Physical Setting / Physics Regents Examinations: Glossary of Important Physics Terms

absolute index of refraction The ratio of the speed of light in a vacuum to the speed of light in a medium.
absorption spectrum A series of dark spectral lines or bands formed by the absorption of specific wavelengths of light by atoms or molecules.
acceleration The time rate of change in velocity. The SI unit is meters per second2.
accuracy The agreement of a measured value with an accepted standard.
alpha particle A helium nucleus; a particle consisting of two protons and two neutrons.
alternating current An electric current that varies in magnitude and alternates in direction.
ammeter A device used to measure electric current. It is constructed by placing a low-resistance shunt across the coil of a galvanometer.
ampere (A) The SI unit of electric current, equivalent to the unit coulomb per second.
amplitude The maximum displacement in periodic phenomena such as wave motion, pendulum motion, and spring oscillation.
angle of incidence The angle made by the incident wave with the surface of a medium; the angle made by the incident ray with the normal to the surface of the medium.
angle of reflection The angle made by the reflected wave with the surface of a medium; the angle made by the reflected ray with the normal to the surface of the medium.
angle of refraction The angle made by the refracted wave with the surface of a medium; the angle made by the refracted ray with the normal to the surface of the medium.
anode The positive terminal of a DC source of potential difference.
antimatter One or more atoms composed entirely of antiparticles.
antinode The point or locus of points on an interference pattern (such as a standing wave or double slit pattern) that results in maximum constructive interference.
antiparticle The counterpart of a subatomic particle. An antiparticle has the same mass as its companion particle, but its electric charge is opposite in sign.
atomic number The number of protons in the nucleus of an atom. The atomic number defines the element.
Balmer series The visible-ultraviolet line spectrum of atomic hydrogen. It is the result of electrons falling from higher levels to the n = 2 state.
baryon A “heavy” particle, such as a proton or a neutron.Baryons are composed of three quarks. For example, a neutron is composed of an up quark and two down quarks (udd).
battery A combination of two or more electric cells.
beta (–) particle An electron formed in the nucleus by the disintegration of a neutron.
beta (+) particle A positron, the antiparticle of the electron, formed in the nucleus by the disintegration of a proton.
binding energy The energy equivalent of the mass defect of a nucleus.
cathode The negative terminal of a DC source of potential difference.
cathode ray tube A device for visualizing an electron beam. It consists of an evacuated tube with a source of electrons at one end and a fluorescent screen at the other end. The electron beam is controlled by electric and magnetic fields.
Celsius scale (°C) The temperature scale that fixes the (atmospheric) freezing point of water at 0° and the boiling point of water at 100°.
centripetal acceleration The acceleration that is directed along the radius and toward the center of a curved path in which an object is moving.
centripetal force The force that causes centripetal acceleration. It is responsible for changing an object’s direction, not its speed.
chromatic aberration A lens defect in which different colors of light are focused at different points.
circuit A closed loop formed by a source of potential difference connected to one or more resistances.
coefficient of friction The ratio of the force of friction on an object to the normal force on it.
coherent light A series of light waves that have a fixed phase relationship; the type of light produced by a laser. Lasers produce beams of monochromatic coherent light.
component One of the two or more vectors into which a given vector may be resolved.
concurrent forces Two or more forces acting at the same point.
conductor A material that allows electrons to flow through it freely. Metals such as copper and silver are conductors.
constructive interference The combination of two in-phase wave disturbances to produce a single wave disturbance whose amplitude is the sum of the amplitudes of the individual disturbances.
converging lens A lens that focuses its transmitted light to a point. Generally, convex lenses are converging lenses.
convex lens A lens that is thicker in the middle than at the edges.
coulomb (C) The SI unit of electric charge, approximately equal to 6.25 × 1018 elementary charges.
Coulomb’s law The electrostatic force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between the charges.
critical angle The angle of incidence for which the corresponding angle of refraction is 90°.
cycle One complete repetition of the pattern in any periodic phenomenon.
de Broglie wavelength The wavelength of a matter wave.
destructive interference The combination of two out-of-phase wave disturbances to produce a single wave disturbance whose amplitude is the difference of the amplitudes of the individual disturbances.
diffraction The bending of a wave around a barrier.
diffuse reflection The reflection of parallel light rays by irregular surfaces.
direct current An electric current that flows in one direction only.
dispersion The separation of polychromatic light into its individual colors.
displacement A change of position in a specific direction.
