a lower energy level?
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It releases a photon equal in energy to its own energy drop
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We can see each other in the classroom because we ____.
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Reflect visible light
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When an electron in an atom goes from a higher energy state to a lower energy state, the atom
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Emits a photon of a specific frequency
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Spectra from neutral atoms compared with spectra from ionized atoms of the same element
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Have different sets of spectral lines
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What is ALWAYS true about thermal radiation?
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A hot object emits photons with a higher average energy than a cool object
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A gas heated to million of degrees would emit what?
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Mostly x-rays
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What is an artificial star?
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A point of light in earths atmosphere created by a laser for the purposes of monitoring atmospheric fluctuations
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Currently, the largest optical telescope mirrors have a diameter of what?
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10 m
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The largest effective telescope is the diameter of
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Earth
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In what wavelength range was interferometry first routinely used?
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Radio
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A typical atom has a size of about
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1 Angstrom
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When an electron drops to a lower energy level in an atom ____.
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Light at a wavelength specific to the change in energy levels is emitted
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What describes the light that can be detected from a person?
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The person reflects many wavelengths of visible light and emits a continuum of wavelengths of infrared light
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What telescope is best suited for studying the hottest intergalactic gas in a cluster of galaxies?
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Chandra X-Ray Telescope
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What observational technique is most appropriate for measuring Doppler shifts?
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Spectroscopy
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Compare the energy and speed of infrared and visible light. What is true?
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Visible light has higher energy but the same speed.
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Cell phone signals passing through walls is an example of what?
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Transmission
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White light hitting white paper is an example of what?
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Reflection or scattering
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What cannot be determined from a spectrum of a star?
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Speed perpendicular to my line of sight.
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There are more atoms in a glass of water than stars in the observable universe.
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True
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Atomic nuclei consist of protons and electrons.
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False
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Electrons orbit an atomic nucleus that planets orbit the sun.
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False
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The atomic nuclei of the same element always have the same number of protons.
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True
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The atomic nuclei of the same element always have the same number of neutrons
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False
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The energy levels for electrons vary from one element to another.
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True
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The energy levels of an element and it's ions are the same
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False
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The shorter the wavelength of light, the higher its frequency
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True
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X-Rays, because they have more energy, travel through space faster than visible light
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False
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X-Rays are more intense than radio waves
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False
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You are currently emitting electromagnetic waves
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True
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Lines of a particular element appear at the same wavelength in both emission and absorption line spectra.
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True
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Any object moving relative to earth will have a Doppler shift when viewed from earth.
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False
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Emission lines from different ionization states of the same element appear in the same place in the spectrum.
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False
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Most astronomical objects emit light over a broad range of wavelengths
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True
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A radio telescope and an optical telescope of the same size have the same angular resolution.
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False
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X-ray telescope mirrors are very similar to optical telescope mirrors
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False
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A blue camera filter appears blue because it transmits blue light, absorbing all other colors
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True
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When atoms of an element are heated enough that they lose electrons, their emission and absorption spectra change
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True
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Any object moving towards or away from earth will show a Doppler shift when observed from earth
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True
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What is NOT a good reason to place observatories on remote mountain tops?
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To be able to observe at radio wavelengths
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Grass is green because it absorbs green light reflecting all other colors.
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False
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X-rays from astronomical objects can only be detected from telescopes in space
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True
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What cannot be studied with telescopes on the ground?
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X-rays and untraviolet
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Why is earths daytime sky blue?
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Molecules scatter blue light more than red light
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The greater wavelengths of light, the greater the energy
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False
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What is the purpose of adaptive optics?
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It reduces blurring caused by atmospheric turbulence for telescopes on the ground
