Physics Extra Glossary (6/27/01)
absolute index of refraction
A property of optical substances equal to the ratio of the speed of light in a vacuum to the speed of light in the substance.
(four words)
absolute temperature
A measure of the average kinetic energy of the molecules of a body.
(two words)
absolute zero
The theoretical lower limit of temperature designated as 0 on the Kelvin scale.
(two words)
absorption spectrum
A continuous spectrum, like that of white light, interrupted by dark lines that are produced by the absorption of certain wavelengths by a substance (often a gas) through which the light or other radiation passes.
(two words)
acceleration
The time rate of change of velocity; a vector quantity.
acceptor material
A substance used as an additive to a semiconductor in order to increase the density of holes in the semiconductor.
(two words)
alpha decay
The phenomenon of spontaneous ejection of a helium ion from an atomic nucleus.
(two words)
alpha particle
A helium nucleus-a particle consisting of two protons and two neutrons.
(two words)
alternating current
An electron flow in a circuit that changes rapidly many times per second in direction or magnitude.
(two words)
ammeter
A device designed to measure electric current when connected in series in an electric circuit; a galvanometer with a low resistance connected in parallel with the galvanometer coil.
ampere
The fundamental SI unit of current, which is equal to one coulomb per second.
amplifier
Any device that increases the amplitude of a signal without appreciably changing its wave form.
amplitude
The magnitude of the maximum displacement of a vibrating field or maximum displacement of a particle from its rest position.
angle of incidence
The angle between a ray of light and the normal to the surface at the point where the ray strikes the surface.
(three words)
angle of reflection
The angle between a ray of light that is reflected from a surface and the normal to that surface at the point where the ray is reflected.
(three words)
angle of refraction
The angle between a ray emerging from the interface of two media and the normal to that interface at the point where the ray emerges.
(three words)
anode
A terminal in an electric circuit that is connected to the positive terminal of a battery or other source of potential difference.
antinodal lines
A region of maximum displacement of a medium in which waves are interacting.
(two words)
aphelion
The point in a planet's orbit that is farthest from the sun; the point in the orbit where the planet has the smallest speed and the largest gravitational potential energy relative to the sun.
atomic mass unit
A unit of mass in particle physics defined as 1/12 the mass of a carbon-12 nucleus.
(three words)
atomic number
A number indicating the number of protons in the nucleus of an atom of a specific element.
(two words)
atomic spectrum
The characteristic frequencies of electromagnetic radiation produced by each element.
(two words)
average speed
The total distance traveled by an object divided by the time of its travel; a scalar quantity.
(two words)
back EMF
The potential difference induced in the armature of an operating motor that opposes the applied potential difference.
(two words)
Balmer series
The visible red, green, and violet spectral lines produced by electrons of hydrogen falling from a higher energy state to the lower state designated n = 2.
(two words)
baryons
In an atom, subatomic particles of the largest masses (including protons and neutrons).
base
The middle layer in a transistor.
battery
A combination of two or more electric cells.
beta decay
The process of spontaneous emission of an electron from the nucleus of an atom; alternatively, the emission of positrons during induced radioactivity.
(two words)
beta particle
An electron emitted spontaneously from a radioactive atomic nucleus.
(two words)
binding energy
The energy required to break up the nucleus of an atom into the individual protons and neutrons of which the nucleus is composed; the energy equivalent of the mass defect.
(two words)
boiling
The condition in which the liquid and gaseous phases of matter are in equilibrium, usually at atmospheric pressure.
Boyle's law
The volume of a sample of gas is inversely proportional to the pressure, provided the temperature is constant.
(two words)
breakdown voltage
A reverse potential difference that causes a large reverse current in a diode.
(two words)
breeder reactor
A nuclear reactor designed to produce more fissionable fuel than is consumed.
(two words)
bright-line spectrum
A display of bright individual lines on a plate or other surface, indicating the radiation of energy at specific frequencies by a heated gas at low pressure.
