Download Copyright © 2010 Pearson Education, Inc. Chapter 2 Light and Matter
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Download Download Copyright © 2010 Pearson Education, Inc. Chapter 2 Light and Matter...
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Chapter 2
Light and Matter
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Chapter 2 Part One
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Ideas in Chapter 2 Information from the Skies Waves in What? The Electromagnetic Spectrum Thermal Radiation
Spectroscopy The Formation of Spectral Lines
The Doppler Effect Copyright © 2010 Pearson Education, Inc.
Question 1 Which of these is NOT a form of electromagnetic radiation?
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a) gamma rays b) infrared c) sound d) visible light e) radio
Question 1 Which of these is NOT a form of electromagnetic radiation?
a) gamma rays b) infrared c) sound d) visible light e) radio
Sound comes from pressure waves; all others are types of EM radiation of different wavelengths.
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2.1 Information from the Skies Electromagnetic radiation: Transmission of energy through space without physical connection through varying electric and magnetic fields Example: Light
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2.1 Information from the Skies Wave motion: Transmission of energy without the physical transport of material
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2.1 Information from the Skies Example: Water wave Water just moves up and down.
Wave travels and can transmit energy.
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2.1 Information from the Skies Frequency: Number of wave crests that pass a given point per second units of Hertz (Hz) Period: Time between passage of successive crests Relationship: Period = 1 / Frequency Wave with frequency of 1000 Hz
Period = 1/1000 Hz 0.001 s or 1 ms
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2.1 Information from the Skies Wavelength: Distance between successive crests Velocity: Speed at which crests move
Relationship: Velocity = Wavelength / Period 1 m/s = 1 m / 1 s 3x108 m/s = 660 nm / 2.2 x10-15 s
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What is the Frequency? 3x108 m/s = 660 nm / 2.2 x10-15 s Period = 1 / Frequency Frequency = 1 / period 1 / 2.2x10-15 s = 4.54x1014 Hz
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Question 2 The distance between successive wave crests defines the ________ of a wave.
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a) wavelength b) frequency c) period d) amplitude e) energy
Question 2 The distance between successive wave crests defines the ________ of a wave.
a) wavelength b) frequency c) period d) amplitude e) energy
Light can range from shortwavelength gamma rays to long-wavelength radio waves.
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2.2 Waves in What? Diffraction: The bending of a wave around an obstacle
Interference: The sum of two waves; may be larger or smaller than the original waves Copyright © 2010 Pearson Education, Inc.
2.2 Waves in What? Water waves, sound waves, and so on, travel in a medium (water, air, …). Electromagnetic waves need no medium. Created by accelerating charged particles Copyright © 2010 Pearson Education, Inc.
2.2 Waves in What? Magnetic and electric fields are inextricably intertwined. A magnetic field, such as the Earth’s shown here, exerts a force on a moving charged particle.
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2.2 Waves in What? Electromagnetic waves: Oscillating electric and magnetic fields; changing electric field creates magnetic field, and vice versa
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2.3 The Electromagnetic Spectrum Different colors of light are distinguished by their frequency and wavelength. The visible spectrum is only a small part of the total electromagnetic spectrum.
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2.3 The Electromagnetic Spectrum Different parts of the full electromagnetic spectrum have different names, but there is no limit on possible wavelengths.
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2.3 The Electromagnetic Spectrum The atmosphere is only transparent at a few wavelengths – the visible, the near infrared, and the part of the radio spectrum with frequencies higher than the AM band. This means that our atmosphere is absorbing a lot of the electromagnetic radiation impinging on it, and also that astronomy at other wavelengths must be done above the atmosphere.
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Question 3 The frequency at which a star’s intensity is greatest depends directly on its
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a) radius. b) mass. c) magnetic field. d) temperature. e) direction of motion.
Question 3 The frequency at which a star’s intensity is greatest depends directly on its
Wien’s Law means that hotter stars produce much more highfrequency light.
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a) radius. b) mass. c) magnetic field. d) temperature. e) direction of motion.
