Presentation on theme: "Chapter 5 Light and Matter: Reading Messages from the Cosmos"— Presentation transcript:
1 Chapter 5 Light and Matter: Reading Messages from the Cosmos
2 5.1 Light in Everyday Life Our goals for learning: How do we experience light?How do light and matter interact?
3 How do we experience light? The warmth of sunlight tells us that light is a form of energyWe can measure the flow of energy in light in units of watts: 1 watt = 1 joule/s
4 Colors of Light White light is made up of many different colors Newton showed that white light is composed of all the colors of the rainbow.White light is made up of many different colors
5 How do light and matter interact? EmissionAbsorptionTransmissionTransparent objects transmit lightOpaque objects block (absorb) lightReflection or Scattering
6 Reflection and Scattering Mirror reflects light in a particular directionMovie screen scatters light in all directions
7 Interactions of Light with Matter Interactions between light and matter determine the appearance of everything around us
8 Thought Question Why is a rose red? The rose absorbs red light.The rose transmits red light.The rose emits red light.The rose reflects red light.
9 Thought Question Why is a rose red? The rose absorbs red light.The rose transmits red light.The rose emits red light.The rose reflects red light.
10 What have we learned? How do we experience light? Light is a form of energyLight comes in many colors that combine to form white light.How does light interact with matter?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.
11 5.2 Properties of Light Our goals for learning: What is light? What is the electromagnetic spectrum?
12 What is light? Light can act either like a wave or like a particle Particles of light are called photons
13 WavesA wave is a pattern of motion that can carry energy without carrying matter along with it
14 wave speed = wavelength x frequency Properties of WavesWavelength is the distance between two wave peaksFrequency is the number of times per second that a wave vibrates up and downwave speed = wavelength x frequency
15 Light: Electromagnetic Waves A light wave is a vibration of electric and magnetic fieldsLight interacts with charged particles through these electric and magnetic fields
16 Wavelength and Frequency wavelength x frequency = speed of light = constant
17 Particles of Light Particles of light are called photons Each photon has a wavelength and a frequencyThe energy of a photon depends on its frequency
18 Wavelength, Frequency, and Energy l x f = cl = wavelength , f = frequencyc = 3.00 x 108 m/s = speed of lightE = h x f = photon energyh = x joule x s = photon energy
20 The Electromagnetic Spectrum Use this tool from the Light and Spectroscopy tutorial to go over the inverse relationship between wavelength and frequency.
21 Thought Question The higher the photon energy… the longer its wavelength.the shorter its wavelength.energy is independent of wavelength.
22 Thought Question The higher the photon energy… the longer its wavelength.the shorter its wavelength.energy is independent of wavelength.
23 What have we learned? What is light? Light can behave like either a wave or a particleA light wave is a vibration of electric and magnetic fieldsLight waves have a wavelength and a frequencyPhotons 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.
24 5.3 Properties of Matter Our goals for learning: What is the structure of matter?What are the phases of matterHow is energy stored in atoms?
25 What is the structure of matter? ElectronCloudNucleusAtomUse this figure to define the nucleus; protons, neutrons, electrons; scale of atom and “electron cloud.”
26 Atomic Terminology Atomic Number = # of protons in nucleus Atomic Mass Number = # of protons + neutronsMolecules: consist of two or more atoms (H2O, CO2)
27 Atomic TerminologyIsotope: same # of protons but different # of neutrons. (4He, 3He)
28 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
29 Phases of WaterNewton showed that white light is composed of all the colors of the rainbow.
30 Phase ChangesIonization: Stripping of electrons, changing atoms into plasmaDissociation: Breaking of molecules into atomsEvaporation: Breaking of flexible chemical bonds, changing liquid into solidMelting: Breaking of rigid chemical bonds, changing solid into liquid
31 How is energy stored in atoms? Excited StatesGround StateElectrons in atoms are restricted to particular energy levels
32 Energy Level Transitions The only allowed changes in energy are those corresponding to a transition between energy levelsNot AllowedAllowed
33 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 electronsWhat 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 atomsStripping of electrons from atoms (ionization) turns the substance into a plasma
34 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 amount corresponding to particular changes in energy levels.
35 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?
36 What are the three basic types of spectra? Continuous SpectrumEmission Line SpectrumAbsorption Line SpectrumSpectra of astrophysical objects are usually combinations of these three basic types
37 This tool from the Light and Spectroscopy tutorial.
39 Continuous SpectrumThe spectrum of a common (incandescent) light bulb spans all visible wavelengths, without interruption
40 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
41 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
42 How does light tell us what things are made of? Spectrum of the Sun
43 Chemical Fingerprints Each type of atom has a unique set of energy levelsEach transition corresponds to a unique photon energy, frequency, and wavelengthEnergy levels of Hydrogen
44 Chemical Fingerprints Downward transitions produce a unique pattern of emission lines
45 This tool from the Light and Spectroscopy tutorial.
46 Chemical Fingerprints Because those atoms can absorb photons with those same energies, upward transitions produce a pattern of absorption lines at the same wavelengths
47 This tool from the Light and Spectroscopy tutorial.
48 This tool from the Light and Spectroscopy tutorial.
49 Chemical Fingerprints Each type of atom has a unique spectral fingerprint
50 This tool from the Light and Spectroscopy tutorial This tool from the Light and Spectroscopy tutorial. Use it to show unique chemical fingerprints.
51 Chemical Fingerprints Observing the fingerprints in a spectrum tells us which kinds of atoms are present
52 Example: Solar Spectrum 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.
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 complicatedMany of these molecular transitions are in the infrared part of the spectrum
55 What have we learned? What are the three basic type of spectra? Continuous spectrum, emission line spectrum, absorption line spectrumHow 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.