(three words)
cathode
The negative terminal of a battery or some other source of potential difference.
cathode ray tube
An evacuated glass tube in which a beam of electrons, accelerated and deflected by electric fields or magnetic fields or both, produces an image on a fluorescent screen.
(three words)
Celsius scale
The temperature scale on which the freezing point of water is 0 degrees and the boiling point of water is 100 degrees at standard pressure.
(two words)
center of curvature
The point that is equidistant from every point on the surface of a spherical mirror.
(three words)
centripetal acceleration
The acceleration of a body moving along a circular path at constant speed; a vector quantity.
(two words)
centripetal force
The force needed to keep an object moving in a circular path; a vector quantity directed toward the center of the circular path.
(two words)
chain reaction
A fission reaction producing sufficient energy and neutrons to be self-sustaining once the reaction has begun.
(two words)
Charles' law
This law states that the volume occupied by a sample of gas is directly proportional to the Kelvin temperature, provided the pressure exerted by the sample is constant.
(two words)
chromatic aberration
The inability of a single lens to refract all the different colors of light to the same focus.
(two words)
coefficient of friction
The ratio of the force needed to overcome friction to the normal force pressing two surfaces together.
(three words)
coherent
A term applied to a beam of waves, all of which possess an identical wavelength and an identical constant phase relationship.
collector
One of the two outer layers in a transistor; the layer less heavily doped.
commutator
A split ring in a DC motor, the segments of which are connected to the armature coil in such a way that the current in the coil reverses direction every half turn.
component
One of the two or more forces into which a given vector may be resolved.
concave lens
A diverging lens that causes incident parallel rays to emerge from the lens as if the rays diverged from a point.
(two words)
concave mirror
A spherical mirror whose reflecting surface curves inward from the edges to the center.
(two words)
concurrent forces
Two or more forces acting on the same body at the same time.
(two words)
conduction band
In a semiconductor, the energy band that defines the magnitudes of those electrons that can readily move and transport electric charge.
(two words)
conductor
A substance, usually a metal, in which electric charge moves easily.
conservation of mass-energy
During a change in which mass is converted into energy, the total of the mass and energy remains constant.
(four words)
conservative force
A force whose work performed on a system can be recovered without loss.
(two words)
constructive interference
The effect produced by the interaction of two waves that are in phase with each other as they pass through a medium.
(two words)
control rod
A device used to regulate the rate of a nuclear chain reaction.
(two words)
converging lens
A lens capable of refracting incident light rays so as to form an image on a screen; a lens that is thicker at the center than at the edges.
(two words)
converging mirror
A concave mirror.
(two words)
convex lens
A converging lens.
(two words)
convex mirror
A spherical mirror whose reflecting surface curves outward from the edges to the center.
(two words)
coolant
A fluid circulated through a nuclear reactor to remove heat generated by fission.
core
The part of a nuclear reactor where the fuel rods are placed and where fission occurs.
coulomb
The SI unit of electric charge equal to one ampere of current passing through a given area in one second; a derived unit.
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.
(two words)
critical angle
The angle an incident ray makes with the normal when the refracted ray is at a right angle to the normal.
(two words)
critical mass
The minimum amount of a fissionable nuclide needed to sustain a chain reaction.
(two words)
current
The rate at which electric charge is transferred in an electric circuit; a scalar quantity.
current element
A theoretical unit for testing the strength of a magnetic field, consisting of a specific length of conductor carrying a standard current.
(two words)
cycle
One of a complete sequence of repetitive events, vibrations, or oscillations that constitute a wave.
derived unit
A combination of two or more fundamental units of measure.
(two words)
destructive interference
The effect produced by the interaction of two waves out of phase with one another as they pass simultaneously through a medium.
(two words)
deuterium
An isotope of hydrogen that has one proton and one neutron in the nucleus.
diffraction
The movement of waves around corners and obstacles in their paths.
diffuse reflection
The reflection of parallel light rays incident on unpolished or irregular surfaces.
(two words)
diode
A device that conducts electric current more readily in one direction than in another.
direct current
An electric current that flows in a circuit in one direction at a steady rate.
