MCAT Physics: Atomic and Nuclear Phenomena – Flashcards
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- When light of a sufficiently high frequency is incident on a metal in a vacuum, the metal ions emit electrons - liberated electrons produce a current
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Photoelectric Effect
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- The minimum frequency of light that causes ejection of electrons (ft) - photoelectric effect is an all or nothing response
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Threshold Frequency
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- light quanta in a light beam
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Photon
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E=hf - energy of each photon is proportional to light h= 6.626 x 10^-34 - energy of a photon increases with increasing frequency
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Energy of each photon
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where W is the work function of the metal in question - energy can be anywhere from 0 to Kmax
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Maximum kinetic energy of the ejected electron
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- The minimum energy required to emit an electron - W=h ft (ft = threshold frequency) - activation energy in a sense
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Work Function
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- when an electron falls from a higher energy level to a lower energy level, a photon of light is emitted with an energy equal to the energy difference between the two orbitals
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Absorption and Emission
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- looks at the absorption of light in the visible and ultraviolet range
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UV- Vis Spectroscopy
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- if you excite a fluorescent substance with UV radiation it will begin to glow with visible light
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Fluorescence
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- mass of the nucleus is NOT the sum of the masses of all the protons and neutrons inside of it - The actual mass is slightly smaller due to matter being converted to energy E=mc^2 - because c is squared, a small amount of mass will yield a huge amount of energy
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Mass Defect
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- When protons and neutrons come together to form the nucleus they are attracted to each other by this force - binding energy allows the nucleons to bind together
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Strong Nuclear Force
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- much less strong than strong nuclear force
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Weak Nuclear Force
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- small nuclei combine to form a larger nucleus
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Fusion
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- large nucleus splits into smaller nuclei - chain reaction - powers most commercial power plants
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Fission
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- naturally occurring spontaneous decay accompanied by the emission of specific particles Know these types of problems 1) the integer arithmetic of particle and isotope species 2) Radioactive half life problems 3) The use of exponential decay curves and decay constants
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Radioactive Decay
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- the sum of the atomic numbers must be the same on both sides of the equation and the sum of the mass numbers must be the same on both sides as well
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Isotope Decay Arithmetic and Nucleon Conversion
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- Emission of an alpha particle - alpha particle consists of two protons, two neutrons and zero electrons - atomic number is 2 less and mass number is 4 less
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Alpha Decay
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- emission of a beta particle which is an electron - emitted when a neutron decays into a proton, a beta particle and an antineutrino
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Beta Decay
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- neutron converted to a proton and a beta - particle - atomic number is one higher and mass number does not change
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Beta - Decay
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- a proton is converted into a neutron and a beta + particle - the atomic number will be one lower and the mass number will not change
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Beta + Decay
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- The emission of gamma rays which are high energy photons - carry now charge and simply lower the energy of the parent nucleus without changing the mass or atomic number
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Gamma Decay
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- capture an inner electron that combines with a proton to form a neutron - atomic number is one less but the mass number stays the same
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Electron Capture
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- the time it takes for half of the sample to decay
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Half Life
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- the rate at which nuclei decay is proportional to the number that remain - gamma is decay constant
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Exponential Decay
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- n(o) is the number of undecayed nuclei at t=0
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Exponential Decay
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ln 2=0.693
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Decay constant and half life
