Copyright 2010 Pearson Education, Inc. Chapter 2 Light and
Matter
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Copyright 2010 Pearson Education, Inc.
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Chapter 2 Part One
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Copyright 2010 Pearson Education, Inc. 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
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Copyright 2010 Pearson Education, Inc. a) gamma rays b)
infrared c) sound d) visible light e) radio Which of these is NOT a
form of electromagnetic radiation? Question 1
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Copyright 2010 Pearson Education, Inc. a) gamma rays b)
infrared c) sound d) visible light e) radio Which of these is NOT a
form of electromagnetic radiation? Question 1 Sound comes from
pressure waves; all others are types of EM radiation of different
wavelengths.
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Copyright 2010 Pearson Education, Inc. 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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Copyright 2010 Pearson Education, Inc. 2.1 Information from the
Skies Wave motion: Transmission of energy without the physical
transport of material
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Copyright 2010 Pearson Education, Inc. 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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Copyright 2010 Pearson Education, Inc. 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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Copyright 2010 Pearson Education, Inc. 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 3x10 8 m/s = 660 nm / 2.2 x10 -15 s
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Copyright 2010 Pearson Education, Inc. What is the Frequency?
3x10 8 m/s = 660 nm / 2.2 x10 -15 s Period = 1 / Frequency
Frequency = 1 / period 1 / 2.2x10 -15 s = 4.54x10 14 Hz
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Copyright 2010 Pearson Education, Inc. a) wavelength b)
frequency c) period d) amplitude e) energy The distance between
successive wave crests defines the ________ of a wave. Question
2
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Copyright 2010 Pearson Education, Inc. a) wavelength b)
frequency c) period d) amplitude e) energy The distance between
successive wave crests defines the ________ of a wave. Question 2
Light can range from short- wavelength gamma rays to
long-wavelength radio waves.
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Copyright 2010 Pearson Education, Inc. 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
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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
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Copyright 2010 Pearson Education, Inc. 2.2 Waves in What?
Magnetic and electric fields are inextricably intertwined. A
magnetic field, such as the Earths shown here, exerts a force on a
moving charged particle.
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Copyright 2010 Pearson Education, Inc. 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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Copyright 2010 Pearson Education, Inc. 2.3 The Electromagnetic
Spectrum The visible spectrum is only a small part of the total
electromagnetic spectrum. Different colors of light are
distinguished by their frequency and wavelength.
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Copyright 2010 Pearson Education, Inc. 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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Copyright 2010 Pearson Education, Inc. 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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Copyright 2010 Pearson Education, Inc. a) radius. b) mass. c)
magnetic field. d) temperature. e) direction of motion. The
frequency at which a stars intensity is greatest depends directly
on its Question 3
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Copyright 2010 Pearson Education, Inc. a) radius. b) mass. c)
magnetic field. d) temperature. e) direction of motion. The
frequency at which a stars intensity is greatest depends directly
on its Question 3 Wiens Law means that hotter stars produce much
more high- frequency light.
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Copyright 2010 Pearson Education, Inc. 2.4 Thermal Radiation
Blackbody spectrum: Radiation emitted by an object depending only
on its temperature
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Copyright 2010 Pearson Education, Inc. 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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Copyright 2010 Pearson Education, Inc. 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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Copyright 2010 Pearson Education, Inc. Temperature vs.
Wavelength
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Copyright 2010 Pearson Education, Inc. 2.4 Thermal Radiation
Radiation laws: 2. Total energy emitted is proportional to fourth
power of temperature.
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Copyright 2010 Pearson Education, Inc. Question 4 a) cooler
than b) the same temperature as c) older than d) hotter than e)
more massive than The constellation ORION Rigel appears as a bright
bluish star, whereas Betelgeuse appears as a bright reddish star.