(two words)
dispersion
The separation of light consisting of more than one wavelength into its spectrum.
dispersive medium
An optical medium that produces the effect of dispersion.
(two words)
displacement
The change of position of an object described by the vector that begins at the initial position of the object and ends at its final position.
distance
The total length of a path; a scalar quantity.
diverging lens
A lens that refracts incident light rays so that no image can be produced on a screen; a lens that is thinner at the center than at the edges.
(two words)
diverging mirror
A convex mirror.
(two words)
donor material
A substance containing impurities that increase the number of electrons available; the N-type semiconductor in a transistor.
(two words)
doping
A process of adding atoms having three or five valence electrons to a semiconducting material to increase its conductivity.
Doppler effect
An apparent change in frequency and wavelength when a wave source and observer are in relative motion with respect to each other; the effect is observed for sound and light waves.
(two words)
dynamics
The branch of physics dealing with the motion of masses as various forces are applied to them; the study of how forces acting on a object affect its motion.
efficiency
The ratio of the power from the secondary coil of a transformer to the power input to the primary coil.
elastic potential energy
The energy stored in a spring when work is done in compressing or stretching it; a scalar quantity.
(three words)
electric cell
A device for generating electricity by chemical action.
(two words)
electric circuit
The complete path taken by electrons during their passage through various interconnected wires and components.
(two words)
electric current
The flow of electric charge between two points in an electric circuit due to a potential difference between the points.
(two words)
electric field
A region in which electrical force acts on a charged particle.
(two words)
electric field intensity
The force on a unit charge at a point in an electric field; a vector quantity.
(three words)
electric motor
A current-carrying coil, which, as a result of experiencing a torque in a magnetic field, converts electrical energy into rotational mechanical energy.
(two words)
electrical ground
An arbitrary zero potential reference point, from which potential difference may be measured, very often the earth itself or a negative terminal of a battery.
(two words)
electromagnet
A coil of wire wound around a soft iron core whose magnetic field may be controlled by passing an electric current through the coil.
electromagnetic induction
The production of an electrical potential or current in a conductor due to the relative motion of the conductor in a magnetic field or a change in magnetic field relative to the conductor; the process of inducing a potential difference in a conductor that occurs when there is a change in the number of lines of magnetic flux linked by the conductor.
(two words)
electromagnetic spectrum
The range of frequencies of electromagnetic waves that encompass radio and television waves, microwaves, visible and invisible light, x-rays, gamma rays, and rays of still higher frequency.
(two words)
electromagnetic wave
A wave generated by an oscillating charge producing interacting electric and magnetic fields that propagate into space.
(two words)
electron
A subatomic particle bearing a negative electric charge and having negligible mass compared to a proton.
electron capture
The process whereby an orbital electron is absorbed by a proton in a nucleus possessing too many protons compared to the number of neutrons.
(two words)
electron cloud
The region inside an atom where the negative electrons are most likely to be found.
electron gun
A device consisting of a cathode for producing electrons by thermionic emission and a cylindrical anode for accelerating the electrons and forming them into an electron beam.
(two words)
electronvolt
A unit of energy equal to the work done moving an elementary charge through a potential difference of one volt.
electroscope
An instrument used to detect the nature of electrostatic charge on a mass.
elementary charge
The charge on the electron.
(two words)
elementary unit of charge
A charge equal to the negative charge on an electron or the positive charge on a proton.
(four words)
ellipse
A closed curve in which the sum of the distances from any point on the curve to two fixed points (the foci) inside the curve is constant; an oval-shaped curve.
EMF
The potential difference produced as a result of the conversion of other forms of energy into electrical energy.
(initials)
emission spectrum
The set of electromagnetic frequencies emitted by any source when energized.
(two words)
emitter
One of the two outer layers in a transistor; the layer that is heavily doped.
energy
The capacity to perform work; a scalar quantity.
energy band
A group of many energy levels in a semiconductor having nearly, but not exactly, the same energy.
