Vijay Shankar Sharma
Textbook physics terms. Not a BFUT reinterpretation. 371 terms. Textbook meanings only.
371 terms. Page 3 of 8.
em · intro
The complete range of electromagnetic radiation, ordered by wavelength or frequency, spanning from long-wavelength radio waves through microwaves, infrared, visible light, ultraviolet, X-rays, and finally short-wavelength gamma rays. All forms of electromagnetic radiation travel at the speed of light in a vacuum and consist of oscillating electric and magnetic fields, differing only in their wavelength and the energy carried by their photons.
em · intro
A wave consisting of oscillating electric and magnetic fields that propagate through space, including light, radio waves, and X-rays, all traveling at the speed of light in a vacuum. Unlike sound waves, electromagnetic waves require no medium and can travel through the vacuum of space. James Clerk Maxwell first predicted their existence mathematically in the 1860s by combining the laws of electricity and magnetism.
particle · intro
A subatomic particle with a negative electric charge and very little mass compared to protons and neutrons, found orbiting the nucleus in atoms and responsible for chemical bonding and electric current in conductors. Electrons are classified as leptons and, as far as experiments have shown, have no internal substructure. Their behavior is governed by quantum mechanics rather than classical physics, exhibiting both particle-like and wave-like properties.
particle · intro
Also called: eV
A unit of energy commonly used in atomic, nuclear, and particle physics, defined as the energy gained by a single electron accelerating through an electric potential difference of one volt. Because it is a very small unit, energies are often expressed in kilo-, mega-, or giga-electron-volts. The electron volt is convenient because typical atomic and subatomic energy scales come out as manageable numbers rather than extremely small numbers of joules.
particle · intermediate
A unified description of the electromagnetic force and the weak nuclear force, showing that at very high energies, such as those present shortly after the early hot phase of the universe, these two forces merge into a single electroweak force. At lower energies typical of everyday conditions, the two forces appear distinct. This unification, developed by Sheldon Glashow, Abdus Salam, and Steven Weinberg, is a core part of the Standard Model of particle physics.
em · intro
The smallest unit of electric charge that occurs freely in nature, carried by a single proton, with a value of approximately 1.602 times ten to the minus nineteen coulombs. The electron carries the same magnitude of charge but with a negative sign. All observed free electric charges are whole-number multiples of the elementary charge, a property known as charge quantization.
em · intermediate
Also called: electromotive force
A measure of the energy per unit charge supplied by a source, such as a battery or generator, that drives current around a circuit, measured in volts. Despite its name, electromotive force is not actually a force but an energy-per-charge quantity, similar to voltage, though emf specifically refers to the driving energy source rather than a potential difference across a passive component.
mechanics · intro
A fundamental physical quantity representing the capacity of a system to do work or produce change, existing in many interconvertible forms including kinetic, potential, thermal, chemical, and electromagnetic energy. Energy is measured in joules and is conserved in every known physical process, though it can change form or transfer between systems. The concept of energy unifies vastly different areas of physics under a single accounting framework.
quantum · intro
One of the specific, discrete amounts of energy that a bound quantum system, such as an electron in an atom, is allowed to have, according to quantum mechanics. Unlike classical systems, which can have any energy value, quantum systems can only occupy these fixed levels, and transitions between levels involve absorbing or emitting a photon with energy equal to the difference between the two levels. This quantization explains the sharp spectral lines seen in atomic spectra.
thermo · intermediate
A measure of the disorder, or more precisely the number of microscopic arrangements consistent with a system's macroscopic state, central to the second law of thermodynamics. In any isolated system, entropy tends to increase over time, which is why heat flows from hot to cold objects and not the reverse, and why processes like mixing are generally irreversible. Entropy provides a direction to time in physics, sometimes called the arrow of time.
mechanics · intro
A state in which a system experiences no net change over time, because opposing influences are balanced. Mechanical equilibrium occurs when the net force and net torque on an object are both zero, so it remains at rest or moves at constant velocity. Thermal equilibrium occurs when two objects in contact reach the same temperature and no further net heat flows between them.
thermo · intermediate
A result from statistical mechanics stating that, in thermal equilibrium, energy is distributed equally among all the accessible degrees of freedom of a system, with each contributing an equal average share of the total thermal energy. This theorem explains, for example, why the specific heat of a gas depends on how many ways its molecules can store energy, such as through translation, rotation, and vibration. It works well for classical systems but breaks down at low temperatures where quantum effects dominate.