Rigel is ______ Betelgeuse. Betelgeuse Rigel
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Copyright 2010 Pearson Education, Inc. Question 4 Rigel appears
as a bright bluish star, whereas Betelgeuse appears as a bright
reddish star. Rigel is ______ Betelgeuse. The constellation ORION
Betelgeuse Rigel a) cooler than b) the same temperature as c) older
than d) hotter than e) more massive than Hotter stars look bluer in
color; cooler stars look redder.
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Copyright 2010 Pearson Education, Inc. Chapter 2 Part Two
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Copyright 2010 Pearson Education, Inc. First exam on September
14 th, 2011 Mastering Astronomy 50 unregistered students 4:00 PM to
5:30 PM Class ID MAMILLER18823
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Copyright 2010 Pearson Education, Inc. i>clickers 20
unregistered clickers 50 unregistered students Great clicker
shortage of 2011
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Copyright 2010 Pearson Education, Inc. Supernova SN2011fe
Brightness of a Billion Suns Coming to a Galaxy near you!
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Copyright 2010 Pearson Education, Inc. Look at the Big Dipper
with a small telescope or binoculars
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Copyright 2010 Pearson Education, Inc. Spectroscopy
Spectroscope: Splits light into component colors
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Copyright 2010 Pearson Education, Inc. Spectroscopy Emission
lines: Single frequencies emitted by particular atoms
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Copyright 2010 Pearson Education, Inc. Emission spectrum can be
used to identify elements. Spectroscopy
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Copyright 2010 Pearson Education, Inc. Absorption spectrum: If
a continuous spectrum passes through a cool gas, atoms of the gas
will absorb the same frequencies they emit. Spectroscopy
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Copyright 2010 Pearson Education, Inc. Spectroscopy Absorption
spectrum of the Sun
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Copyright 2010 Pearson Education, Inc. Kirchhoffs 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.
Spectroscopy
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Copyright 2010 Pearson Education, Inc. Kirchhoffs laws
illustrated Spectroscopy
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Copyright 2010 Pearson Education, Inc. 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. The Formation of Spectral Lines
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Copyright 2010 Pearson Education, Inc. Bohr Model
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Copyright 2010 Pearson Education, Inc. Emission energies
correspond to energy differences between allowed levels. Modern
model has electron cloud rather than orbit. The Formation of
Spectral Lines
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Copyright 2010 Pearson Education, Inc. 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.
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Copyright 2010 Pearson Education, Inc. 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.
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Copyright 2010 Pearson Education, Inc. Excited State 1 Excited
State 2
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Copyright 2010 Pearson Education, Inc. Excitation
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Copyright 2010 Pearson Education, Inc. Excitation
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Copyright 2010 Pearson Education, Inc. 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
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Copyright 2010 Pearson Education, Inc. 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.
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Copyright 2010 Pearson Education, Inc. Atomic excitation leads
to emission. (a) Direct decay (b) Cascade The Formation of Spectral
Lines
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Copyright 2010 Pearson Education, Inc. 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. The Formation of
Spectral Lines
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Copyright 2010 Pearson Education, Inc. Molecular spectra are
much more complex than atomic spectra, even for hydrogen. (a)
Molecular hydrogen(b) Atomic hydrogen The Formation of Spectral
Lines
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Copyright 2010 Pearson Education, Inc. 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. If a light
source is approaching you, you will observe Question 3
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Copyright 2010 Pearson Education, Inc. 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. If a light
source is approaching you, you will observe Question 3 The Doppler
Shift explains that wavelengths from sources approaching us are
blueshifted.
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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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Copyright 2010 Pearson Education, Inc. Depends only on the
relative motion of source and observer The Doppler Effect
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Copyright 2010 Pearson Education, Inc. The Doppler Effect The
Doppler effect shifts an objects entire spectrum either toward the
red or toward the blue.
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Copyright 2010 Pearson Education, Inc. Question 4 Analyzing a
stars spectral lines can tell us about all of these EXCEPT a) its
composition. b) its surface temperature. c) its transverse
(side-to- side) motion. d) its rotation. e) its density.