Doppler effect An apparent change in frequency that results when a wave source and an observer are in relative motion with respect to each other.
elastic potential energy The energy stored in a spring when it is compressed or stretched.
electric current The time rate of flow of charged particles. The SI unit of electric current is the ampere (A).
electric field The region of space around a charged object that affects other charges.
electric field intensity The ratio of the force that an electric field exerts on a charge to the magnitude of the charge.
electric motor A device that converts electrical energy into mechanical energy.
electric potential The total work done by an electric field in bringing 1 coulomb of positive charge from infinity to a specific point. The potential is a positive number if the charge is repelled by the field and a negative number if the charge is attracted by the field. At infinity, the potential is taken to be zero. Electric potential is measured in volts.
electromagnetic force The fundamental force that governs the attraction or repulsion among charged particles, whether at rest or in motion.
electromagnetic induction The process by which the magnetic field and the mechanical energy are used to generate a potential difference.
electromagnetic radiation The propagation of electromagnetic waves in space.
electromagnetic spectrum The entire range of electromagnetic waves from the lowest to the highest frequencies.
electromagnetic wave A periodic wave, consisting of mutually perpendicular electric and magnetic fields, that is radiated away from the vicinity of an accelerating charge.
electromotive force The potential difference produced as a result of the conversion of other forms of energy into electrical energy.
electron A fundamental, negatively charged, subatomic particle; a lepton.
electron-volt (eV) A unit of energy equal to the work needed to move an elementary charge across a potential difference of 1 volt.
electroscope A device used to detect the presence of electric charges.
elementary charge The magnitude of charge present on a proton or an electron. An elementary charge is approximately equal to 1.6 × 10–19 coulomb.
emission spectrum A series of bright spectral lines or bands formed by the emission of certain wavelengths of light by excited atoms falling to lower energy states.
energy A quantity related to work.
equilibrant A single balancing force that maintains the static equilibrium of an object.
equivalent resistance A single resistance that can be substituted for a group of resistances in series or in parallel.
excited state A condition in which the energy of an atom is greater than its lowest energy state.
ferromagnetic Referring to a material, such as iron, that has the ability to strengthen greatly the magnetic field of a current-carrying coil.
field lines A series of lines used to represent the magnitude and direction of a field.
fission The process of splitting a heavy nucleus, such as uranium-235, into lighter fragments. Fission is accompanied by the release of large quantities of energy.
force A push or a pull on an object. If the force is unbalanced, an acceleration will result.
frame of reference A coordinate grid and a set of synchronized clocks that can be used to determine the position and time of an event.
free fall A motion in the Earth’s gravitational field without regard to air resistance.
frequency The number of repetitions produced per unit time by periodic phenomena.
friction The force present as the result of contact between two surfaces. The direction of a frictional force is opposite to the direction of motion.
fundamental forces The four forces in nature responsible for all interactions among matter.(See also electromagnetic force, gravitational force, strong force, weak force.)
fusion (1) The process of uniting lighter nuclei, such as deuterium, into a heavier nucleus. Fusion is accompanied by the release of large quantities of energy. (2) In the study of heat and thermodynamics, a synonym for melting.
galvanometer A device, consisting of a coil-shaped wire placed between the opposite poles of a permanent magnet, that is used to detect small amounts of electric current.
gamma radiation Very high energy photons of electromagnetic radiation. Gamma photons have the highest frequencies in the electromagnetic spectrum.
geiger counter A device that detects charged nuclear particles.
generator A device that uses a magnetic field and mechanical energy to induce a source of electromotive force.
gravitational field The region of space around a mass that affects other masses.
gravitational field intensity The ratio of the force that a gravitational field exerts on a mass to the magnitude of the mass, numerically equal to the acceleration due to gravity.
gravitational force The fundamental universal attraction between masses.
gravitational potential energy The energy that an object acquires as a result of the work done in moving the object against a gravitational field.
ground An extremely large source or reservoir of electrons, which can supply or accept electrons as the need arises.
ground state The lowest energy state of an atom.
hadron Any particle that interacts through the strong force.Hadrons are classified as baryons or as mesons.
heat energy The energy that is transferred from warmer objects to cooler ones because of a temperature difference between them.
hertz (Hz) The SI unit of frequency, equivalent to the unit second–1.
image An optical reproduction of an object.
impulse The product of the net force acting on an object and the time during which the force acts. The impulse delivered to an object is equal to its change in momentum. The direction of the impulse is the direction of the force. The SI unit of impulse is the newton • second, which is equivalent to the kilogram • meter per second.