mechanics · intro
The minimum speed an object needs to break free from a massive body's gravitational pull without further propulsion, ignoring atmospheric drag. It depends on the mass and radius of the body being escaped; for Earth, escape velocity is about 11.2 kilometers per second, while for the Sun it is much higher. Escape velocity is derived by setting an object's kinetic energy equal to the gravitational potential energy needed to reach an infinite distance.
relativity · intro
The boundary surrounding a black hole beyond which nothing, including light, can escape its gravitational pull. Once any object or information crosses the event horizon, it is causally disconnected from the outside universe and inevitably continues toward the central singularity. The size of the event horizon, described by the Schwarzschild radius for a non-rotating black hole, depends directly on the black hole's mass.
nuclear · intro
A pattern of change in which a quantity decreases at a rate proportional to its current value, resulting in the quantity shrinking by the same fraction over equal time intervals. Radioactive decay, the discharge of a capacitor, and the absorption of light passing through a material all follow exponential decay. It is mathematically described using the constant e and is characterized by a fixed half-life or time constant.
em · intro
The SI unit of electrical capacitance, defined as the capacitance of a capacitor that stores one coulomb of charge when a voltage of one volt is applied across it. One farad is an unusually large amount of capacitance for practical electronic components, so capacitors are typically rated in microfarads, nanofarads, or picofarads. The unit is named after English scientist Michael Faraday.
em · intermediate
A law of electromagnetism stating that the voltage induced in a closed loop of wire is proportional to the rate of change of magnetic flux through that loop. It explains how a changing magnetic field can generate electricity, forming the basis for electric generators and transformers. Combined with Lenz's law, which gives the direction of the induced current, Faraday's law is one of the four fundamental relationships summarized in Maxwell's equations.
particle · intermediate
A category of particle that follows the Pauli exclusion principle, meaning no two identical fermions can occupy the same quantum state simultaneously. All the basic building blocks of matter, including electrons, protons, neutrons, and quarks, are fermions. Fermions have half-integer values of a quantum property called spin, distinguishing them from force-carrying bosons, which have integer spin and can share quantum states freely.
em · intermediate
A strong form of magnetism found in certain materials, such as iron, cobalt, and nickel, in which the magnetic moments of neighboring atoms align spontaneously in the same direction over small regions called domains. When these domains align with each other, the material becomes strongly magnetized and can retain magnetization even after an external field is removed. Ferromagnetism is the basis for permanent magnets and most everyday magnetic materials.
particle · intermediate
A visual and mathematical shorthand, developed by physicist Richard Feynman, used to represent and calculate the interactions between subatomic particles in quantum field theory. Straight and wavy lines represent particles, and the points where lines meet represent interactions, with each diagram corresponding to a specific mathematical term in a calculation of interaction probability. Feynman diagrams greatly simplified calculations in quantum electrodynamics and remain a standard tool throughout particle physics.
optics · intro
A technology that transmits information as pulses of light through thin, flexible strands of glass or plastic, called optical fibers, relying on total internal reflection to keep the light confined within the fiber as it travels. Fiber optic cables carry far more data over longer distances with less signal loss than traditional copper wires, forming the backbone of modern internet and telecommunications infrastructure. The technology also has applications in medical imaging and sensing.
math-methods · intermediate
A physical quantity that has a value at every point in space and time, used to describe how forces act on objects without requiring direct contact between them. Familiar examples include the gravitational field surrounding a mass, the electric field surrounding a charge, and the magnetic field surrounding a magnet or current. Modern physics treats fields as fundamental, with particles arising as excitations of underlying quantum fields.
quantum · intermediate
A fundamental dimensionless physical constant, denoted by the Greek letter alpha, that characterizes the strength of the electromagnetic interaction between charged particles, with an approximate value of 1 divided by 137. Because it combines several other fundamental constants, including the elementary charge, Planck's constant, and the speed of light, into a single pure number independent of any system of units, physicists consider it one of the most important and mysterious constants in nature, and its precise numerical value has no accepted theoretical explanation.
thermo · intro
A statement of energy conservation applied to thermodynamic systems, saying that the change in a system's internal energy equals the heat added to the system minus the work done by the system on its surroundings. It formalizes the idea that energy cannot be created or destroyed, only converted between heat, work, and stored internal energy. The first law underlies the analysis of engines, refrigerators, and virtually all thermodynamic processes.
cosmology · intermediate
A mathematical description of spacetime used as the standard framework for modern cosmology, named after Alexander Friedmann, Georges Lemaitre, Howard Robertson, and Arthur Walker, which assumes the universe is homogeneous and isotropic, meaning it looks the same at every location and in every direction on sufficiently large scales. The FLRW metric, combined with Einstein's field equations, produces the Friedmann equations that describe how the universe's expansion rate evolves over time within the Lambda-CDM model.
