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4 Suppose two observers look at the spectrum of a cloud of gas in a laboratory; the first reports seeing emission lines and the second reports absorption lines. Explain. 1) Only the first observer sees the gas against a hot background 2) Only the second observer sees the gas against a hot background. 3) One observer is moving rapidly relative to the other. 4) The atoms in the gas are forming molecules.

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6 656 nm 486 nm 434 nm 410 nm

7 656 nm: red-orange 486 nm: blue 434 nm: indigo 410 nm: violet

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9 Atoms of different elements have unique spectral lines because each element 1) has atoms of a unique color. 2) has a unique set of neutrons. 3) has a unique set of electron orbits. 4) has unique photons.

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11 Atoms have particular associated spectral lines because 1) electrons have only certain allowed orbits. 2) light consists of waves. 3) light waves can show the Doppler effect. 4) speed of light in a vacuum is a constant.

12 In the Sun, the transition from level 4 to level 2 of hydrogen produces photons with a wavelength of 486.1nm. In a star twice as hot as the Sun, this transition would produce photons with 1) half that wavelength. 2) the same wavelength. 3) twice that wavelength. 4) four times that wavelength.

13 Here is the spectrum of a mystery star: Which elements are present? 1.Calcium only 2.Calcium and hydrogen 3.Magnesium and calcium 4.Calcium, hydrogen, and magnesium

14 Here is the spectrum of a mystery star: Which elements are present? 1.Calcium only 2.Calcium and hydrogen 3.Magnesium and hydrogen 4.Calcium, hydrogen, and magnesium

15 Decoding Cosmic Spectra

16 Here is the spectrum of a mystery star: Which elements are present? 1.Calcium, hydrogen, and magnesium 2.Calcium and hydrogen 3.Magnesium and hydrogen 4.All of them

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20 THE SPECTRAL SEQUENCE Class SpectrumColorTemperature O ionized and neutral helium, weakened hydrogen bluish31,500-49,000 K B neutral helium, stronger hydrogen blue-white10,000-31,500 K A strong hydrogen, ionized metals white ,000 K F weaker hydrogen, ionized metals yellowish white K G still weaker hydrogen, ionized and neutral metals yellowish K K weak hydrogen, neutral metals orange K M little or no hydrogen, neutral metals, molecules reddish K L no hydrogen, metallic hydrides, alkalai metals red-infrared K T methane bandsinfraredunder 1200 K

21 OBAFGKMLTOBAFGKMLT

22 Origins: Decoding Spectra of Light from Distant Galaxies Origins Hour 4, Back to the Beginning, Chapter 6


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