Copyright © 2010 Pearson Education, Inc. Chapter 2 Light and Matter
Copyright © 2010 Pearson Education, Inc.
Chapter 2 Part One
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
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
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.
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
Copyright © 2010 Pearson Education, Inc. 2.1 Information from the Skies Wave motion: Transmission of energy without the physical transport of material
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.
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 s or 1 ms
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 x s
Copyright © 2010 Pearson Education, Inc. What is the Frequency? 3x10 8 m/s = 660 nm / 2.2 x s Period = 1 / Frequency Frequency = 1 / period 1 / 2.2x s = 4.54x10 14 Hz
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
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.
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
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.
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
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.
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.
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.
Copyright © 2010 Pearson Education, Inc. a) radius. b) mass. c) magnetic field. d) temperature. e) direction of motion. The frequency at which a star’s intensity is greatest depends directly on its Question 3
Copyright © 2010 Pearson Education, Inc. a) radius. b) mass. c) magnetic field. d) temperature. e) direction of motion. The frequency at which a star’s intensity is greatest depends directly on its Question 3 Wien’s Law means that hotter stars produce much more high- frequency light.
Copyright © 2010 Pearson Education, Inc. 2.4 Thermal Radiation Blackbody spectrum: Radiation emitted by an object depending only on its temperature
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.
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
Copyright © 2010 Pearson Education, Inc. Temperature vs. Wavelength
Copyright © 2010 Pearson Education, Inc. 2.4 Thermal Radiation Radiation laws: 2. Total energy emitted is proportional to fourth power of temperature.
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
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.
Copyright © 2010 Pearson Education, Inc. Chapter 2 Part Two
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
Copyright © 2010 Pearson Education, Inc. i>clickers 20 unregistered clickers 50 unregistered students Great clicker shortage of 2011
Copyright © 2010 Pearson Education, Inc. Supernova SN2011fe Brightness of a Billion Suns Coming to a Galaxy near you!
Copyright © 2010 Pearson Education, Inc. Look at the Big Dipper with a small telescope or binoculars
Copyright © 2010 Pearson Education, Inc. Spectroscopy Spectroscope: Splits light into component colors
Copyright © 2010 Pearson Education, Inc. Spectroscopy Emission lines: Single frequencies emitted by particular atoms
Copyright © 2010 Pearson Education, Inc. Emission spectrum can be used to identify elements. Spectroscopy
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
Copyright © 2010 Pearson Education, Inc. Spectroscopy Absorption spectrum of the Sun
Copyright © 2010 Pearson Education, Inc. 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. Spectroscopy
Copyright © 2010 Pearson Education, Inc. Kirchhoff’s laws illustrated Spectroscopy
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
Copyright © 2010 Pearson Education, Inc. Bohr Model
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
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.
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.
Copyright © 2010 Pearson Education, Inc. Excited State 1 Excited State 2
Copyright © 2010 Pearson Education, Inc. Excitation
Copyright © 2010 Pearson Education, Inc. Excitation
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
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.
Copyright © 2010 Pearson Education, Inc. Atomic excitation leads to emission. (a) Direct decay (b) Cascade The Formation of Spectral Lines
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
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
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
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.
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:
Copyright © 2010 Pearson Education, Inc. Depends only on the relative motion of source and observer The Doppler Effect
Copyright © 2010 Pearson Education, Inc. The Doppler Effect The Doppler effect shifts an object’s entire spectrum either toward the red or toward the blue.
Copyright © 2010 Pearson Education, Inc. 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-to- side) motion. d) its rotation. e) its density.
Copyright © 2010 Pearson Education, Inc. 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-to- side) 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 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
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 Earth’s atmosphere allows radio waves and visible light to reach the ground.
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
Copyright © 2010 Pearson Education, Inc. Basic Equations = fm/s = m x 1/s f = / 1/s = (m/s) / m = /fm = (m/s) / 1/s
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
Copyright © 2010 Pearson Education, Inc. D. 300 m = /f M = (m/s) / 1/s 300 m = 3x10 8 m/s / 1x10 6 /s
Copyright © 2010 Pearson Education, Inc.
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.
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
Copyright © 2010 Pearson Education, Inc. Latitude and right ascension are coordinate systems used to find objects on the Celestial Sphere. A True B False
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
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?
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
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.
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.