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Ib Physics Vocab
Section: Atomic and Nuclear Physics
| Term | Definition |
|---|---|
| Geiger-Marsden experiment | also know as Rutherford Alpha Particle Scattering or Gold Foil Experiment |
| Photon | a discrete unit or package of light energy |
| Nuclide | a particular type of nucleus with a certain number of protons and neutrons |
| Isotope | nuclei with the same number of protons (Z) but different number of neutrons (N) |
| Nucleon | a proton or neutron (NOTE: Do not say “a particle in the nucleus” since that would include quarks as well.) |
| Nucleon Number (Mass Number) (A) | number of nucleons (protons + neutrons) in nucleus |
| Proton Number (Atomic Number)(Z) | number of protons in nucleus |
| Neutron Number (N) | number of neutrons in nucleus (N = A – Z) |
| Coulomb interaction (Coulomb force, electrostatic force) | electrostatic force of repulsion between the protons in the nucleus |
| Radioactive Decay | when an unstable nucleus emits a particle (alpha, beta, gamma) (NOTE: Radioactive decay is both a random and a spontaneous process.) (NOTE: The rate of radioactive decay decreases exponentially with time.) |
| Alpha Particle (α) | helium nucleus (2 protons + 2 neutrons) |
| Beta Positive Particle (β+) | electron |
| Beta Negative Particle (β-) | positron (antielectron) |
| Gamma Radiation (γ) | high energy (high frequency) electromagnetic radiation |
| Radioactive Half life (T1/2) | a. the time taken for ½ the number of radioactive nuclei in sample to decay b. the time taken for the activity of a sample to decrease to ½ its initial value |
| Artificial (Induced) Transmutation | when a nucleus is bombarded with a nucleon, an alpha particle or another small nucleus, resulting in a nuclide with a different proton number (a different element). |
| Unified Atomic Mass Unit | 1/12th the mass of a carbon-12 nucleus |
| Mass Defect | difference between the mass of the nucleus and the sum of the masses of its individual nucleons |
| Binding Energy | energy released when a nuclide is assembled from its individual components (OR: energy required when nucleus is separated into its individual components) |
| Binding Energy per Nucleon | energy released per nucleon when a nuclide is assembled from its individual components (OR: energy required per nucleon when nucleus is separated into its individual components) |
| Nuclear Fission | a heavy nucleus splits into two smaller nuclei of roughly equal mass |
| Nuclear Fusion | two light nuclei join to form a heavier nuclei (NOTE: This is the main source of the Sun’s energy.) |
| Photoelectric Effect | the emission of electrons from a metal when electromagnetic radiation of high enough frequency falls on the surface |
| Threshold Frequency (f0) | minimum frequency of light needed to eject electrons from a metal surface |
| Work Function (Φ) | minimum energy needed to eject electrons from the surface of a metal |
| Millikan's Stopping Potential Experiment | an experiment utilizing reverse voltage raised to such a level (stopping potential Vs) that it stops all emitted photoelectrons (NOTE: This experiment is used to test the Einstein model of the explaining the photoelectric effect.) |
| de Broglie Hypothesis | All particles can behave like waves whose wavelength is given by λ = h/p where h is Planck’s constant and p is the momentum of the particle. |
| Matter Waves | All moving particles have a “matter wave” associated with them whose wavelength is the de Broglie wavelength. |
| Wave-Particle Duality | Both matter and radiation have a dual nature. They exhibit both particle and wave properties. |
| Davisson-Germer Experiment | an experiment showing that electrons are scattered off crystals of nickel and interfere with each other – also know as “electron diffraction” (NOTE: This experiment is evidence for the existence of matter waves. |
| Electron in a Box Model | a model of the atom useful for explaining the origin of atomic energy levels |
| Schrödinger Model of the Atom | This model assumes that electrons in the atom may be described by wavefunctions. The electron has an undefined position, but the square of the amplitude of the wavefunction gives the probability of finding the electron at a particular point |
| Heisenberg Uncertainty Principle | Conjugate quantities (position-momentum or time-energy) cannot be known precisely at the same time. (For example, if a particle has a uniquely defined de Broglie wavelength, then its momentum is known precisely but all knowledge of its position is lost.) |
| Bainbridge Mass Spectrometer | a device used to determine atomic masses – consists primarily of a velocity selector and a magnetic chamber |
| Radioactive Decay Law | a. The rate at which radioactive nuclei in a sample decay (the activity) is proportional to the number of radioactive nuclei present in the sample at any one time. (A = λN) b. N = N0e-λt OR A = λ N0e-λt (as an exponential function) |
| Decay Constant (λ) | a. constant of proportionality between the decay rate (activity) and the number of radioactive nuclei present b. probability of decay of a particular nuclei per unit time |
| Activity (A) | number of radioactive disintegrations (decays) per unit time |
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