2.4 Thermal Radiation Blackbody spectrum: Radiation emitted by an object depending only on its temperature
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The Kelvin Temperature Scale Kelvin temperature scale: • All thermal motion ceases at 0 K. • Water freezes at 273 K and boils at 373 K.
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2.4 Thermal Radiation Radiation laws: 1. Peak wavelength is inversely proportional to temperature. The higher the temperature the shorter the wavelength
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Temperature vs. Wavelength
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2.4 Thermal Radiation Radiation laws: 2. Total energy emitted is proportional to fourth power of temperature.
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Question 4 Rigel appears as a bright bluish star, whereas Betelgeuse appears as a bright reddish star. Rigel is ______ Betelgeuse.
Betelgeuse
The constellation ORION Rigel Copyright © 2010 Pearson Education, Inc.
a) cooler than b) the same temperature as c) older than d) hotter than e) more massive than
Question 4 Rigel appears as a bright bluish star, whereas Betelgeuse appears as a bright reddish star. Rigel is ______ Betelgeuse.
a) cooler than b) the same temperature as c) older than d) hotter than e) more massive than
Betelgeuse
The constellation ORION Rigel Copyright © 2010 Pearson Education, Inc.
Hotter stars look bluer in color; cooler stars look redder.
Chapter 2 Part Two
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First exam on September 14th, 2011
Mastering Astronomy 50 unregistered students 4:00 PM to 5:30 PM Class ID MAMILLER18823 Copyright © 2010 Pearson Education, Inc.
i>clickers 20 unregistered clickers
50 unregistered students Great clicker shortage of 2011
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Supernova SN2011fe Brightness of a Billion Suns Coming to a Galaxy near you!
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Look at the Big Dipper with a small telescope or binoculars
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Spectroscopy Spectroscope: Splits light into component colors
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Spectroscopy Emission lines: Single frequencies emitted by particular atoms
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Spectroscopy Emission spectrum can be used to identify elements.
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Spectroscopy Absorption spectrum: If a continuous spectrum passes through a cool gas, atoms of the gas will absorb the same frequencies they emit.
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Spectroscopy Absorption spectrum of the Sun
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Spectroscopy Kirchhoff’s laws: • Luminous solid, liquid, or dense gas produces continuous spectrum.
• Low-density hot gas produces emission spectrum. • Continuous spectrum incident on cool, thin gas produces absorption spectrum.
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Spectroscopy
Kirchhoff’s laws illustrated
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The Formation of Spectral Lines Existence of spectral lines required new model of atom, so that only certain amounts of energy could be emitted or absorbed. Bohr model had certain allowed orbits for electron.
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Bohr Model
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The Formation of Spectral Lines Emission energies correspond to energy differences between allowed levels. Modern model has electron “cloud” rather than orbit.
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Question 1 The wavelengths of emission lines produced by an element
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a) depend on its temperature. b) are identical to its absorption lines. c) depend on its density. d) are different than its absorption lines. e) depend on its intensity.
Question 1 The wavelengths of emission lines produced by an element
a) depend on its temperature. b) are identical to its absorption lines. c) depend on its density. d) are different than its absorption lines. e) depend on its intensity.
Elements absorb or emit the same wavelengths of light based on their electron energy levels. Copyright © 2010 Pearson Education, Inc.
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Excited State 1 Excited State 2
Excitation
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Excitation
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Question 2 Which of the following has a fundamentally different nature than the other four?
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a) proton b) electron c) neutron d) atomic nucleus e) photon
Question 2 Which of the following has a fundamentally different nature than the other four?
a) proton b) electron c) neutron d) atomic nucleus e) photon
Photons are packages of light energy. Protons, neutrons, & electrons are particles of matter within an atomic nucleus. Copyright © 2010 Pearson Education, Inc.
The Formation of Spectral Lines Atomic excitation leads to emission.
(a) Direct decay
(b) Cascade Copyright © 2010 Pearson Education, Inc.
