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Transcript
1 QUIZ 1 - AY5-S13 . . . . . . . . . . . . . . . . . YOUR NAME: Possibly useful formulae: λmax (cm) = 0.29 T(K) ; λ × f = c (wavelength x frequency = speed); Energy radiated per unit area = σ × T(K)4 Speed of light = c = 300,000 km/sec 1. How long does it take light to travel from the Moon to the Earth, a distance of 384,000 km? By the way, did you remember to write your name on the quiz? Time = distance/speed=(384,000km/300,000km/sec)=1.28 seconds 2. When does the new moon rise (the phase when you cannot see any of the illuminated half of the moon)? Draw a picture of the relative positions of the Moon, Sun and Earth that demonstrate your answer. Dawn. EARTH—-Moon—-SUN 3. Rank the following in order of increasing wavelength (1 - shortest; 4 - longest): 1 X-rays 4 FM radio (800 MegaHertz) 2 Blue light 3 Infrared 4. A source emits infrared radiation at a wavelength of 1060×10−9 m. What is the frequency of this radiation? f=c/λ = (3 × 105 km/sec)/(1060 × 10−9 m)× (1000m/1km) 5. Suppose you have a hot gas of hydrogen and a hot gas of helium, each at the same temperature. Label the following statements True (T) or False (F). F The two gases would have identical spectra F Both gases would show identical emission-line spectra T The two gases would show different emission-line spectra F Both would show continuous spectra, with the helium-gas spectrum peaking at a shorter wavelength 6. What color would a yellow banana slug appear if illuminated with white light? Yellow 2 7. Suppose you lived on the Moon where there is essentially no atmosphere. Label the following statements as (T)rue or (F)alse: F The Sun would appear redder (compared to as seen from the Earth) during the day. T The color of the sky (looking away from the Sun during the day) would be black. F At sunset, the Sun would appear redder than it does at noon. F The “green flash” would be a “red flash” 8. For a 2900K object, at what wavelength is the peak of the Planck radiation curve? λmax = 0.29/2900 (units of cm) 9. Based on the schematic diagram below of the allowed energy levels in an atom: B, C Which transition(s) correspond(s) to the absorption of a photon? A Which transition corresponds to the lowest energy photon emitted? D Which transition corresponds to the shortest wavelength energy photon emitted? A Which transition corresponds to the lowest frequency photon emitted? A D B C 10. Star A has twice the trigonometric parallax angle and twice the luminosity of Star B. (Assume no dust toward either star) a) What are the relative distances of the two stars? Star A has a larger parallax angle and is therefore closer than Star B. A is 1/2 the distance of B. b) what are the relative brightnesses of the two stars? Based on the relative distances, Star A would be 4x brighter than Star B (inverse square law). Based on the relative luminosities, Star A would be twice as bright. In combination, Star A would be 4 x 2 = 8 times brighter than Star B