incident ray A ray of a wave impinging on a surface.
incident wave A wave impinging on a surface.
induced current An electric current that is the result of an induced electromotive force.
induced emf A potential difference created when a magnetic field is interrupted over a time period.
induction (1) A method of charging a neutral object by using a charged object and a ground. The induced charge is always opposite to the charge on the charged object. (2) See induced current and induced emf.
inertia The property of matter that resists changes in motion. Mass is the quantitative measure of inertia.
instantaneous velocity The ratio of displacement to time at any given instant; the slope of a line tangent to a displacement-time graph at any given point.
insulator A material that is a very poor conductor because it has few conduction electrons. Wood and glass are examples of insulators.
interference pattern Regions of constructive and destructive interference that are present in a medium as a result of the combination of two or more waves.
internal energy The total kinetic and potential energy associated with the atoms and molecules of an object.
joule (J) The SI unit of work and energy, equivalent to the unit newton • meter.
kilogram (kg) The SI unit of mass; a fundamental unit.
kinetic energy The energy that an object possesses because of its motion.
laser An acronym for light amplification by the stimulated emission of radiation. A laser is a device that emits extremely intense, monochromatic, coherent light.
lepton Any particle that participates in the weak force:electron, muon, tau, and their neutrinos.
longitudinal wave A wave in which the disturbance is parallel to the direction of the wave’s motion. Sound waves are longitudinal.
magnet Any material that aligns itself, when free to do so, in an approximate north-south direction. Magnets exert forces on one another and on charged particles in motion.
magnetic field The region of space around a magnet or charge in motion that exerts a force on magnets or other moving charges.
magnification The ratio of image size to object size.
mass (1) The measure of an object’s ability to obey Newton’s second law of motion. (2) The measure of an object’s ability to obey Newton’s law of universal gravitation. The SI unit of mass is the kilogram.
mass defect The mass lost by a nucleus when it is assembled from its nucleons. (See also binding energy.)
mass number The sum of the number of protons and neutrons in a nucleus; the number of nucleons the nucleus contains.
matter waves According to quantum theory, the waves associated with moving particles.
medium A material through which a disturbance, such as a wave, travels.
momentum The product of mass and velocity. The direction of an object’s momentum is the direction of its velocity. The SI unit of momentum is the kilogram • meter per second.
natural frequency A specific frequency with which an elastic body may vibrate if disturbed.
net force The unbalanced force present on an object; the accelerating force.
neutrino A lepton with no charge and questionable mass. It and its antiparticle are products of beta-decay reactions.
Newton (N) The SI unit of force, equivalent to the unit kilogram • meter per second2.
Newton’s first law of motion Objects remain in a state of uniform motion unless acted upon by an unbalanced force.
Newton’s law of universal gravitation Any two bodies in the universe are attracted to each other with a force that is directly proportional to their masses and inversely proportional to the square of the distance between them.
Newton’s second law of motion The unbalanced force on an object is equal to the product of its mass and acceleration.
Newton’s third law of motion If object A exerts a force on object B, then object B exerts an equal and opposite force on object A.
node The point or locus of points on an interference pattern, such as a standing wave or double-slit pattern, that results in total destructive interference.
normal A line perpendicular to a surface.
normal force The force that keeps two surfaces in contact. If an object is on a horizontal surface, the normal force on the object is equal to its weight.
nucleon A proton or a neutron.
nucleus The dense, positively charged core of an atom.
ohm (Ω) The SI unit of electrical resistance, equivalent to the unit volt per ampere.
Ohm’s law A relationship in which the ratio of the potential difference across certain conductors to the current in them is constant at constant temperature.
parallel circuit An electric circuit with more than one current path.
particle accelerator A device used to accelerate charged nuclear particles.
period The time for one complete repetition of a periodic phenomenon. The SI unit of period is the second.
periodic wave A regularly repeating series of waves.
phase (1) A form in which matter can exist, including liquid, solid, gas, and plasma. (2) In wave motion, the points on the wave that have specific time and space relationships.
photoelectric effect A phenomenon in which light causes electrons to be ejected from certain materials.
photon The fundamental particle of electromagnetic radiation.