The Formation of Spectral Lines Absorption spectrum: Created when atoms absorb photons of right energy for excitation
Multielectron atoms: Much more complicated spectra, many more possible states Ionization changes energy levels. Copyright © 2010 Pearson Education, Inc.
The Formation of Spectral Lines Molecular spectra are much more complex than atomic spectra, even for hydrogen. (a) Molecular hydrogen
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(b) Atomic hydrogen
Question 3 If a light source is approaching you, you will observe
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a) its spectral lines are redshifted. b) the light is much brighter. c) its spectral lines are shorter in wavelength. d) the amplitude of its waves has increased. e) its photons have increased in speed.
Question 3 If a light source is approaching you, you will observe
a) its spectral lines are redshifted. b) the light is much brighter. c) its spectral lines are shorter in wavelength. d) the amplitude of its waves has increased. e) its photons have increased in speed.
The Doppler Shift explains that wavelengths from sources approaching us are blueshifted. Copyright © 2010 Pearson Education, Inc.
The Doppler Effect If one is moving toward a source of radiation, the wavelengths seem shorter; if moving away, they seem longer. Relationship between frequency and speed:
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The Doppler Effect Depends only on the relative motion of source and observer
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The Doppler Effect The Doppler effect shifts an object’s entire spectrum either toward the red or toward the blue.
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Question 4 Analyzing a star’s spectral lines can tell us about all of these EXCEPT
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a) its composition. b) its surface temperature. c) its transverse (side-toside) motion. d) its rotation. e) its density.
Question 4 Analyzing a star’s spectral lines can tell us about all of these EXCEPT
a) its composition. b) its surface temperature. c) its transverse (side-toside) motion. d) its rotation. e) its density.
Only motion toward or away from us influences a star’s spectral lines. Spectra can also tell us about a star’s magnetic field. Copyright © 2010 Pearson Education, Inc.
Question 5 What types of electromagnetic radiation from space reach the surface of Earth?
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a) radio & microwaves b) X rays & ultraviolet light c) infrared & gamma rays d) visible light & radio waves e) visible & ultraviolet light
Question 5 What types of electromagnetic radiation from space reach the surface of Earth?
a) radio & microwaves b) X rays & ultraviolet light c) infrared & gamma rays d) visible light & radio waves e) visible & ultraviolet light
Earth’s atmosphere allows radio waves and visible light to reach the ground.
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Equations and Symbols • • • • •
Wavelength = l (Lambda) meters (m) Velocity = n (Nu) meters/second Frequency = f Hz or 1/s Period = seconds s Speed of light = c 3x108 m/s
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Basic Equations n=lf f=n/l l = n /f
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m/s = m x 1/s 1/s = (m/s) / m m = (m/s) / 1/s
Example • Radio signals travel at the speed of light. • What is the wavelength of a radio signal at 1MHz? (M = million) l = n /f m = (m/s) / 1/s A. B. C. D.
1m 3m 100 m 300 m
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D. 300 m l = n /f • M = (m/s) / 1/s • 300 m = 3x108 m/s / 1x106/s
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Exam 1 Example Questions
If the Moon appears half lit, and is almost overhead about 6:00 AM, its phase is A B C D E
waxing crescent. waning crescent. full. third quarter. first quarter.
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The fact that the Earth has moved along its orbit in the time it took to rotate once is the reason for
A B C D E
the difference between solar and sidereal time. precession. Earth's 23.5-degree tilt. seasons. the position of the Celestial Equator.
Completed
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Latitude and right ascension are coordinate systems used to find objects on the Celestial Sphere. A True B False
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A planet whose distance from the Sun is 3 A.U. would have an orbital period of how many Earth-years?
A B C D E
3 Square root 27 81 9 Square root of 9 p2 = a3 p2 = 33 p2 = 27 p = square root 27
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Consider this diagram. Which statement is true?
A
The amplitude is 6 and the wavelength is 4.
B
The amplitude is 8 and the wavelength is 12.
C
The amplitude is 4 and the wavelength is 12.
D
The amplitude is 8 and the wavelength is 6.
E
The amplitude is 4 and the wavelength is 6.
Completed
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