Midterm 1 Wednesday 18 Feb 2010 Chapters 1 4 Bring Scantron page 2 pencil to throw at the teacher Will not take the full period Relax Copyright 2009 Pearson Education Inc Copyright 2009 Pearson Education Inc How many of you have seen a Sun Dog A Yeah B Nope C I have no idea what the heck you are talking about D I don t do drugs E My roommate has but he also thinks he was abducted by aliens Copyright 2009 Pearson Education Inc Sun Dogs Copyright 2009 Pearson Education Inc Sundog Mystery Copyright 2009 Pearson Education Inc Chapter 5 Light The Cosmic Messenger Copyright 2009 Pearson Education Inc 5 1 Basic Properties of Light and Matter Our goals for learning What is light What is matter How do light and matter interact Copyright 2009 Pearson Education Inc What is light Copyright 2009 Pearson Education Inc Copyright 2009 Pearson Education Inc Light is an electromagnetic wave Copyright 2009 Pearson Education Inc Anatomy of a Wave Copyright 2009 Pearson Education Inc Wavelength and Frequency wavelength frequency speed of light constant Copyright 2009 Pearson Education Inc The Electromagnetic Spectrum Electromagnetic Spectrum Copyright 2009 Pearson Education Inc 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 Copyright 2009 Pearson Education Inc Wavelength Frequency and Energy l f c l wavelength f frequency c 3 00 108 m s speed of light E h f photon energy h 6 626 10 34 joule s photon energy Copyright 2009 Pearson Education Inc Thought Question The higher the photon energy A the longer its wavelength B the shorter its wavelength C Energy is independent of wavelength Copyright 2009 Pearson Education Inc Thought Question The higher the photon energy A the longer its wavelength B the shorter its wavelength C Energy is independent of wavelength Copyright 2009 Pearson Education Inc What is matter Copyright 2009 Pearson Education Inc Atomic Terminology Atomic Number of protons in nucleus Atomic Mass Number of protons neutrons Copyright 2009 Pearson Education Inc Atomic Terminology Isotope same of protons but different of neutrons 4He 3He Molecules consist of two or more atoms H2O CO2 Copyright 2009 Pearson Education Inc How do light and matter interact Emission Absorption Transmission Transparent objects transmit light Opaque objects block absorb light Reflection or scattering Copyright 2009 Pearson Education Inc Reflection and Scattering Mirror reflects light in a particular direction Copyright 2009 Pearson Education Inc Movie screen scatters light in all directions Interactions of Light with Matter Interactions between light and matter determine the appearance of everything around us Copyright 2009 Pearson Education Inc 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 E Because it is Republican Copyright 2009 Pearson Education Inc 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 Copyright 2009 Pearson Education Inc What have we learned What is light Light is a form of energy Light comes in many colors that combine to form white light Light is an electromagnetic wave that also comes in individual pieces called photons Each photon has a precise wavelength frequency and energy Forms of light are radio waves microwaves infrared visible light ultraviolet X rays and gamma rays What is matter Ordinary matter is made of atoms which are made of protons neutrons and electrons Copyright 2009 Pearson Education Inc What have we learned 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 Copyright 2009 Pearson Education Inc 5 2 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 Copyright 2009 Pearson Education Inc What are the three basic types of spectra Continuous Spectrum Emission Line Spectrum Absorption Line Spectrum Spectra of astrophysical objects are usually combinations of these three basic types Copyright 2009 Pearson Education Inc Introduction to Spectroscopy Copyright 2009 Pearson Education Inc Three Types of Spectra Illustrating Kirchhof s Laws Copyright 2009 Pearson Education Inc Continuous Spectrum The spectrum of a common incandescent light bulb spans all visible wavelengths without interruption Copyright 2009 Pearson Education Inc 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 Copyright 2009 Pearson Education Inc 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 Copyright 2009 Pearson Education Inc How does light tell us what things are made of Spectrum of the Sun Copyright 2009 Pearson Education Inc Chemical Fingerprints Each type of atom has a unique set of energy levels Each transition corresponds to a unique photon energy frequency and wavelength Energy levels of hydrogen Copyright 2009 Pearson Education Inc Chemical Fingerprints Downward transitions produce a unique pattern of emission lines Copyright 2009 Pearson Education Inc Production of Emission Lines Copyright 2009 Pearson Education Inc Chemical Fingerprints Because those atoms can absorb photons with those same energies upward transitions produce a pattern of absorption lines at the same wavelengths Copyright 2009 Pearson Education Inc Production of Absorption Lines Copyright 2009 Pearson Education Inc Production of Emission Lines Copyright 2009 Pearson Education Inc Chemical Fingerprints Each type of atom has a unique spectral fingerprint Copyright 2009 Pearson Education Inc Composition of a Mystery Gas Copyright 2009 Pearson Education Inc Chemical Fingerprints Observing the fingerprints in a spectrum tells us which kinds of atoms are present Copyright 2009 Pearson Education Inc Example Solar Spectrum Copyright 2009 Pearson Education Inc Thought Question Which letter s labels absorption lines A Copyright 2009 Pearson Education Inc B C D E
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