Planck’s constant A universal constant (h) relating the energy of a photon to its frequency; its approximate value is 6.62 × 10–34 joule • second.
point charge A charge with negligible physical dimensions.
polarization A process that produces transverse waves that vibrate in only one plane. Polarization is limited to transverse waves: light can be polarized; sound cannot.
polychromatic Referring to light waves of different colors (frequencies).
potential difference The ratio of the work required to move a test charge between two points in an electric field to the magnitude of the test charge. The unit of potential difference is the volt.
potential energy The energy that a system has because of its relative position or condition.
power The time rate at which work is done or energy is expended. The SI unit of power is the watt, which is equivalent to the unit joule per second.
precision The limit of the ability of a measuring device to reproduce a measurement.
pressure The force on a surface per unit area. The SI unit of pressure is the pascal (Pa).
proton A positively charged subatomic particle with a charge equal in magnitude to that of the electron; a baryon.
pulse A nonperiodic disturbance in a medium.
quantum A discrete quantity of energy.
quarks The particles of which protons, neutrons, baryons, and mesons are composed. Quarks carry a charge of either one-third or two-thirds of an elementary charge and come in six “flavors”: top, bottom, up, down, charm, and strange. Each quark has a companion antiquark.
radioactive decay A spontaneous change in the nucleus of an atom.
radioactivity Changes in the nucleus of an atom that produce the emission of subatomic particles or photons.
ray A straight line indicating the direction of travel of a wave.
real image An image created by the actual convergence of light waves. Real images from single mirrors and single lenses are inverted and can be projected on a screen.
refraction The change in the direction of a wave when it passes obliquely from one medium to another in which it moves at different speed.
regular reflection The reflection of parallel light rays incident on a smooth plane surface.
resistance The opposition of a material to the flow of electrons through it; the ratio of potential difference to current.
resistivity A quantity that allows the resistance of substances to be compared. Numerically, it is the resistance of a 1-meter conductor with a cross-sectional area of 1 square meter. The SI unit of resistivity is the ohm•meter.
resistor A device that supplies resistance to a circuit.
resolution The process of determining the magnitude and direction of the components of a vector.
resonance The spontaneous vibration of an object at a frequency equal to that of the wave that initiates the resonant vibration.
resultant A vector sum.
satellite A body that revolves around a larger body as a result of a gravitational force.
scalar quantity A quantity, such as mass or work, that has magnitude but not direction.
series circuit A circuit with only one current path.
significant digits The digits that are part of any measurement.
solenoid A coil of wire wound as a helix. When a current is passed through the solenoid, it becomes an electromagnet.
speed The time rate of change of distance; the magnitude of velocity. The SI unit of speed is the meter per second.
spring constant The ratio of the force required to stretch or compress a spring to the magnitude of the stretch or compression.
standard model A model of matter and the fundamental interactions that govern it.
standing wave A wave pattern created by the continual interference of an incident wave with its reflected counterpart. The standing wave does not travel, but oscillates about an equilibrium position.
static equilibrium The condition of a body when a net force of zero is acting on it.
superconductor A material with no electrical resistance.
strong force The strongest of the four fundamental forces. It mediates interactions among certain nuclear particles.
temperature The “hotness” of an object, measured with respect to a chosen standard.
torque A force, applied perpendicularly to a designated line, that tends to produce rotational motion.
total internal reflection The reflection of a wave inside a relatively dense medium produced when the angle of the wave with the boundary exceeds the critical angle.
total mechanical energy The sum of the potential and kinetic energies of a mechanical system.
transverse wave A wave in which the disturbance is perpendicular to the direction of the wave’s motion. Light waves are transverse.
uniform In the study of motion, a term that is equivalent to constant.
vector A representation of a vector quantity; an arrow in which the length represents the magnitude of the quantity and the arrowhead points in the direction of its orientation.
vector quantity A quantity, such as force or velocity, that has both magnitude and direction.
velocity The time rate of change of displacement.
virtual image An image formed by projecting diverging light behind a mirror or a lens.
volt (V) The SI unit of potential difference, equivalent to the unit joule per coulomb.
voltage Another term for potential difference.
voltmeter A device used to measure potential difference and constructed by placing a large resistor in series with the coil of a galvanometer.
watt (W) The SI unit of power, equivalent to the unit joule per second.
wave A series of periodic oscillations of a particle or a field both in time and in space.
wave front All points on a wave that are in phase with each other.
wavelength The length of one complete wave cycle.
weak force The fundamental force that arises in certain types of radioactive decay.
weight The gravitational force present on an object.
work The product of the force on an object and its displacement. The SI unit of work is the joule.