Modern Physics
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16 Terms
thermionic emission
thermionic emission is the escape of electrons from a metal when it is heated.
electrovolt
the electronvolt (ev) is the amount of energy gained or lost by an electron when it moves through a potential difference of one volt.
photoelectric emission
photoelectric emission is the escape of electrons from metals when light is shone onto the metal.
work function
the work function of a metal is the minimum energy required to remove an electron from the surface of the metal.
emission spectrum
the emission spectrum of an element includes all the frequencies emitted by atoms of the element when they are excited.
atomic number
the atomic number 𝑧 is the number of protons in the nucleus.
mass number
the mass number 𝑎 tells us the number of nucleons in the atom.
isotopes
isotopes are atoms having the same atomic number but different mass numbers.
natural radioactivity
natural radioactivity is the spontaneous disintegration (decay) of the nucleus of certain naturally occurring elements by the emission of an alpha-particle, a beta-particle, and/or gamma radiation.
activity
the activity, 𝑎, is defined as the number of decays occurring in unit time at a given instant.
law of radioactive decay
the law of radioactive decay states that the number of disintegrations per second is proportional to the number of nuclei present.
becquerel
the activity is 1 becquerel (bq) if, on average, one decay occurs per second.
decay constant
the decay constant is the fraction of the atoms, on average, that decay in unit time.
half-life
the half-life is the time taken, on average, for half the atoms of a radioactive material to decay.
nuclear fission
nuclear fission is the splitting of a single heavy nucleus into two or more medium-mass nuclei (of roughly equal masses) by neutron bombardment, releasing a large amount of energy.
nuclear fusion
nuclear fusion is the joining together of two or more light nuclei into a single heavier nucleus by causing them to collide at high speeds, releasing a large amount of energy.