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Copyright 2010 Pearson Education, Inc. Question 4 Analyzing a
stars spectral lines can tell us about all of these EXCEPT a) its
composition. b) its surface temperature. c) its transverse
(side-to- side) motion. d) its rotation. e) its density. Only
motion toward or away from us influences a stars spectral lines.
Spectra can also tell us about a stars magnetic field.
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Copyright 2010 Pearson Education, Inc. Question 5 What types of
electro- magnetic 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
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Copyright 2010 Pearson Education, Inc. Question 5 What types of
electro- magnetic 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 Earths atmosphere allows radio
waves and visible light to reach the ground.
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Copyright 2010 Pearson Education, Inc. Equations and Symbols
Wavelength = Lambda) meters (m) Velocity = (Nu) meters/second
Frequency = f Hz or 1/s Period = secondss Speed of light = c3x10 8
m/s
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Copyright 2010 Pearson Education, Inc. Basic Equations = fm/s =
m x 1/s f = / 1/s = (m/s) / m = /fm = (m/s) / 1/s
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Copyright 2010 Pearson Education, Inc. Example Radio signals
travel at the speed of light. What is the wavelength of a radio
signal at 1MHz? (M = million) = /fm = (m/s) / 1/s A.1 m B.3 m C.100
m D.300 m
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Copyright 2010 Pearson Education, Inc. D. 300 m = /f M = (m/s)
/ 1/s 300 m = 3x10 8 m/s / 1x10 6 /s
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Copyright 2010 Pearson Education, Inc.
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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 Awaxing crescent.
Bwaning crescent. Cfull. Dthird quarter. Efirst quarter.
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Copyright 2010 Pearson Education, Inc. The fact that the Earth
has moved along its orbit in the time it took to rotate once is the
reason for A the difference between solar and sidereal time.
Bprecession. CEarth's 23.5-degree tilt. Dseasons. Ethe position of
the Celestial Equator. Completed
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Copyright 2010 Pearson Education, Inc. Latitude and right
ascension are coordinate systems used to find objects on the
Celestial Sphere. A True B False
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Copyright 2010 Pearson Education, Inc. A planet whose distance
from the Sun is 3 A.U. would have an orbital period of how many
Earth-years? A 3 B Square root 27 C 81 D 9 E Square root of 9 p 2 =
a 3 p 2 = 3 3 p 2 = 27 p = square root 27
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Copyright 2010 Pearson Education, Inc. AThe amplitude is 6 and
the wavelength is 4. BThe amplitude is 8 and the wavelength is 12.
CThe amplitude is 4 and the wavelength is 12. DThe amplitude is 8
and the wavelength is 6. EThe amplitude is 4 and the wavelength is
6. Completed Consider this diagram. Which statement is true?
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Copyright 2010 Pearson Education, Inc. Summary of Chapter 2
Wave: period, wavelength, amplitude Electromagnetic waves created
by accelerating charges Visible spectrum is different wavelengths
of light. Entire electromagnetic spectrum: includes radio waves,
infrared, visible light, ultraviolet, X-rays, gamma rays can tell
the temperature of an object by measuring its blackbody
radiation
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Copyright 2010 Pearson Education, Inc. Summary of Chapter 2,
cont. Spectroscope splits light beam into component frequencies.
Continuous spectrum is emitted by solid, liquid, and dense gas. Hot
gas has characteristic emission spectrum. Continuous spectrum
incident on cool, thin gas gives characteristic absorption
spectrum.
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Copyright 2010 Pearson Education, Inc. Summary of Chapter 2,
cont. Spectra can be explained using atomic models, with electrons
occupying specific orbitals. Emission and absorption lines result
from transitions between orbitals. Doppler effect can change
perceived frequency of radiation. Doppler effect depends on
relative speed of source and observer.