UH PHYS 1302 - Exam3Review (6 pages)

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Exam3Review



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Exam3Review

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exam 3 review


Pages:
6
School:
University of Houston
Course:
Phys 1302 - Introductory to Physics II
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Exam 3 Review Chapter 30 Quantum Physics A blackbody is an object that perfectly absorbs and perfectly emits radiation The distribution of frequencies in blackbody radiation only depends on the temperature it does not depend on what the blackbody is made of Light of frequency f consists of photons that each have an energy E hf The more photons in a beam of light the higher the intensity of the light Photoelectric Effect A beam of light incident on a metal surface can cause electrons to be ejected A single photon is responsible for each electron that is ejected The minimum amount of energy necessary to eject an electron is called the work function W0 The energy of a photon must be at least as much as the work function to eject an electron This defines a minimum frequency for the incoming light to eject an electron f0 W0 h If the energy of the incident photon is greater than the work function the excess energy goes into kinetic energy of the ejected electron The maximum kinetic energy the ejected electron can have is given by Kmax hf W0 Increasing the intensity of the incident light means more photons hit the metal per second thus more electrons can be ejected Remember the momentum of a photon is given by p E c h When an X ray photon undergoes a collision with an electron initially at rest the photon is scattered changing its direction and energy Since the energy of the photon changes so does the wavelength and frequency The change in the wavelength 1 difference in the wavelength before and after the collision can be calculated given the scattering angle of the photon Energy and momentum are conserved in this interaction Light can exhibit both wave like and particle like properties Particles can also exhibit wave like properties The de Broglie wavelength of a particle is given by h p The de Broglie wavelengths of everyday objects like people and baseballs is so small that we don t notice the wave like properties of these objects The de Broglie wavelength of an electron is large enough that the wave like properties play a noticeable role in atomic systems The Heisenberg Uncertainty Principle states that there is a lower limit on the product of the uncertainties in a particle s position and momentum not the position and momentum themselves but in the uncertainties in those quantities This means the uncertainties are inversely related The more precisely the momentum is known small p the larger the uncertainty on the position large x and vice versa Chapter 31 Atomic Physics The Bohr Model of the Hydrogen Atom The electron in a hydrogen atom orbits the nucleus Only certain orbits are allowed The orbits are labeled by a single quantum number n 1 2 3 When an electron changes from one allowed orbit to another a photon is emitted or absorbed with the frequency of the photon determined by the difference in energy of the orbits E hf hc This explains the spectral lines in hydrogen The Bohr Model can be used for any atom with atomic number Z if there is only one electron orbiting the nucleus The energy of a Bohr orbit En 13 6eV Z 2 n2 Note the negative sign The ground state of hydrogren has an energy of 13 6 eV The n state has an energy of 0 eV 2 n 1 is the ground state n 2 is the first excited state n 3 is the second excited state and so on The Quantum Mechanical Model of the Hydrogen Atom The state of a hydrogren atom requires four quantum numbers n 1 2 3 0 1 2 3 n 1 m 1 2 1 0 1 2 1 ms 1 2 The Quantum Mechnical Model of a Multielectron Atom The Pauli Exclusion Principle says no two electrons can occupy the same state have the same set of quantum numbers The ground state of a multielectron atom corresponds to all of the lowest energy levels being filled with electrons The maximum number of electrons that can occupy a subshell is given by 2 2 1 The electronic configuration indicates the arrangement of the electrons The notation for each level is n letter for number of electrons in this subshell Chapter 32 Nuclear Physics and Nuclear Radiation The species of nucleus is determined by the number of protons A nucleus with the same number of protons but different number of neutrons is called an isotope E mc2 means mass is a form of energy In nuclear reactions any change in mass must be taken into account to conserve energy We can write mass in terms of MeV c2 A mass of 1 MeV c2 has an energy equivalent of 1 MeV Remember an alpha particle is a helium nucleus 42 He 3 In beta decay if the daughter nucleus has one more proton than the parent nucleus an electron is emitted If the daughter nucleus has one less proton than the parent nucleus a positron is emitted This is due to conservation of charge the charge on the right hand side must be equal to the original charge Ze A ZX A Z 1 Y e e 1 A ZX A Z 1 Y e e 2 The energy released in a nuclear interaction is the energy that s left over once the mass energy is taken into account E mc2 mf mi c2 If a substance is radioactive the amount of the substance remaining will decrease over time as will the activity decays s The half life is the amount of time it takes for the amount of the substance or the activity to be reduced to one half its original value After two half lives 1 2 1 2 1 4 remains and so Don t confuse the half life with the decay constant which has units of inverse time Nuclear binding energy is the energy it would take break the nucleus apart into the individual protons and neutrons It is given by the difference in mass of the nucleus and the sum of the individual proton and neutron masses If you are given the atomic mass you have to subtract off the mass of the electrons to get the mass of just the nucleus The rad radiation unit gives the amount of energy deposition of radiation But it doesn t say anything about the effect of radiation on tissue as different types of radiation cause different amounts of damage However the rem radiation unit takes into account the different effects of different types of radiation A radiation dose of 1 rem does the same amount of damage no matter what kind of radiation dose in rem dose in rad x RBE where RBE is different for different types of radiation Chapter 16 Temperature and Heat The size of one degree is the same for the Celsius and Kelvin scales A change in temperature of one degree Celsius corresponds to a change in temperature of one degree Kelvin If you are working a problem that only uses temperature differences 4 T you can use Celsius Otherwise …


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