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Modern Physics

Modern Physics. Answer Me!!!. How much energy does a photon have if the light beam has a wavelength of 720 nm?. Thomson Model. This is known as the plum pudding model:. Rutherford’s Experiment. Gold foil was bombarded with alpha particles (helium nuclei).

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Modern Physics

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  1. Modern Physics

  2. Answer Me!!! • How much energy does a photon have if the light beam has a wavelength of 720 nm?

  3. Thomson Model • This is known as the plum pudding model:

  4. Rutherford’s Experiment • Gold foil was bombarded with alpha particles (helium nuclei). • Most particles went straight through, showing an atom is primarily empty space. • Some alpha particles were deflected along a hyperbolic path when they struck the positive nucleus of the gold.

  5. Rutherford’s Model • Most of the mass of the atom is in the central nucleus which is positive. • Most of the atom is empty space. • Electrons go around the nucleus.

  6. Bohr Model

  7. Electron Cloud Model • Electrons don’t follow specific paths in energy levels (orbital paths). • Instead, energy levels represent locations with high probability of finding an electron.

  8. Energy Levels • In order to move to a higher energy level, a specific amount of energy must be absorbed. • If an electron moves to a lower energy level that energy will be released as a photon.

  9. Energy Level - Hydrogen • Each of the values represents the amount of energy necessary to bind an electron at that energy level. • To find the energy in a specific transition, calculate the difference between the two energy levels. • Ephoton = Ei -Ef

  10. Practice Problem 1 • An electron in a hydrogen atom drops from n=3 to n=2 energy level. • What is the energy of the emitted photon in joules? • Calculate the frequency of the emitted radiation. • What color light is this?

  11. Practice Problem 2 • If an electron is excited to the n=3 energy state, how many different frequencies of radiation can be emitted as the electron returns to the ground state?

  12. Practice Problem 3 • An electron in a mercury atom drops from energy level i to the ground state by emitting a single photon. What is the energy of this photon?

  13. Spectral Lines • When an electron absorbs energy from a photon, a dark band (absorption line) can be seen through a spectroscope. • When an electron emits energy, a bright colored band (emission line) can be seen through a spectroscope. • Each atom has a specific group of spectral lines that can be used to identify its composition.

  14. Answer Me!!! Where does all of our energy come from?

  15. The Atom • An atom is the smallest part of an element that has the characteristics of the element. • Atoms are composed of • Protons • Neutrons • Electrons

  16. The Nucleus • Protons and neutrons are held in the nucleus of an atom. • Protons and neutrons are held together in the nucleus by a strong force. • The strong force is a short range attractive force between nucleons.

  17. Nuclear Fission

  18. Mass-Energy Equivalence • When an atom or particle is decomposed, some of its mass will be converted into energy according to Einstein’s theory: E = mc2 E is Energy created (in Joules) m is mass lost (in kg) c is the speed of light in a vacuum (in m/s)

  19. All of the Energy in the Universe? • The original source of all the universe’s energy is the conversion of mass to energy.

  20. Practice Problem 4 • What is the energy equivalent of a mass of 0.026 kg?

  21. Practice Problem 5 • What is the energy equivalent of the rest mass of a proton? • How much energy would be created when a proton and an antiproton annihilate each other?

  22. Answer Me!!! • What is matter made from?

  23. Standard Sub-Atomic Particles • All matter is classified into two categories: hadrons and leptons. • Protons and neutrons are hadrons. • Electrons, positrons, neutrinos are leptons.

  24. Quarks • There are six distinct types of quarks: up, down, charm, strange, top, bottom. • Each quark possesses a fractional charge (+2/3 or -1/3 elementary charge) • A Proton is made from three quarks: uud • A Neutron is made from three quarks: udd

  25. Anti-quarks • Six distinct anti-quarks exist and they are related to the six quarks. • If a quark (ex. u) has a charge of +2/3, the anti-quark (ex. ū) has a charge of -2/3.

  26. Hadrons • Hadrons are matter that is composed of quarks. • Hadrons are divided into two groups – baryons and mesons. • Protons, Neutrons and Pions are examples of Hadrons.

  27. Baryons • Baryons are heavier particles made of three quarks. • Protons (uud) and neutrons (udd) are both baryons.

  28. Meson • Mesons are lighter than baryons, but heavier than leptons. • Mesons are composed of one quark and one anti-quark. • Mesons can have a charge of 0e, +1e or -1e. • Example Pion

  29. Leptons • Leptons are particles that have very little mass. • Leptons are bound with the weak nuclear force. • Examples of leptons are: electrons, muons and tau particles. Also, each of these has a counterpart neutrino that is a lepton.

  30. Practice Problem 6 • Protons and neutrons are examples of?

  31. Practice Problem 7 • Which combination of quarks would produce a neutral baryon? • uud • udd • ūdd • ūūd

  32. Practice Problem 8 • During beta decay, a neutron decays into a proton by the introduction of an electron antineutrino. During this process, there is a conversion of • An u quark to a d quark • A d quark to a meson • A baryon to another baryon • A lepton to another baryon

  33. Answer Me!!! • Which of the following is a stable baryon? • dsc • ssu • ud • tbs

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