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happyphysics.com Physics Lecture Resources Prof. Mineesh Gulati Head-Physics Wing Happy Model Hr. Sec. School, Udhampur, J&K Website: happyphysics.com

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Ch 38 Photons, Electrons, and Atoms © 2005 Pearson Education

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38.1 Emission and Absorption of Light Line spectra Line spectra Photoelectric Effect Photoelectric Effect X-Rays X-Rays Photons and Energy Levels Photons and Energy Levels © 2005 Pearson Education

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38.1 Emission and Absorption of Light © 2005 Pearson Education Continuous spectrum Line spectrum

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38.2 the Photoelectric Effect © 2005 Pearson Education

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photoelectric effect momentum of a photon © 2005 Pearson Education energy of a photon

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38.3 Atomic Line Spectra and Energy Levels energy of emitted photon © 2005 Pearson Education

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energy levels of the hydrogen atom © 2005 Pearson Education The hydrogen spectrum

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© 2005 Pearson Education

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38.4 The Nuclear Atom © 2005 Pearson Education Rutherford scattering experiment

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© 2005 Pearson Education Thomson’s model Rutherford’s model

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© 2005 Pearson Education Computer simulation of scattering

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38.5 The Bohr Model © 2005 Pearson Education Classical physics prediction Electron should continuously radiate electromagnetic waves and spiral into the nucleus

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© 2005 Pearson Education Bohr model Proton is assumed to be stationary; the electron revolves in a circle of radius r n with speed v n

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quantization of angular momentum orbit radii in the Bohr model orbital speeds in the Bohr model © 2005 Pearson Education

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Reduced mass m r m1 m2

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© 2005 Pearson Education Energy level of different atoms

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38.6 The Laser © 2005 Pearson Education

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Population inversion

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38.7 X-Ray Production and Scattering bremsstrahlung limits © 2005 Pearson Education

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Compton scattering © 2005 Pearson Education

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38.8 Continuous Spectra Black body © 2005 Pearson Education

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Stefan-Boltzmann law for a blackbody Wien displacement law Planck radiation law © 2005 Pearson Education

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38.9 Wave-Particle Duality © 2005 Pearson Education

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The energy in an electromagnetic wave is carried in units called photons. The energy E of one photon is proportional to the wave frequency f and inversely proportional to the wavelength λ, and is proportional to a universal quantity h called Planck’s constant. The momentum of a photon has magnitude E/c. (See Example 38.1)

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In the photoelectric effect, a surface can eject an electron by absorbing a photon whose energy hf is greater than or equal to the work function φ of the material. The stopping potential V 0 is the voltage required to stop a current of ejected electrons from reaching an anode. (See Examples 38.2 and 38.3) © 2005 Pearson Education

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When an atom makes a transition from an energy level E i to a lower level E f, the energy of the emitted photon is equal to E i -E f. The energy levels of the hydrogen atom are given by Eq. (38.9), where R is the Rydberg constant. All of the observed spectral series of hydrogen can be understood in terms of these levels. (See Example 38.4)

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© 2005 Pearson Education The Rutherford scattering experiments show that at the center of an atom is a dense nucleus, much smaller than the overall size of the atom but containing all of the positive charge and most of the mass. (See Example 38.5)

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© 2005 Pearson Education In the Bohr model of the hydrogen atom, the permitted values of angular momentum are integral multiples of h/2π. The integer multiplier n is called the principal quantum number for the level. The orbital radii are proportional to n 2 and the orbital speeds are proportional to 1/n. (See Example 38.6)

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© 2005 Pearson Education The laser operates on the principle of stimulated emission, by which many photons with identical wavelength and phase are emitted. Laser operation requires a non-equilibrium condition called a population inversion, in which more atoms are in a higher-energy state than are in a lower-energy state.

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© 2005 Pearson Education X rays can be produced by electron impact on a target. If electrons are accelerated through a potential increase V ac, the maximum frequency and minimum wavelength that they can produce is given by Eq. (38.22). (See Example 38.7)

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© 2005 Pearson Education Compton scattering is scattering of x-ray photons by electrons. For free electrons (mass m), the wavelengths of incident and scattered photons are related to the photon scattering angle φ by Eq. (38.23). (See Example 38.8)

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The total radiated intensity (average power radiated per area) from a blackbody surface is proportional to the fourth power of the absolute temperature T. The quantity is called the Stefan- Boltzmann constant. The wavelength λ m at which a blackbody radiates most strongly is inversely proportional to T. The Planck radiation law gives the spectral emittance I(λ) (intensity per wavelength interval in blackbody radiation. © 2005 Pearson Education

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Electromagnetic radiation behaves as both waves and particles. A comprehensive theory must include both of these aspects of its behavior.

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END Visit: happyphysics.com For Physics Resources

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