Unit 13 Modern Physics

What is Light? Video (4 min)

I. Evidence for Wave Behavior of Light Double Slit experiment (diffraction) and polarization 3

II. Evidence for Particle Behavior of Light: A. Quantum Theory:   ENERGY A “particle” of light carrying _________ is known as a __________ 2. The energy of each quantum (photon) is directly proportional to the ____________ of the electromagnetic radiation   PHOTON FREQUENCY 4

II. Evidence for Particle Behavior of Light: Equation (See Ref. Tabs.) Because the energy is so small, electronvolts (eV) are used to simplify the amount 1 eV = _____________ (see ref tabs) 1. 60 x 10 -19 J 5

II. Evidence for Particle Behavior of Light: Example: The energy of a photon is 2.11 electron-volts. Determine the energy of the photon in joules. (B) Determine the frequency of the photon. (C) Determine the color of light associated with the photon. 6

II. Evidence for Particle Behavior of Light: B. Photoelectric Effect: (Elon Musk – Powerwall) Light above a specific frequency shining on certain metals emit electrons from the metal Phet simulation (alt. animation) 7

II. Evidence for Particle Behavior of Light: Whiteboard Problems: In which part of the electromagnetic spectrum does a photon have the MOST energy. (1) gamma rays (2) microwaves (3) visible light (4) ultraviolet 2. A photon of green light has a frequency of approximately 6.0 x 10 14 hertz. (A) Calculate the amount of energy (in joules) associated with this photon. (B) Convert the energy to electronvolts. (C) Calculate the wavelength of this photon. (1) Gamma rays 3.98 x 10 -19 J 2.49 eV 5 x 10 -7 m 8

III. De Broglie Wavelength Question: If waves can behave like particles, can particles behave like waves? Answer: YES!! 9

III. De Broglie Wavelength In 1924, De Broglie projected _____________ through a crystal. The resulting pattern was very similar to the pattern produced by the famous _______________ experiment   De Broglie proved that all particles can exhibit ________ properties ELECTRONS DOUBLE SLIT WAVE 10

Practice Problems: 4 ______ __________________ 1. In which part of the electromagnetic spectrum does a photon have the least energy? (1) X rays (2) violet light (3) infrared (4) radio waves 2. The energy of a photon varies inversely with its… frequency or wavelength. 3. Compared to a photon of red light, a photon of blue light has… (1) lower frequency and shorter wavelength (2) lower frequency and longer wavelength (3) higher frequency and shorter wavelength (4) higher frequency and longer wavelength 4. Sketch what a Photon Energy (y-axis) vs. Frequency (x-axis) graph would look like. 5. The energy of a photon is 6 eV. A) Determine the amount of energy in joules. B) Determine the wavelength. C) Determine the frequency. 6. Light (electromagnetic) energy is carried is discrete units called… 4 ______ __________________ A) 9.6 x 10 -19 J, B) 2.07 x 10 -7 m, C) 1.45 x 10 15 Hz photons 11

IV. Thomson's Model AKA "Plum Pudding" Atom Model (1904) Description of Model: Discovered the __________ - _____________ charges and ______________distributed evenly within the atom ELECTRON POSITIVE ELECTRONS 12

IV. Thomson's Model AKA "Plum Pudding" Atom Model (1904) Experiment performed in 13

V. Rutherford's Atomic Model (1911) 14

V. Rutherford's Atomic Model (1911) Description of Model: - Atom is made up of mostly ______________ - Positively charged __________ and ____________ orbit around it How it was discovered: - Alpha particles were projected at a thin gold foil - Some particles were ____________ due to the ___________ charged nucleus EMPTY SPACE NUCLEUS ELECTRONS DEFLECTED POSITIVELY 15

VI. Bohr's Atomic Model (1913) Energy (photon) Released Energy (photon) Absorbed animation 16

VI. Bohr's Atomic Model (1913) Description of Model: ____________ is emitted when an electron __________ from a higher energy state to a lower energy state Ground state: PHOTON MOVES WHEN AN ELECTRON IS IN THE LOWEST ENERGY STATE (n = 1) 17