mechanics · intermediate
The branch of physics that studies the motion of liquids and gases and the forces acting on them, governed by equations that describe conservation of mass, momentum, and energy within a flowing fluid. Fluid dynamics explains phenomena ranging from the lift generated by an airplane wing to the flow of blood through arteries and the turbulence in a flowing river. The Navier-Stokes equations are the central mathematical description used in the field.
quantum · intro
The emission of light by a substance that has absorbed light or other electromagnetic radiation of a different, usually shorter, wavelength. Electrons in the material are excited to a higher energy state by the absorbed radiation and then quickly release the excess energy as light when they fall back down, typically within nanoseconds. Fluorescence is used in lighting, fluorescent dyes for biological imaging, and security features on currency.
optics · intro
The distance between a lens or curved mirror and the point where parallel rays of light converge after passing through or reflecting from it, called the focal point. A shorter focal length bends light more strongly and produces a wider field of view, while a longer focal length produces more magnification with a narrower field of view. Focal length is a key parameter in designing cameras, telescopes, and microscopes.
mechanics · intro
A push or pull acting on an object that can cause it to accelerate, change direction, or deform, measured in newtons. According to Newton's second law, the net force on an object equals its mass multiplied by its acceleration. Forces arise from several fundamental interactions in nature, including gravity, electromagnetism, and the strong and weak nuclear forces, and everyday forces like friction and normal force emerge from these underlying interactions.
math-methods · intermediate
A mathematical technique that decomposes a signal or function of time into the frequencies that make it up, expressing a complex waveform as a combination of simple sine and cosine waves. It is used throughout physics and engineering to analyze sound, light, and other signals, and it plays a role in quantum mechanics, where it connects a particle's position and momentum representations. The transform is named after French mathematician Joseph Fourier.
mechanics · intro
A coordinate system and set of axes relative to which the position, velocity, and motion of objects are measured and described. Different observers in different frames of reference, particularly those moving relative to each other, can measure different values for quantities like velocity, though the laws of physics themselves remain the same in all inertial frames. Reference frames are especially important in special and general relativity, where measurements of time and space depend on the observer's frame.
mechanics · intro
The motion of an object under the influence of gravity alone, with no other forces such as air resistance acting on it. In free fall near Earth's surface, all objects accelerate downward at the same rate, about 9.8 meters per second squared, regardless of their mass, as first argued by Galileo. Astronauts in orbit experience apparent weightlessness because they, along with their spacecraft, are continuously in free fall around the Earth.
waves · intro
The number of complete cycles of a repeating event, such as a wave oscillation, that occur per unit of time, measured in hertz, where one hertz equals one cycle per second. Frequency is inversely related to wavelength for waves traveling at a fixed speed; higher frequency corresponds to shorter wavelength. For light, frequency determines color, and for sound, it determines pitch.
mechanics · intro
A force that resists the relative sliding or tendency to slide between two surfaces in contact, arising from microscopic roughness and molecular interactions between the surfaces. Static friction resists the start of motion between surfaces at rest relative to each other, while kinetic friction acts once sliding has begun and is generally weaker. Friction converts kinetic energy into heat and is essential for everyday actions like walking and driving, despite also causing energy losses in machines.
astro · intro
A massive, gravitationally bound system containing stars, stellar remnants, interstellar gas and dust, and dark matter, ranging from a few million to trillions of stars. Galaxies come in several broad shapes, including spiral, elliptical, and irregular, and they often cluster together into groups, clusters, and larger superclusters connected by vast cosmic filaments. The Milky Way, home to our solar system, is a large barred spiral galaxy.
em · intro
The highest-energy, shortest-wavelength form of electromagnetic radiation, produced by extremely energetic processes such as radioactive decay, nuclear reactions, and violent astrophysical events like supernovae and black hole mergers. Gamma rays carry enough energy to damage biological tissue and are blocked effectively by thick shielding such as lead or several meters of concrete. Astronomers study gamma rays from space using orbiting telescopes, since Earth's atmosphere absorbs them before they reach the ground.
relativity · intro
Albert Einstein's theory of gravity, published in 1915, which describes gravity not as a force acting between masses but as the curvature of spacetime caused by the presence of mass and energy. Objects move along the straightest possible paths, called geodesics, through this curved spacetime. General relativity successfully predicts phenomena including the bending of light by massive objects, the precession of Mercury's orbit, gravitational time dilation, and gravitational waves.
