| Term | Definition |
|---|---|
| atomic spectra | The characteristic pattern of discrete wavelengths of light emitted or absorbed by atoms, which quantum theory explains. |
| blackbody radiation | Electromagnetic radiation emitted by an idealized object that absorbs all incident radiation, explained by quantum theory. |
| de Broglie wavelength | The wavelength associated with a particle, calculated as λ = h/p, which increases as the particle's momentum decreases. |
| particle-like behavior | Properties of matter or energy that behave as discrete, localized objects with definite position and momentum, characteristic of particles. |
| photoelectric effect | The emission of electrons from a material when electromagnetic radiation is incident upon it. |
| photon | A discrete, quantized packet of electromagnetic energy that make up light, which is massless and electrically neutral, with energy proportional to its frequency. |
| quantized | Restricted to discrete, specific values rather than continuous values, as applied to energy and momentum in bound quantum systems. |
| quantum theory | The branch of physics that describes the behavior of matter and energy at atomic and subatomic scales, explaining phenomena that classical mechanics cannot. |
| wave-like behavior | Properties of matter or energy that exhibit characteristics of waves, such as interference and diffraction patterns. |
| Young's double-slit experiment | An experiment demonstrating wave properties of particles through the observation of interference patterns. |
| Term | Definition |
|---|---|
| atom | The smallest unit of matter that retains the properties of an element, consisting of a nucleus surrounded by electrons. |
| atomic element | A pure substance consisting of atoms with the same unique number of protons. |
| Bohr model | A historical model of atomic structure in which electrons move in circular orbits around the nucleus at specific energy levels determined by classical physics. |
| circular orbit | In the Bohr model, the path an electron follows around the nucleus, determined by the electron's charge, mass, and the electric force between the electron and nucleus. |
| de Broglie wavelength | The wavelength associated with a particle, calculated as λ = h/p, which increases as the particle's momentum decreases. |
| discrete energy states | Specific, quantized energy levels that an electron can occupy in an atom, as described by the Bohr model. |
| electric force | The force exerted on a charged object by an electric field. |
| electron | Negatively charged particles that serve as the primary charge carriers in most common electrical circuits. |
| ion | An atom with a nonzero net electric charge due to the loss or gain of electrons. |
| isotope | An atom of an element with a specific number of neutrons and protons that distinguishes it from other atoms of the same element. |
| neutron | A neutrally charged subatomic particle found in the nucleus of an atom. |
| nuclear notation | A symbolic representation showing the number of protons and neutrons in an atom's nucleus. |
| nucleus | The small, positively charged central part of an atom containing protons and neutrons. |
| proton | A positively charged subatomic particle found in the nucleus of an atom. |
| standing wave model | A model of electrons in atoms where the electron orbit's circumference must be an integer multiple of the electron's de Broglie wavelength, accounting for allowed energy states. |
| Term | Definition |
|---|---|
| absorption spectrum | The pattern of specific frequencies of light absorbed by an element when electrons transition to higher energy states. |
| atom | The smallest unit of matter that retains the properties of an element, consisting of a nucleus surrounded by electrons. |
| binding energy | The energy required to remove an electron from an atom and cause ionization. |
| electron | Negatively charged particles that serve as the primary charge carriers in most common electrical circuits. |
| emission spectrum | The pattern of specific frequencies of light emitted by an element when electrons transition to lower energy states. |
| energy level diagram | A visual representation showing the allowed energy states of an atom and transitions between them. |
| energy state | A specific energy level that an electron can occupy in an atom. |
| excited state | An energy state of an atom higher than the ground state, which an electron occupies after absorbing energy. |
| frequency | The number of complete wave cycles that pass a point per unit time. |
| ground state | The lowest energy level of an atom, where an electron requires the most energy to be removed. |
| interaction energy | The energy associated with the interaction between an electron and the nucleus in an atom. |
| ionization | The process of removing an electron from an atom, resulting in a charged ion. |
| nucleus | The small, positively charged central part of an atom containing protons and neutrons. |
| photon | A discrete, quantized packet of electromagnetic energy that make up light, which is massless and electrically neutral, with energy proportional to its frequency. |
| wavelength | The distance between consecutive points of the same phase in a wave, typically denoted by λ. |
| Term | Definition |
|---|---|
| blackbody | An idealized object that absorbs all electromagnetic radiation incident upon it and emits radiation based solely on its temperature. |
| continuous spectrum | A spectrum of electromagnetic radiation with all wavelengths present, emitted by a blackbody and dependent only on temperature. |
| electromagnetic radiation | A collective term for all electromagnetic waves across the entire spectrum. |
| intensity per unit wavelength | The amount of electromagnetic radiation energy emitted at each wavelength, used to characterize a blackbody's spectrum. |
| internal thermal energy | The total kinetic and potential energy of particles within an object due to its temperature. |
| peak wavelength | The wavelength at which a blackbody emits the maximum intensity of radiation per unit wavelength. |
| Planck's law | A fundamental law describing the spectral distribution of electromagnetic radiation emitted by a blackbody, based on the quantization of light energy. |
| power | The rate at which energy is transferred, converted, or dissipated in an electric circuit, measured in watts. |
| quantized energy | Energy that exists in discrete packets or quanta rather than continuous amounts. |
