10/29/2018. Chapter 7. Atoms Light and Spectra. Reminders. Topics For Today s Class. Hydrogen Atom. The Atom. Phys1411 Introductory Astronomy

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1 Phys1411 Introductory Astronomy Instructor: Dr. Goderya Chapter 7 Atoms Light and Spectra Reminders Topics For Today s Class Project 1 due November 12 th after and during Lab. Extra-credit Homework online. Atoms Electric Force Isotopes, Ion and Binding Energy Bohr Model Different Kinds of Atoms Interaction of Light and Matter Excitation of Atoms Heat and Temperature Radiation from Heated Objects Two Radiation Laws Electron (-) Protons (+) Nucleus The Atom Quarks Smallest part of matter Nucleus, Protons, Neutrons and Electrons The elementary particle Quark Symbol - Z X A Z = Atomic Number Number of protons A = Mass Number Neutrons Electron (-) Proton (+) Hydrogen Atom Nucleus 1H 1 One proton in the nucleus one electron orbiting the nucleus Symbol - 1 H 1 1

2 Helium Atom An Excited Atom Two proton and two neutrons in the nucleus Two electrons orbiting the nucleus Symbol - 2 He 4 2He 4 Incoming photon can be absorbed if it has the correct energy It causes the electron to jump to a higher energy level scienceonline.com Isotopes What Holds the Atom Together? Charles-Augustin de Coulomb Electrons in an atom are bound to the nucleus via an electric force called coulomb force wikipedia.com Apulsephysics.com What is an Ion? Ionization and Binding Energy An atom has lost one or more electrons How much energy is needed to keep the electron bind to the atom Chemistry-batz-wikispaces.com staff.orecity.k12.or.us 2

3 A Box Diagram of an Atom 2 nd energy level 1 st energy level Ground state -E 4 -E 3 -E 2 -E 1 n 4 n 3 n 2 n 1 The Energy of the electron orbits are quantized That is each orbit carries a discrete energy value The closer the orbit to the nucleus, the more negative is its energy value -E 1 < -E 2 < -E 3 < -E 4 A box diagram -E h n h The energy of each orbit can be calculated ev = electron Volts 1 ev = x J -E h n h Electron can jumps from a one orbit to another orbit, the change in energy is E = E h -E l The wavelength of emitted light can be calculated -E l n l -E l n l Spectral line -E h -E l n h n l Emission: (colored spectral lines) Transition from n h to n l level. E = E h -E l Absorption: (dark spectral line) Transition from n h to n l level. The spectrum is called absorption spectrum - E = E h -E l Spectral line What A Single Spectral Line Looks Like? (a)magnified view of one spectral line (b)intensity Profile astronomy.nju.edu.cn 3

4 The Atomic Spectrum A Spectroscope Can Show a Spectrum The emission of light from an atom can be mapped in a diagram called the spectrum Hydrogen 300nm 500nm 700nm Helium Finger print of an Atom The Chemical Elements Every atom and molecule has its own distinct spectrum Spectra differ in number of lines and the spacing between the lines Each chemical element has a specific atomic configuration. The periodic table will show this for any known chemical element. Wonderwhizkid.com Temperature Scales Kelvin Scale is a thermodynamic temperature scale based on the fact that at absolute zero all atomic motion ceases. Astronomers use this scale because it is based on the motion of particle in an object Common Misconception Misconception: Temperature and heat can be used interchangeably Truth: Temperature is a measure of the average motion of the particles, whereas heat is the thermal energy moving from a hot object to a cool object 4

5 Some Everyday Examples of Kelvin Temperature What is a Black Body? Black Body Radiator. A hypothetical object that emits Electromagnetic radiation and whose spectrum is continuous with a peak in the wavelength that corresponds to the temperature of the object. Celestial Objects Produce Blackbody Radiation Spectrum of Hot Source Blackbody Radiator Two Laws of Blackbody Radiation The Stefan-Boltzmann law: The hotter an object is, the more energy it emits L=E = *T 4 where E = Energy Flux = Energy given off in the form of radiation, per unit time and per unit surface area [J/s/m 2 ] = Stefan-Boltzmann constant Two Laws of Blackbody Radiation (cont'd.) Wien s Law: The peak of the black body spectrum shifts towards shorter wavelengths when the temperature increases max 3,000,000 nm / T where T is the temperature in Kelvin 5

6 The sun =500 nm T = 3 x 10 6 /500 = 6000 K 10,000 o F Wein s Law gives the surface temperature Sun s Temperature Sun s Luminosity The sun: T= 6000 K, R=7 x 10 8 meters. What is its Luminosity? L=E = 4x 3.14 x (7 x 10 8 ) 2 x 6 x 10-8 (6000) 4 = 5 x Watts Compare with 40 watts light bulb Color and Temperature Stars appear in different colors These colors tell us about the star s temperature Reminder: Project 1 Project 1 on cross staff is due November 12. To help complete your project, I have put together some rubric to grade the project. This should help you make sure you don't loose point for incomplete work. Read the syllabus again, project 1 is 10% of your grade, so is project 2 which will be assigned after November 5th. Rubric: Project 1 will be graded on 100 point scale (50 points) Evidence to show that you have your own cross-staff and that you are not sharing one with anyone else. You can make the cross-staff with help from others or you can help them make one, but everyone should have their individual cross staff (no sharing or borrowing). (25 points) Completed data tables, including the last table to be done in planetarium on November 12th. You can work together to collect data but you cannot copy someone else data or borrow data from someone's else. Your data is unique to your cross-staff. (25 points) Completed calculations/graphs and answers to questions. You are allowed to help others or get help from others to understand how to do the calculations and plot the data, but your answers should be your own. I will check for plagiarism, and if I find evidence of identical work with someone else, you will end up with a zero in the project. For now this should help, if there is an update, I will announce it to class. Acknowledgment The slides in this lecture is for Tarleton: PHYS1411/PHYS1403 class use only Images and text material have been borrowed from various sources with appropriate citations in the slides, including PowerPoint slides from Seeds/Backman text that has been adopted for class. Cengage Learning