Answers for Ch. 5 A + B (Part I)

1. Answers for Ch. 5 A + B (Part I) • Part A • 4 • 3 • 3 • 1 • 4 • 4 • 1 • 2 • 4 • 3 • 4 Part B 12) 3.2 m 13) 23 m/s 14) 300 m/s 15) 12.7 m/s 16) 16.56 m 17) 14.3 m 18) There was a decrease in flight time, a 45° always produces the greatest range 19) 34.6 m/s 20) Horizontal Speed Time

2. Modern Physics Regents Physics Mr. Rockensies

3. Quantum Theory What is Quantum Theory?

4. Proposed by Max Planck in 1900. • States: “atoms absorb or emit light in discrete amounts called Quanta or Photons.” • Photon – a “particle” of light carrying energy & momentum. • Energy: Ephoton = h f or Ephoton = h c • λ • Ephoton = energy of a photon λ = wavelength • h = Planck’s constant c = speed of light in a vacuum • f = frequency of light = 3.0 x 108 m/s

5. Photon – Particle Collisions (collision between photon & electron) • Photon energy and momentum decreases • Particle energy and momentum increases • Energy and momentum are conserved

6. Matter Waves • proposed by deBroglie in 1924 • moving particles have wave properties only when particles are on a subatomic scale (electrons, protons, neutrons) • λ = h • p • λ = wavelength of subatomic particle • h = Planck’s constant • p = momentum of subatomic particle • Example: What is the matter wavelength of an electron with a speed of 2.0 x 106 m/s? • λ = h • p • λ = 6.62 x 10-34 J·s • (2.0 x 106 m/s)(9.1 x 10-31 kg) • λ = 3.6 x 10-10 m

7. Models of the atom How did the structure of the atom evolve?

8. Rutherford’s Model Experiment (1911) The detecting screen was illuminated with a flash of light every time an alpha particle hit it.

9. Rutherford’s Conclusions 1 % of alpha particles deflected into hyperbolic paths 99% of alpha particles passed through foil most of the atom is empty space positive charge and mass of atom is concentrated in a small dense core called the nucleus. Rutherford’s atom

10. Bohr’s Model (1913) Bohr’s model agreed with what Rutherford had said two years previously, but added on certain distinctions • electrons move in orbits, shells, or energy levels around the nucleus and can move from one energy level to another. • Energy Level Diagrams • each atom of a particular element • has what is called an energy level • diagram • shows the energy levels or states • of an atom Bohr’s Model of the Atom

11. Energy Level Diagrams • Ground State • electron is in its lowest energy level • atom is most stable • electron has least amount of energy • Excited State • electron jumps to a higher energy level • atom is less stable • electron has more energy • Ionization Level • atom is “ionized” when electron is removed from atom • Ionization energy – energy needed to remove an electron from atom • ** Signs indicate the energy the atom lacks to become ionized when in that state

12. Results of Absorption/Emission ABSORPTIONEMISSION atoms absorb energy by absorbing energy of both colliding: electrons (electrical energy) photons (light energy) atoms release energy in the form of photons (light) Absorption/Emission Spectrum

13. How do we predict the colors an element will give off? On the reference table: Ephoton (electron) = Ei - Ef Ephoton (electron) = energy of photon absorbed or released by atom OR energy of electron absorbed by atom Ei = initial energy of electron in the atom Ef = final energy of electron in the atom • If we know the energy of the photon, we can then use E = hf to find the frequency of that photon. • If we know the frequency, then we can use our reference tables to look up the corresponding color. • We could also calculate wavelength using c = fλ

14. What color is the photon? An electron is excited to the 3rd energy level, n=3, and then drops back down to n=2. How much energy is given off by the atom when the electron falls down? What is the frequency of the photon being emitted? What is the wavelength of that photon? What is the color of that photon? Ephoton = Ei – Ef Ephoton = -1.51 eV – (-3.40 eV) Ephoton = 1.89 eV (must convert to J) Ephoton = hf 3.02x10-19 J =(6.63x10-34 J•s)f f = 4.56x1014 Hz c = fλ 3x108 m/s =(4.56x1014 Hz)λ λ = 6.58x10-7 m Color on reference table: Red 1 eV = 1.6x10-19J

15. Cloud Model States that there is no specific orbit for an electron as it moves about the nucleus. Instead, there is a region of most probable electron location called an electron cloud.

16. Atomic Spectra Emission/Bright line Spectrum

17. How do we see the emission/bright line spectrum? Spectroscope (contains a prism) colored light is passed through gas discharge tube with Xenon gas Emission Spectrum for Xenon

18. Emission Spectrum A series of bright lines of color on a black background Unique for each element (can be used to identify an element) Each line of color corresponds to an energy level change for an electron and a wavelength emitted by the material Absorption Spectrum A series of dark lines on a bright background A characteristic set of light wavelengths absorbed by a material Absorption/Emission Spectrum

20. Einstein’s Mass-Energy Relationships

21. What is Einstein’s Theory of Relativity? • A mass, m, is equivalent to an amount of energy, E • As an equation – E = mc2 • Where: E = Energy equivalent in Joules • m = mass of 1 atomic mass unit (a.m.u.) in kg • **1 a.m.u. = 1.66x10-27 kg** • c = speed of light in air/vacuum This equation eventually led to the creation of this (nuke)

22. What is the Energy Equivalent of 1 a.m.u. (Proton or Neutron)? E = mc2 E = (1.66x10-27 kg)(3.0x108 m/s)2 E = 1.49x10-10 Joules E = 9.31x108 eV = 931MeV million electron-volts 1 a.m.u. = 9.31x102 or 931 MeV **Conversion factor on Reference Table**

23. Example #1

24. Example #2

25. Example #3

26. Example #4

27. Example #5

28. Fundamental Forces What are the four fundamental forces in order from strongest to weakest?

29. Strong Force Nuclear Force which holds a nucleus of an atom together against the enormous forces of repulsion of the protons Short Ranged – range is 10-15 meters (diameter of a medium sized nucleus

30. Electromagnetic Force Manifests itself through the forces between charges and the magnetic force Can be attractive or repulsive Long Ranged – range is infinite

31. Weak Force Involved in many decays of nuclear particles Responsible for the fusion of the Sun and the conversion of neutrons to protons in the nuclei Short Ranged – range is 10-17 meters

32. Gravity A purely attractive force which acts along the line joining the centers of mass of the two masses The forces on the 2 masses are equal in size, but opposite in direction, obeying Newton’s 3rd Law Long Ranged – range is infinite

33. Classification of Matter How is all matter classified?

34. The Standard Model All Matter Hadrons (Heavy) Leptons (Light) Baryons(Very Heavy) Mesons (Medium Heavy) Made of 1 quark and 1 anti-quark Made of 3 quarks

35. There are a total of 6 quarks (flavors) -up, down, charm, strange, top, bottom There are also 6 anti-quarks There are also 6 Leptons - electron, electron-neutrino, muon, muon-neutrino, tau, tau-neutrino There are also 6 anti-Leptons

36. Bosons – The Four Fundamental Force Carriers • Strong Force gluon g • Weak Force W boson • Electric Force photon γ • Gravity Force graviton G -Never detected

37. Common Baryons • Proton p uud • Anti-proton p ūūd • Neutron n udd • Omega Ω sss

38. Common Mesons • Pion π+ ud • Anti-pion π- ūd • Kaon k- sū

39. Conservation Laws still apply • Mass/Energy - the total amount of mass and energy equivalent of mass (E=mc^2) is constant • Momentum • Charge • Quantization of Charge (quarks)