05 lecture outline
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The document covers the interaction of light and matter, discussing light as energy, its properties, and the electromagnetic spectrum. It explains how light interacts with matter through processes like emission, absorption, and reflection, as well as how the analysis of light spectra reveals the composition and temperatures of astronomical objects. Key concepts include the behavior of light as both a wave and a particle, the significance of photons, and the application of the Doppler effect to determine the speed of distant objects.
05 lecture outline
- 1. Chapter 5 Lecture © 2014 Pearson Education, Inc. The Cosmic Perspective Seventh Edition Light and Matter: Reading Messages from the Cosmos
- 2. Light and Matter: Reading Messages from the Cosmos
- 3. 5.1 Light in Everyday Life • Our goals for learning: – How do we experience light? – How do light and matter interact?
- 4. How do we experience light? • The warmth of sunlight tells us that light is a form of energy. • We can measure the flow of energy in light in units of watts: 1 watt = 1 joule/s.
- 5. • White light is made up of many different colors. Colors of Light
- 6. How do light and matter interact? • Emission • Absorption • Transmission – Transparent objects transmit light. – Opaque objects block (absorb) light. • Reflection/scattering
- 7. • Mirror reflects light in a particular direction. • Movie screen scatters light in all directions. Reflection and Scattering
- 8. • Interactions between light and matter determine the appearance of everything around us. Interactions of Light with Matter
- 9. Thought Question Why is a rose red? A. The rose absorbs red light. B. The rose transmits red light. C. The rose emits red light. D. The rose reflects red light.
- 10. Thought Question Why is a rose red? A. The rose absorbs red light. B. The rose transmits red light. C. The rose emits red light. D. The rose reflects red light.
- 11. What have we learned? • How do we experience light? – Light is a form of energy. – Light comes in many colors that combine to form white light. • How do light and matter interact? – Matter can emit light, absorb light, transmit light, and reflect (or scatter) light. – Interactions between light and matter determine the appearance of everything we see.
- 12. 5.2 Properties of Light • Our goals for learning: – What is light? – What is the electromagnetic spectrum?
- 13. What is light? • Light can act either like a wave or like a particle. • Particles of light are called photons.
- 14. Waves • A wave is a pattern of motion that can carry energy without carrying matter along with it.
- 15. Properties of Waves • Wavelength is the distance between two wave peaks. • Frequency is the number of times per second that a wave vibrates up and down. Wave speed = wavelength x frequency
- 16. Light: Electromagnetic Waves • A light wave is a vibration of electric and magnetic fields. • Light interacts with charged particles through these electric and magnetic fields.
- 17. Wavelength and Frequency wavelength x frequency = speed of light = constant
- 18. Particles of Light • Particles of light are called photons. • Each photon has a wavelength and a frequency. • The energy of a photon depends on its frequency.
- 19. Wavelength, Frequency, and Energy λ x f = c λ = wavelength, f = frequency c = 3.00 x 108 m/s = speed of light E = h x f = photon energy h = 6.626 x 10-34 joule x s = Planck's constant
- 20. Special Topic: Polarized Sunglasses • Polarization describes the direction in which a light wave is vibrating. • Reflection can change the polarization of light. • Polarized sunglasses block light that reflects off of horizontal surfaces.
- 21. What is the electromagnetic spectrum?
- 23. Thought Question The higher the photon energy, A. the longer its wavelength. B. the shorter its wavelength. C. energy is independent of wavelength.
- 24. Thought Question The higher the photon energy, A. the longer its wavelength. B. the shorter its wavelength. C. energy is independent of wavelength.
- 25. What have we learned? • What is light? – Light can behave like either a wave or a particle. – A light wave is a vibration of electric and magnetic fields. – Light waves have a wavelength and a frequency. – Photons are particles of light. • What is the electromagnetic spectrum? – Human eyes cannot see most forms of light. – The entire range of wavelengths of light is known as the electromagnetic spectrum.
- 26. 5.3 Properties of Matter • Our goals for learning: – What is the structure of matter? – What are the phases of matter – How is energy stored in atoms?
- 27. What is the structure of matter?