VI. Bohr's Atomic Model (1913) NOTE: We say that the unbound electron has zero energy, when n = infinity. This means that lower energy levels must have less energy, therefore, the negatives are necessary. 18

VI. Bohr's Atomic Model (1913) Energy Emitted by an atom (see ref tabs) IMPORTANT RULE: when an electron falls from a higher energy level to a lower one, the atom emits a photon with energy equal to the difference between the energies of the initial and final states 19

Example: An electron in a hydrogen atom undergoes an energy level change from n = 5 to n =2 Find the energy of the emitted photon in eV. Find the energy of the emitted photon in J. Find the frequency of the emitted photon. D. Find the color of the emitted photon. 20

A ________________ photon is ___________________ Example: If an electron in a Mercury atom changes from level b to level e then… A ________________ photon is ___________________ [find energy in eV] [absorbed or emitted] 21

VI. Bohr's Atomic Model (1913) When an electron moves from a higher energy level to a lower energy level Energy is ____________ in the form of a _________ When an electron moves from a lower energy level to a higher energy level RELEASED PHOTON ABSORBED PHOTON 22

VII. Ionization Potential (Energy) Ion – atom that has a ___________ because of a ________ or _______ of __________ Ionization potential – energy required to ________________________ from an atom to form an _______ CHARGE LOSS GAIN ELECTRON(S) REMOVE AN ELECTRON ION 23

VII. Ionization Potential (Energy) Question: How much energy does a photon need to carry in order to ionize an electron in the d energy level of a Mercury atom? 24

VIII. Atomic Spectra Emission Spectra: Specific spectrum lines observed when electrons __________ from a _______ energy state to a _________ energy state FALL HIGH LOWER Animation & Emission Periodic Table 25

VIII. Atomic Spectra Absorption Spectra: Specific spectrum lines observed when atom _________ energy of specific frequency to ____________________ Spectroscopy and Absorption Spectra Video (4 min) ABSORBS RAISE e- TO HIGHER STATE 26

IX. Electron Cloud Model (Schrödinger) (1926) SPECIFIC ORBITS Electrons are not in ________________ Electrons are spread out in ______ CLOUDS 27

Practice Problems: 3.06 eV 4.89 x 10 -19 J 7.38 x10 14 Hz, violet A mercury atom makes a direct transition from energy level f to energy level b. A. Determine the energy in eV that is given off in this transition B. What is the energy in joules of the photon emitted in the transition C. Determine the frequency of the radiation corresponding to the emitted photon D. Explain what would happen if a 4.50 eV photon was incident on a mercury atom in the ground state. 3.06 eV 4.89 x 10 -19 J 7.38 x10 14 Hz, violet The energy would be absorbed, but does not move e- to next level because it does not have enough energy 28

X. The Atom Nucleons: the particles located in the nucleus are ___________ and _________ Strong Nuclear Force: An _____________________ between ___________ and ___________ that holds the ______________ together ______________ fundamental force NEUTRONS PROTONS ATTRACTIVE FORCE NEUTRONS PROTONS NUCLEUS STRONGEST 29

XI. Mass-Energy Relationship E = mc2 (1 min video) Showed that ________ and _________ are different forms of the same thing and are ________________ Equation (See Ref. Tabs.) MASS ENERGY EQUIVALENT 30

XI. Mass-Energy Relationship Example: Find the energy equivalent of 5 kg of mass in joules and eV. 31

XI. Mass-Energy Relationship Universal Mass Unit in terms of energy (see ref. tabs.) 931 MeV 1 u (Mass)= ___________ (Energy) (1 u = 1.66 x 10 - 27 kg) Example: Convert 5 u of mass to energy 32

