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##### Devil physics The baddest class on campus IB Physics

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**Tsokos Lesson 6-5quantum theory and the uncertainty**principle**IB Assessment Statements**• Topic 13.1, Quantum Physics: Atomic Spectra and Atomic Energy States 13.1.8. Outline a laboratory procedure for producing and observing atomic spectra. 13.1.9. Explain how atomic spectra provide evidence for the quantization of energy in atoms. 13.1.10. Calculate wavelengths of spectral lines from energy level differences and vice versa.**IB Assessment Statements**• Topic 13.1, Quantum Physics: Atomic Spectra and Atomic Energy States 13.1.11. Explain the origin of atomic energy levels in terms of the “electron in a box” model. 13.1.12. Outline the Schrödinger model of the hydrogen atom. 13.1.13. Outline the Heisenberg uncertainty principle with regard to position-momentum and time-energy.**Objectives**• Describe emission and absorption spectra and understand their significance for atomic structure • Explain the origin of atomic energy levels in terms of the ‘electron in a box’ model • Describe the hydrogen atom according to Schrödinger • Do calculations involving wavelengths of spectral lines and energy level differences**Objectives**• Outline the Heisenberg Uncertainty Principle in terms of position-momentum and time-energy**Atomic Spectra**• The spectrum of light emitted by a material is called the emission spectrum.**Atomic Spectra**• When hydrogen gas is heated to a high temperature, it gives off light • When it is analyzed through a spectrometer, the light is split into its component wavelengths**Atomic Spectra**• Different gases will have emission lines at different wavelengths • Wavelengths emitted are unique to each gas**Atomic SpectraMercury**• This is called the emission spectrum of the gas • By identifying the wavelengths of light emitted, we can identify the material**Atomic SpectraHelium**• A similar phenomenon occurs when we pass white light through a gas • On a spectrometer, white light would show a continuous band of all colors**Atomic SpectraArgon**• When passed through a gas, dark bands appear at the same frequencies as on the emission spectrum • This is called the absorption spectrum of the gas**By trial and error, Johann Balmer found that wavelengths in**hydrogen followed the formula, Atomic SpectraNeon • But nobody could figure out why • But it did show the frequencies were not random**Atomic Spectra**• Conservation of energy tells us that the emitted energy will be equal to the difference in atomic energy before and after the emission • Since the emitted light consists of photons of a specific wavelength, the energy will be discrete values following the formula,**Electron In A Box**• Wavelength zero at ends of the box • Since electron can’t lose energy, the wave in the box is a standing wave • Nodes at x = 0 and x = L**Electron In A Box**• The result is that electron energy is always a multiple of a discrete or quantized value • The same principle applies for electrons surrounding a nucleus**Schrödinger Theory**• Wave Function, Ψ(x,t) • Schrodinger equation for hydrogen • Separate equations for electrons in every type of atom**Schrödinger TheoryMax Born Interpretation**• | Ψ(x,t)|2 will give the probability that an electron will be near position x at time t**Schrödinger Theory**• Schrodinger’s Theory applied to the electron in a box model yields the following data for a hydrogen atom • Energy is discrete or quantized to one of the energy levels given by n = 1, 2, 3**Schrödinger Theory**• Energy levels of emitted photons correspond to energy level changes of electrons • Each time an electron drops in energy level, a photon is released with that energy**Schrödinger Theory**• Since E = hf, the photon will have a discrete frequency according to its energy • Knowing the energy level change of the electron, we can compute the frequency and vice versa**Schrödinger Theory**• Schrodinger’s Theory also predicts the probability that a transition will occur (| Ψ(x,t)|2) • Explains why some spectral lines are brighter**Heisenberg Uncertainty Principle**• Applied to position and momentum: • Basis is the wave-particle duality • Can’t clearly explain behavior based on wave theory or classical mechanics**Heisenberg Uncertainty Principle**• It is not possible to simultaneously determine the position and momentum of something with indefinite precision**Heisenberg Uncertainty Principle**• Making momentum accurate makes position inaccurate and vice versa**Heisenberg Uncertainty Principle**• Think of aiming a beam of electrons through a thin slit • Like polarization, we limit wave passage through the slit to a vertical plane • However, the wave will diffract which changes the horizontal position**Heisenberg Uncertainty Principle**• Even though vertical position is fairly certain, change in horizontal position means a change in momentum because of the change in the horizontal component of the velocity**Heisenberg Uncertainty Principle**• Applied to energy and time: • The same principle can be applied to energy versus time**Σary Review**• Can you describe emission and absorption spectra and understand their significance for atomic structure? • Can you explain the origin of atomic energy levels in terms of the ‘electron in a box’ model? • Can you describe the hydrogen atom according to Schrödinger?**Σary Review**• Can you do calculations involving wavelengths of spectral lines and energy level differences? • Can you outline the Heisenberg Uncertainty Principle in terms of position-momentum and time-energy?**IB Assessment Statements**• Topic 13.1, Quantum Physics: Atomic Spectra and Atomic Energy States 13.1.8. Outline a laboratory procedure for producing and observing atomic spectra. 13.1.9. Explain how atomic spectra provide evidence for the quantization of energy in atoms. 13.1.10. Calculate wavelengths of spectral lines from energy level differences and vice versa.**IB Assessment Statements**• Topic 13.1, Quantum Physics: Atomic Spectra and Atomic Energy States 13.1.11. Explain the origin of atomic energy levels in terms of the “electron in a box” model. 13.1.12. Outline the Schrödinger model of the hydrogen atom. 13.1.13. Outline the Heisenberg uncertainty principle with regard to position-momentum and time-energy.**Homework**#1-14