- 28. • Atomic number = # of protons in nucleus • Atomic mass number = # of protons + neutrons • Molecules: consist of two or more atoms (H2O, CO2) Atomic Terminology
- 29. Atomic Terminology • Isotope: same # of protons but different # of neutrons (4 He, 3 He)
- 30. What are the phases of matter? • Familiar phases: – Solid (ice) – Liquid (water) – Gas (water vapor) • Phases of same material behave differently because of differences in chemical bonds.
- 31. Phase Changes • Ionization: stripping of electrons, changing atoms into plasma • Dissociation: breaking of molecules into atoms • Evaporation: breaking of flexible chemical bonds, changing liquid into solid • Melting: breaking of rigid chemical bonds, changing solid into liquid
- 32. Phases and Pressure • Phase of a substance depends on both temperature and pressure. • Often more than one phase is present.
- 33. Ground state Excited states How is energy stored in atoms? • Electrons in atoms are restricted to particular energy levels.
- 34. Energy Level Transitions • The only allowed changes in energy are those corresponding to a transition between energy levels. Not allowed Allowed
- 35. What have we learned? • What is the structure of matter? – Matter is made of atoms, which consist of a nucleus of protons and neutrons surrounded by a cloud of electrons. • What are the phases of matter? – Adding heat to a substance changes its phase by breaking chemical bonds. – As temperature rises, a substance transforms from a solid to a liquid to a gas, then the molecules can dissociate into atoms. – Stripping of electrons from atoms (ionization) turns the substance into a plasma.
- 36. What have we learned? • How is energy stored in atoms? – The energies of electrons in atoms correspond to particular energy levels. – Atoms gain and lose energy only in amounts corresponding to particular changes in energy levels.
- 37. 5.4 Learning from Light • Our goals for learning: – What are the three basic types of spectra? – How does light tell us what things are made of? – How does light tell us the temperatures of planets and stars? – How does light tell us the speed of a distant object?
- 38. • Spectra of astrophysical objects are usually combinations of these three basic types. What are the three basic types of spectra?
- 39. What are the three basic types of spectra?
- 40. Three Types of Spectra
- 41. Continuous Spectrum • The spectrum of a common (incandescent) light bulb spans all visible wavelengths, without interruption.
- 42. Emission Line Spectrum • A thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines.
- 43. Absorption Line Spectrum • A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum.
- 44. How does light tell us what things are made of?
- 45. Chemical Fingerprints • Each type of atom has a unique set of energy levels. • Each transition corresponds to a unique photon energy, frequency, and wavelength.
- 46. Chemical Fingerprints • Downward transitions produce a unique pattern of emission lines.
- 48. Chemical Fingerprints • Because those atoms can absorb photons with those same energies, upward transitions produce a pattern of absorption lines at the same wavelengths.
- 50. Chemical Fingerprints • Each type of atom has a unique spectral fingerprint.
- 51. Chemical Fingerprints • Observing the fingerprints in a spectrum tells us which kinds of atoms are present.
- 52. Chemical Fingerprints Example: Solar Spectrum
- 53. Energy Levels of Molecules • Molecules have additional energy levels because they can vibrate and rotate.
- 54. Energy Levels of Molecules • The large numbers of vibrational and rotational energy levels can make the spectra of molecules very complicated. • Many of these molecular transitions are in the infrared part of the spectrum.
- 55. Thought Question Which letter(s) label(s) absorption lines?
- 56. Thought Question Which letter(s) label(s) absorption lines?
- 57. Thought Question Which letter(s) label(s) the peak (greatest intensity) of infrared light?
- 58. Thought Question Which letter(s) label(s) the peak (greatest intensity) of infrared light?
- 59. Thought Question Which letter(s) label(s) emission lines?
- 60. Thought Question Which letter(s) label(s) emission lines?
- 61. How does light tell us the temperatures of planets and stars?
- 62. Thermal Radiation • Nearly all large or dense objects emit thermal radiation, including stars, planets, you. • An object's thermal radiation spectrum depends on only one property: its temperature.
- 63. 1. Hotter objects emit more light at all frequencies per unit area. 2. Hotter objects emit photons with a higher average energy. Properties of Thermal Radiation
- 64. Wien's Law
- 65. Thought Question Which is hottest? A. a blue star B. a red star C. a planet that emits only infrared light
- 66. Thought Question Which is hottest? A. a blue star B. a red star C. a planet that emits only infrared light
- 67. Thought Question Why don't we glow in the dark? A. People do not emit any kind of light. B. People only emit light that is invisible to our eyes. C. People are too small to emit enough light for us to see. D. People do not contain enough radioactive material.
