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Modern Physics
Definitions
| Term | Definition |
|---|---|
| Electron | Indivisible quantity of charge that orbits the nucleus of an atom |
| Thermionic Emission | Emission of electrons from the surface of a hot metal |
| Work Function | Minimum energy needed to remove the loosest electrons from the surface of a metal |
| X-rays | Electromagnetic radiation of extremely high frequency and short wavelength |
| Photoelectric Effect | Emission of electrons from the surface of a metal due to electromagnetic radiation of a suitable frequency hitting the metal |
| Photon | Bundle of light energy |
| Threshold Frequency | Minimum frequency needed to cause photoelectric emission |
| Protons | Positively charged nucleons, with the same size charge as the electron |
| Neutrons | Electrically neutral nucleons, with slightly larger mass than protons |
| Atomic Number | Number of protons in the nucleus of an atom |
| Mass Number | Number of protons plus neutrons in the nucleus of an atom |
| Isotopes | Atoms of the same atomic number but different mass number |
| Radioactivity | Spontaneous emission of radiation due to the natural disintegration of an unstable nucleus |
| Ionisation | The charging of a neutral atom or molecule when it loses or gains one or more electrons |
| Penetration | Distance that radiation travels through a medium |
| Radioisotope | An unstable isotope of an element that decays spontaneously emitting radiation |
| Alpha Emission | The emission of a helium nucleus from a large atom |
| Beta Emission | The emission of an electron when a neutron decays into a proton |
| Gamma Emission | The emission of high energy photons from an unstable nucleus |
| Radioactive Activity | The rate of emissions from a radioactive source |
| Half-life | Time taken for half of the nuclei in a given sample of radioactive isotope to decay |
| Nuclear Fission | The splitting of a large nucleus into two smaller nuclei of roughly equal mass, with emission of neutrons and release of energy |
| Nuclear Fusion | The combining of two small nuclei to form a single larger nucleus, with the release of energy |
| Chain Reactions | Where at least one neutron is released during each fission reaction |
| Critical Mass | Minimum amount of fissile material needed in order for chain reactions to occur |
| Radiation | Emission of particles of matter or photons of energy |
| Background Radiation | Radiation that comes from environmental sources including the Earth's crust, the atmosphere, cosmic rays and radioisotopes |
Created by:
conordesmond
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