| Stefan-Boltzmann law | A law stating that the total power radiated by a blackbody is proportional to its surface area and the fourth power of its absolute temperature. |
| thermal equilibrium | A state in which an object maintains a constant temperature and emits energy at the same rate it absorbs energy. |
| Wien's law | A law stating that the peak wavelength of radiation emitted by a blackbody is inversely proportional to its absolute temperature. |
| Term | Definition |
|---|---|
| electromagnetic radiation | A collective term for all electromagnetic waves across the entire spectrum. |
| kinetic energy | The energy of motion possessed by an object due to its velocity. |
| monochromatic light | Light of a single wavelength or frequency. |
| photoelectric effect | The emission of electrons from a material when electromagnetic radiation is incident upon it. |
| photon | A discrete, quantized packet of electromagnetic energy that make up light, which is massless and electrically neutral, with energy proportional to its frequency. |
| threshold frequency | The minimum frequency of incident light required to cause electron emission from a material via the photoelectric effect. |
| work function | The minimum energy required to emit an electron from atoms in a material, represented by the symbol φ. |
| Term | Definition |
|---|---|
| Compton effect | The phenomenon in which a photon emerges from an interaction with an electron with lower energy and longer wavelength than the incoming photon. |
| Compton scattering | An interaction between a photon and a free electron in which the photon transfers energy and momentum to the electron, resulting in a photon with lower energy and longer wavelength. |
| conservation of energy | The principle that the total energy in an isolated system remains constant, with energy transforming between different forms but not being created or destroyed. |
| conservation of momentum | A principle stating that the total momentum of an isolated system remains constant in the absence of external forces. |
| energy | The capacity to do work; in Compton scattering, energy is transferred from the photon to the electron. |
| free electron | An electron that is not bound to an atom and can interact with a photon in Compton scattering. |
| frequency | The number of complete wave cycles that pass a point per unit time. |
| momentum | The product of mass and velocity; in Compton scattering, momentum is transferred from the photon to the electron. |
| photon | A discrete, quantized packet of electromagnetic energy that make up light, which is massless and electrically neutral, with energy proportional to its frequency. |
| wavelength | The distance between consecutive points of the same phase in a wave, typically denoted by λ. |
| Term | Definition |
|---|---|
| binding energy | The energy required to remove an electron from an atom and cause ionization. |
| conservation of energy | The principle that the total energy in an isolated system remains constant, with energy transforming between different forms but not being created or destroyed. |
| conservation of momentum | A principle stating that the total momentum of an isolated system remains constant in the absence of external forces. |
| decay constant | A parameter (λ) that characterizes the rate of radioactive decay and can be related to half-life through the equation λ = ln(2)/t₁/₂. |
| energy-mass equivalence | The principle that mass and energy are interchangeable, expressed by the equation E=mc². |
| exponential decay | A mathematical model describing how the number of radioactive nuclei decreases as a function of time, following the equation N = N₀e^(-λt). |
| half-life | The time it takes for half of the initial number of radioactive nuclei in a sample to spontaneously decay. |
| law of conservation of nucleon number | A principle stating that the total number of nucleons (protons and neutrons) remains constant in nuclear reactions. |
| neutron | A neutrally charged subatomic particle found in the nucleus of an atom. |
| nuclear fission | The process by which the nucleus of an atom splits into two or more smaller nuclei, often releasing energy. |
| nuclear fusion | The process by which two or more smaller nuclei combine to form a larger nucleus, often releasing energy. |
| nucleons | The subatomic particles that make up the nucleus, consisting of protons and neutrons. |
| proton | A positively charged subatomic particle found in the nucleus of an atom. |
| radioactive decay | The spontaneous transformation of a nucleus into one or more different nuclei, characterized by an exponential decrease in the number of radioactive nuclei over time. |
| radioactive nuclei | Unstable nuclei that spontaneously transform into different nuclei through radioactive decay. |
| strong force | The fundamental force that acts between nucleons at nuclear scales and is responsible for holding the nucleus together. |
| Term | Definition |
|---|---|
| alpha decay | A radioactive decay process in which a nucleus ejects an alpha particle. |
| alpha particle | A subatomic particle consisting of two neutrons and two protons, emitted during alpha decay; also called a helium nucleus. |
| antineutrino | The antimatter counterpart of a neutrino, with no electrical charge and negligible mass. |
| beta-minus decay | A radioactive decay process in which a neutron converts to a proton by emitting an electron and an antineutrino. |
| beta-plus decay | A radioactive decay process in which a proton converts to a neutron by emitting a positron and a neutrino. |
| gamma decay | A radioactive decay process in which an excited nucleus emits a photon to reach a lower energy state, typically following alpha or beta decay. |
| lepton number | The number of electrons and neutrinos in a system; conserved in all nuclear decay processes. |
| neutrino | A subatomic particle with no electrical charge and negligible mass that interacts with matter only through the weak force and gravity. |
| nucleon number | The total number of neutrons and protons in a nucleus; conserved in all nuclear decay processes. |
| positron | A subatomic particle with the same mass as an electron but with opposite electric charge; also called an antielectron. |
| radioactive decay | The spontaneous transformation of a nucleus into one or more different nuclei, characterized by an exponential decrease in the number of radioactive nuclei over time. |