- 68. Thought Question Why don't we glow in the dark? A. People do not emit any kind of light. B. People only emit light that is invisible to our eyes. C. People are too small to emit enough light for us to see. D. People do not contain enough radioactive material.
- 69. Example: How do we interpret an actual spectrum? • By carefully studying the features in a spectrum, we can learn a great deal about the object that created it.
- 70. Reflected sunlight: Continuous spectrum of visible light is like the Sun's except that some of the blue light has been absorbed— object must look red. What is this object?
- 71. Thermal radiation: Infrared spectrum peaks at a wavelength corresponding to a temperature of 225 K. What is this object?
- 72. Carbon dioxide: Absorption lines are the fingerprint of CO2 in the atmosphere. What is this object?
- 73. Ultraviolet emission lines: Indicate a hot upper atmosphere What is this object?
- 74. Mars! What is this object?
- 75. How does light tell us the speed of a distant object?
- 77. The Doppler Effect • Same for Light
- 78. Stationary Moving away Away faster Moving toward Toward faster Measuring the Shift • We generally measure the Doppler effect from shifts in the wavelengths of spectral lines.
- 79. Measuring the Shift • The amount of blueshift or redshift tells us an object's speed toward or away from us.
- 80. Measuring the Shift • Doppler shift tells us ONLY about the part of an object's motion toward or away from us:
- 81. Thought Question I measure a line in the lab at 500.7 nm. The same line in a star has wavelength 502.8 nm. What can I say about this star? A. It is moving away from me. B. It is moving toward me. C. It has unusually long spectral lines.
- 82. Thought Question I measure a line in the lab at 500.7 nm. The same line in a star has wavelength 502.8 nm. What can I say about this star? A. It is moving away from me. B. It is moving toward me. C. It has unusually long spectral lines.
- 83. Measuring the Shift • Measuring Redshift
- 84. Measuring the Shift • Measuring Redshift
- 85. Measuring the Shift • Measuring Velocity
- 86. Measuring the Shift • Measuring Velocity
- 87. Rotation Rates • Different Doppler shifts from different sides of a rotating object spread out its spectral lines.
- 88. Spectrum of a Rotating Object • Spectral lines are wider when an object rotates faster.
- 89. What have we learned? • What are the three basic type of spectra? – Continuous spectrum, emission line spectrum, absorption line spectrum • How does light tell us what things are made of? – Each atom has a unique fingerprint. – We can determine which atoms something is made of by looking for their fingerprints in the spectrum.
- 90. What have we learned? • How does light tell us the temperatures of planets and stars? – Nearly all large or dense objects emit a continuous spectrum that depends on temperature. – The spectrum of that thermal radiation tells us the object's temperature. • How does light tell us the speed of a distant object? – The Doppler effect tells us how fast an object is moving toward or away from us.
Editor's Notes
- #6: Newton showed that white light is composed of all the colors of the rainbow.
- #28: Use this figure to define the nucleus; protons, neutrons, electrons; scale of atom and "electron cloud."
- #40: This tool from the Light and Spectroscopy tutorial.
- #48: This tool from the Light and Spectroscopy tutorial.
- #50: This tool from the Light and Spectroscopy tutorial.
- #52: Note that students may not be familiar with the notation concerning ions, especially since the book does it slightly differently in the text than it does in this figure, (i.e. +2 vs. ++) so this may need to be explained.
- #53: You can use this slide as an example of real astronomical spectra made from a combination of the idealized types. Here we have the continuous (thermal) spectrum from the solar interior; dark absorption lines where the cooler solar atmosphere (photosphere) absorbs specific wavelengths of light.
- #64: Remind students that the intensity is per area; larger objects can emit more total light even if they are cooler.
- #65: Remind students that the intensity is per area; larger objects can emit more total light even if they are cooler.
- #76: This figure from the book can give an introduction to the Doppler effect.
- #77: This and the following slides are tools from the Doppler Effect tutorial.
- #84: More tools from the Doppler shift tutorial.