Lec11-Feb24

Lec11-Feb24 - 2/24/10 Discussion QuesFon Astro 109...

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Unformatted text preview: 2/24/10 Discussion QuesFon Astro 109 Lecture 11: Light and Atoms Feb. 24 Which of the following can we not learn by studying the spectrum of a star or planet? A.  The temperature of the object. B.  The composiFon of the object’s atmosphere and/or surface. C.  The distance to the object. D.  The speed at which the object is moving toward or away from us. E.  The rate at which the object is rotaFng. Feb. 24 Blackbody spectrum Key Concepts •  emission line and absorpFon line spectra •  atomic structure •  spectral lines < ­> composiFon of a gas •  Doppler effect Feb. 24 Feb. 24 Spectrograph Feb. 24 Feb. 24 1 2/24/10 Bohr model for hydrogen Light and atoms photon = “par+cle” of light Feb. 24 Feb. 24 Hydrogen Balmer series energy, frequency, wavelength: E = hν = Feb. 24 hc λ Feb. 24 Discussion QuesFon In order to produce an emission line spectrum, atoms must A.  B.  C.  D.  E.  Feb. 24 be in interstellar space. have less energy than the ground state. be in an excited state. be in orbit around a planet or star. be in a molecule. Feb. 24 2 2/24/10 Doppler Effect Discussion QuesFon What is the main reason that different elements produce different emission line spectra? Different elements have different A.  B.  C.  D.  E.  sizes boiling points responses to heat arrangements of electron energy levels smells Feb. 24 Feb. 24 Discussion QuesFon Discussion QuesFon When I swing the Doppler ball around my head, what do I hear? If I were to swing the hydrogen lamp around like the Doppler ball, what would you see through the diffracFon graFng? A.  B.  C.  D.  the standard pitch a pitch higher than the standard pitch a pitch lower than the standard pitch a pitch that oscillates higher and lower than the standard pitch E.  nothing at all Feb. 24 A.  B.  C.  D.  A conFnuous spectrum. The emission lines would always shi[ slightly to the red. The emission lines would always shi[ slightly to the blue. The lines would shi[ to the red when the lamp is moving toward you, and to the blue when it is moving away. E.  The lines would shi[ to the blue when the lamp is moving toward you, and to the red when it is moving away. Feb. 24 Kirchhoff’s laws RefracFon Light travels at a slower speed in a dense substance. The index of refracFon characterizes how fast light moves in a dense substance, and how much it bends. Feb. 24 Feb. 24 3 2/24/10 Discussion QuesFon The Sun’s spectrum Think about the emission and absorpFon line spectra produced by a given gas cloud. Which of the following is true? A.  The emission lines are closer together than the absorpFon lines. B.  The emission lines are farther apart than the absorpFon lines. C.  The spacing between the emission lines is the same as the spacing between the absorpFon lines. D.  The pa]ern of emission lines is unrelated to the pa]ern of absorpFon lines. Feb. 24 Feb. 24 Chemical fingerprinFng Recap •  emission line and absorpFon line spectra •  atomic structure •  spectral lines < ­> composiFon of a gas •  Doppler effect Feb. 24 Feb. 24 HW quesFons Discussion QuesFon Which of the following can we not learn by studying the spectrum of a star or planet? A.  The temperature of the object. B.  The composiFon of the object’s atmosphere and/or surface. C.  The distance to the object. D.  The speed at which the object is moving toward or away from us. E.  The rate at which the object is rotaFng. Feb. 24 19. Explain how we know that atoms have massive, compact nuclei. 20.  (a) Describe the spectrum of hydrogen at visible wavelengths. (b) Explain how Bohr’s model of the atom accounts for the Balmer lines. 21. Why do different elements display different pa]erns of lines in their spectra? 22.  What is the Doppler effect? Why is it important to astronomers? Feb. 24 4 2/24/10 HW quesFons Rutherford sca]ering 32. In Figure 5 ­13 you can see two disFnct dark lines at the boundary between the orange and yellow parts of the Sun’s spectrum. The wavelengths of these dark lines are 588.99 and 589.59 nm. What do you conclude from this about the chemical composiFon of the Sun’s atmosphere? 37.  (a) Can a hydrogen atom in the ground state absorb an H ­alpha (Hα) photon? Explain why or why not. (b) Can a hydrogen atom in the n=2 state absorb a Lyman ­alpha (Lα) photon? Explain why or why not. 41. You are given a traffic Fcket for going through a red light (wavelength 700 nm). You tell the police officer that because you were approaching the light, the Doppler effect caused a blueshi[ that made the light appear green (wavelength 500 nm). How fast would you have had to be going for this to be true? Feb. 24 “It was almost as incredible as if you fired a fi<een ­inch shell at a piece of +ssue paper and it came back and hit you.” Feb. 24 Example: Doppler shi[ of a stoplight The Sun’s spectrum λ0 λobs = 700 nm (red) = 500 nm (green) ∆λ ⇒ = 200 nm ∆λ λ0 p. 113: “For example, if sodium is placed in the flame of a Bunsen burner … it displays an emission line spectrum with two closely spaced spectral lines at wavelengths of 588.99 and 589.59 nm, in the orange ­ yellow part of the spectrum.” = v v c = 3.0 × 105 km s−1 × 200 nm 700 nm = 8.6 × 104 km s−1 = 86, 000 km s−1 = 309 million km/hr = 190 million mph λ = 588.99 and 589.59 nm Feb. 24 Feb. 24 5 ...
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This note was uploaded on 09/15/2011 for the course PHYS 109 taught by Professor Pryor during the Spring '09 term at Rutgers.

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