relativity · intermediate
The shortest, or straightest possible, path between two points on a curved surface or in curved spacetime. On a flat plane, geodesics are straight lines, while on a curved surface like the surface of a sphere, they are great circles. In general relativity, objects moving under gravity alone follow geodesics through curved spacetime, which is why planets orbit stars without any force actively pulling them inward in the traditional sense.
particle · intermediate
The elementary particle that mediates the strong nuclear force, binding quarks together to form protons, neutrons, and other hadrons. Unlike photons, which carry no electric charge themselves, gluons carry the color charge associated with the strong force, allowing them to interact directly with each other, which makes the mathematics of the strong force considerably more complex. There are eight distinct types of gluon in the Standard Model.
mechanics · intro
A region of space surrounding a mass in which another mass would experience a gravitational force, described as the gravitational force per unit mass at each point. Near Earth's surface, the gravitational field has a nearly constant strength of about 9.8 newtons per kilogram, directed downward. In general relativity, the gravitational field is reinterpreted as the curvature of spacetime rather than a force field in the Newtonian sense.
relativity · intermediate
The bending of light from a distant object as it passes near a massive foreground object, such as a galaxy or galaxy cluster, caused by the curvature of spacetime predicted by general relativity. This bending can magnify, distort, or even multiply the image of the background object into arcs or rings. Gravitational lensing is a key tool for astronomers to map the distribution of both visible and dark matter in the universe.
mechanics · intro
The energy an object possesses because of its position within a gravitational field, relative to some reference point, typically increasing as the object moves farther from the source of gravity. Near Earth's surface, it is often approximated as mass multiplied by gravitational acceleration multiplied by height, though the full expression accounts for how gravity weakens with distance. This energy converts into kinetic energy as an object falls.
relativity · intermediate
A ripple in the curvature of spacetime that propagates outward at the speed of light, produced by accelerating massive objects, particularly extreme events like the merger of two black holes or neutron stars. Predicted by Einstein's general relativity in 1916, gravitational waves were first directly detected in 2015 by the LIGO observatory, opening a new way of observing the universe beyond traditional electromagnetic telescopes.
mechanics · intro
The fundamental attractive force between any two objects with mass, responsible for holding planets in orbit, giving objects weight near Earth's surface, and shaping the large-scale structure of the universe. In Newtonian physics, gravity is described as a force proportional to the product of two masses and inversely proportional to the square of the distance between them. In general relativity, gravity instead arises from the curvature of spacetime caused by mass and energy.
waves · intermediate
The speed at which the overall shape, or envelope, of a wave packet made up of multiple overlapping waves travels through space, which can differ from the speed of the individual wave crests within it, known as the phase velocity. Group velocity is the speed at which energy and information are actually transmitted by a wave packet. In some unusual materials, group velocity can even exceed or become negative relative to phase velocity without violating the fundamental speed limit for information.
particle · intermediate
A composite particle made of quarks held together by the strong nuclear force, mediated by gluons. Hadrons are divided into two families: baryons, made of three quarks, such as protons and neutrons, and mesons, made of one quark and one antiquark. Because quarks cannot be isolated individually, all observed strongly interacting particles are hadrons rather than free quarks.
nuclear · intro
The time required for half of the radioactive nuclei in a sample to decay, a characteristic value for each specific radioactive isotope that remains constant regardless of the sample's size or age. After one half-life, half the original material remains; after two half-lives, one quarter remains, and so on, following exponential decay. Half-lives range from fractions of a second to billions of years, depending on the isotope.
thermo · intro
The transfer of thermal energy between systems or objects due to a temperature difference between them, flowing spontaneously from a hotter object to a cooler one until thermal equilibrium is reached. Heat is not a property that an object possesses, unlike internal energy, but rather energy in transit, measured in joules or, in older units, calories. Heat can be transferred by conduction, convection, or radiation.
thermo · intro
The amount of heat required to raise the temperature of an object or substance by one degree, which depends on both the amount of material present and the material's specific heat. A substance with a high heat capacity, such as water, absorbs a large amount of heat with only a modest temperature rise, which is why large bodies of water moderate nearby climates. Heat capacity is distinguished from specific heat, which is heat capacity per unit mass.
quantum · intermediate
Also called: uncertainty principle
A fundamental principle of quantum mechanics, formulated by Werner Heisenberg in 1927, stating that certain pairs of physical properties, such as position and momentum, cannot both be measured or known to arbitrary precision simultaneously. The more precisely one property is determined, the less precisely the other can be known, a limit set by Planck's constant rather than by imperfect measurement tools. This is a fundamental feature of quantum reality, not merely a practical limitation.