XII. Nuclear Mass and Energy Problem: The sum of the masses of the parts of the nucleus (protons and neutrons) is slightly ____________ than the mass of the assembled nucleus This difference is called the _____________ Binding Energy: GREATER MASS DEFECT The missing _________________that holds the __________ together MASS (ENERGY) NUCLEUS 33

XII. Nuclear Mass and Energy Example: A uranium nucleus consisting of 92 protons and 146 neutrons has a mass of 238.0003 u. The mass of a proton is 1.0073 u and the mass of a neutron is 1.0087 u. A) Find the mass defect [difference between the total mass of the nucleons (neutrons and protons) and the mass of the nucleus]. B) Find the energy equivalent (Binding Energy) of the mass difference [in MeV]. 34

XII. Nuclear Mass and Energy Practice Problems: What particles found in an atom have APPROXIMATLEY the SAME mass and what are their mass [in kg]? What is the force that helps binds the nucleus together?____________ Calculate the energy equivalent of one neutron. [in J, eV, and MeV] Base your answers to questions 4 - 6 on the following information proton = 1.0073 u 1 neutron = 1.0087 u Determine the energy equivalent of the rest mass of a neutron in megaelectronvolts. (Show work) A tritium nucleus consists of one proton and two neutrons and has a total mass of 3.0170 universal mass units. Determine the difference in mass between the total mass of the nucleons and the mass of the tritium nucleus. (Show work) Determine how much energy is released when the atom is split? Neutron/proton 1.67 x 10 -27 kg Strong nuclear force 1.50 x10-10 J, 9.38 x108 eV, 938 MeV 939 MeV 0.0077 u 7.17 MeV 35

XIII. Fundamental Forces Fundamental Forces video Forces Strength Range of Force Strong (Nuclear) 1 Approx. 10 -15 m Electro-magnetic α 1/r2 (infinite) 10 -2 Weak (Nuclear) 10 - 5 < 10 -18 m Gravitational 10 – 39 α 1/r2 (infinite) (source) 36

XIV. Classification of Subatomic Particles Fundamental Forces video The Standard Model video All matter is classified as either __________ or ____________ (Hadrons interact through all four of the fundamental forces (strong, weak, electromagnetism, and gravity). Leptons do NOT experience the strong nuclear force. HADRONS LEPTONS 37

XIV. Classification of Subatomic Particles An electron is an example of a ____________   Hadrons are classified as either ____________ or ____________ Examples of baryons are __________________ or _____________________ LEPTONS BARYONS MESONS PROTONS NEUTRONS 38

XIV. Classification of Subatomic Particles Quarks (quark song) - Make up ___________________ and _________________________ baryons (3 quarks) mesons (quark and antiquark) Up, Up, Down (uud) - Proton: made of _____________________ Down, Down, Up (ddu) - Neutron: made of ____________________ 39

XIV. Classification of Subatomic Particles Antiparticles: Particles of same mass but opposite charge. Example: What is the name and charge of the antiparticle for an Up quark? Anti-quark: Anti-up ( u ) - 2/3 e _ Up (u) quark + 2/3 e IMPORTANT NOTE: All particles made from the subatomic particles of the standard model can not have a fraction of elementary charge. This means that all combinations of quarks and antiquarks must result in an overall charge of a whole number or zero (ie. -2, -1, 0, +1, +2) 40

XV. Particle Physics Example Questions  1. An anti baryon is composed of (1) three quarks (2) one quark and two anti quarks (3) three antiquarks (4) two quarks and one antiquark.    2. What is the electric charge on a pion composed of an up quark and an anti-down quark?  3. What is the electric charge on a particle having a quark composition of db?  4. A particle has a quark composition of dds. What is the charge on and the classification of the particle? (1) -1e, baryon (2) +1e, baryon (3) -1e, meson (4) +1e, meson 5. A particle has a quark composition of su. What is the charge on and the classification of the particle? (1) -1e, baryon (2) +1e, baryon (3) -1e, meson (4) +1e, meson 3 +1 e _ 1 _ 3 41

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