Pluto via New Horizons Credit NASA JHUIAPL SwRI Infrared Spectra show water ice Pure water ice only Credit NASA JHUIAPL SwRI Water Ice Nitrogen Ice Methane Ice CO Ice Course Announcements Quiz 2 graded Last Names starting with A M in front of class Last Names starting with N Z in back of class Exam 1 will take place Wednesday 28 Sept Will cover Chapters 1 4 Will release study materials throughout the week Mastering Astronomy Exam 1 Study Guide now available Study sessions next Monday and Tuesday evenings combined with A151 A151 Primary Monday Night at 5 30 PM Physics 304 A152 Primary Tuesday Night at 5 30 PM Physics 304 Assignments Reading Assignments Chapter 5 Sections 5 1 5 2 and 5 4 Read by Friday 23 Sept Parallel Lectures No new parallel lectures Mastering Astronomy Chapter 4 Homework Due Monday 26 Sept at 11 59 PM EDT Quiz 2 Results Estimated Difficulty Moderate on the hard end Mean 7 1 Median 7 5 Standard Deviation 1 98 Most missed questions Red Light versus Green Light Which is faster Recognizing Newton s 2nd Law F ma or a F m The acceleration an object experiences is related to the force exerted on the object and the mass of the object Kepler s 3rd Law P2 in years a3 in AU Wein s Law The peak wavelength is inversely proportional to the temperature of an object 1 3 as hot lower temp therefore longer peak wavelength Given that the comparison object peaks at 4 m this means that the 1 3 as hot object will peak at 4 m 3 12 m Brief recap of last time The important bits to understand how light interacts with matter the field of spectroscopy Light comes in discrete packets of energy quanta which is carried by an elementary particle called a photon Energy of a photon is dependent on the wavelength That is a photon of a specific wavelength has a very exact amount of energy In an atom the electrons orbit the nucleus at very specific distances and cannot be in between these very specific distances Where the electron can be is called an orbital The electron needs to have the exact energy of that orbital to be in that orbital No other energy will do The lowest energy orbital is where electrons like to be This is orbital is called the ground state An electron can jump between orbitals only if it absorbs the exact amount of energy required to go into a higher further from the nucleus orbital or if it gives up emits the exact amount of energy to fall into a lower closer to the nucleus and the ground state Brief recap of last time The important bits to understand how light interacts with matter the field of spectroscopy The energy required for the electron s jumps and falls between different orbitals comes in the form of light packets photons If a photon has the exact right amount of energy the right wavelength that corresponds to the energy need for an electron to jump to a higher excited state then that atom will absorb that wavelength color of light Electrons will naturally make their way back to their lowest energy state toward the ground state For them to fall from one orbital to another they must shed the extra energy they have the lower state is lower energy If that electron gains energy from a photon and jumps to an excited state we say the atom has absorbed the photon If the electron falls to a lower energy orbital lower excited state or ground state it releases the energy as a photon with energy equal to the energy difference between the two orbitals Here we say the atom has emitted a photon Spectrum of Hydrogen Spectral Series Lyman Series Transitions starting or ending at the Ground State n 1 Ultraviolet Lines L 121 6 nm Balmer Series Transitions starting or ending at the 1st Excited State n 2 Visible Lines H 656 3 nm Spec tral Hydr Seri ogenes Ener gy Diagr am Balmer Series Visible Light Photons Lyman Series Ultraviolet UV Photons Spectrum of Hydrogen A spectrum of an element gives us a view of the energy structure of that element s electron energy levels H H Hydrogen Beta H Hydrogen Alpha H The Balmer Series Visible Light Emission Absorption Example Hydrogen Lines Question The Balmer Series line Hydrogen Alpha will be seen as an absorption line when the electron in the hydrogen atom makes which electronic transition A 1st Excited State to Ground State n 2 1 B Ground State to 1st Excited State n 1 2 C 2nd Excited State to Ground State n 3 1 D Ground State to 2nd Excited State n 1 3 E 2nd Excited State to 1st Excited State n 3 2 F 1st Excited State to 2nd Excited State n 2 3 Example Hydrogen Lines Question The Balmer Series line Hydrogen Alpha will be seen as an absorption line when the electron in the hydrogen atom makes which electronic transition A 1st Excited State to Ground State n 2 1 B Ground State to 1st Excited State n 1 2 Emission Absorption C 2nd Excited State to Ground State n 3 1 D Ground State to 2nd Excited State n 1 3 Emission Absorption E 2nd Excited State to 1st Excited State n 3 2 F 1st Excited State to 2nd Excited State n 2 3 Emission Absorption Kirchhoff s Laws Explained Hydrogen Gas Cloud Understanding Kirchhoff s Laws How continuous emission and absorption spectra relate Continuous spectral source the bulb emits all wavelengths of light Now imagine that continuous spectrum interacts with a cooler gas cloud full of atoms Understanding Kirchhoff s Laws Exciting the electrons to higher energies Certain energies of light wavelengths are absorbed by the atoms in the gas Occurs at the specific energies of light wavelengths that correspond to atomic electron energy levels This excites the electrons of the atoms in the gas cloud Understanding Kirchhoff s Laws Absorption Spectrum Viewing the continuous source through the cooler gas cloud If we view the gas cloud where the continuous spectral source is behind it i e continuous spectrum shining through the gas cloud we observe an Absorption Spectrum where the absorption lines indicate the chemical composition of the gas cloud Understanding Kirchhoff s Laws Emission Spectrum Viewing the gas cloud from a different angle If we view the excited gas cloud from a different angle we see an Emission Spectrum caused by the fall of the excited electrons back towards the Ground State The emission lines also indicate chemical composition of the gas Atoms heavier than Hydrogen More protons more electrons more complicated energy structure more complicated spectral lines Helium Carbon More protons and electrons means different electrical structure of atom Different electron orbital energy levels More electrons means more
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