(two words)
Energy Band Model
A theory, replacing the cloud or Electron-Sea Model of conduction, that explains the electrical behavior of semiconductors.
(three words)
energy level
One of a series of regions about the nucleus of an atom in which an electron may move; each region is associated with a specific energy value.
(two words)
entropy
A quantitative measure of a physical system's natural tendency toward increasing disorder.
equilibrant
A force that is equal in magnitude and opposite in direction to the resultant of two or more concurrent forces.
escape velocity
The velocity a body must have to escape from the earth's gravitational pull.
(two words)
excitation
The process in which an atom absorbs energy as electrons are raised to a higher energy state.
excited state
The condition of an atom whose electrons, or a nuclide whose particles, have temporarily changed their positions to positions of higher potential energy in response to the absorption of energy.
(two words)
external shielding
Material, such as high-density concrete, used to protect people from radiation at a nuclear reactor.
(two words)
extrinsic semiconductor
A semiconducting material to which impurities, such as silicon or germanium, have been added.
(two words)
ferromagnetic materials
Substances such as iron, nickel, and cobalt that are attracted by magnets.
(two words)
field
A region that is characterized by the appearance of a force on an appropriate test body, such as a unit mass in a gravitational field or a unit charge in an electric field.
field intensity
The force exerted on an appropriate test body at a particular point in a field; a vector quantity.
(two words)
field line
A line in a field that indicates the direction of the force on an appropriate test element in that field.
(two words)
first law of thermodynamics
The law of conservation of energy applied to systems involving heat energy and work.
(four words)
fission
The splitting apart of an atomic nucleus by neutron absorption with an accompanying release of energy.
fission fragments
The smaller nuclei produced by the splitting of certain heavy nuclei.
(two words)
fluid friction
The force opposing the motion of a body through a fluid (a gas or liquid); a vector quantity.
(two words)
flux density
A quantitative measure of the field intensity per unit area, expressed in terms pertinent to the nature of the field; a vector quantity.
(two words)
focal length
The distance along the principle axis between the principle focus and the center of a lens or curved mirror.
(two words)
focus
Either of the two fixed points within an ellipse used in determining the shape of the ellipse.
forbidden band
The energy band between the highest level of a valence band and the lowest level of a conduction band.
(two words)
forbidden states
In quantum theory, any energy level in an atom between the particular levels in which an electron can exist.
(two words, plural)
force
A push or pull on a mass; a vector quantity.
forward bias
A voltage applied to a P-N junction in a direction that increases both the electron and hole currents across the junction.
(two words)
free-body diagram
A representation of all the forces acting concurrently on a body.
(three words)
frequency
The number of cycles per unit time of an oscillating particle or field; a scalar quantity.
friction
A retarding force that acts parallel to surfaces in contact when a body moves or attempts to move relative to another body; a vector quantity.
fuel rods
Rods packed with nuclear fuel pellets that are placed in the core of a nuclear reactor.
(two words)
fundamental unit
An arbitrary unit in physics defined by describing a set of operations and measurements.
(two words)
fusion
The combination of two or more light nuclei accompanied by a release of energy.
galvanometer
A meter designed to measure weak electric currents when connected in series in an electric circuit.
gamma radiation
High energy photons emitted spontaneously from a radioactive atomic nucleus.
(two words)
geosynchronous orbit
The path of a satellite that always remains over the same point on the earth.
(two words)
gravitation
The mutual force of attraction between masses.
gravitational field strength
The force on a unit mass due to a gravitational field; a vector quantity.
(three words)
gravitational field strength
The force on a unit mass due to a gravitational field.
(three words)
gravitational force
The mutual force of attraction between masses.
(two words)
gravitational potential energy
The energy of a system due to the relative positions of the masses within the system.
(three words)
gravity
Gravitation, usually referring to the force that exists between the mass of the earth and the mass of a body in the vicinity of the earth.
ground state
The lowest energy state of a particle when it is neither absorbing nor radiating energy.
(two words)
half-life
The average time it takes a sample of a radioactive nuclide to disintegrate to one-half of its original mass.
heat
A manifestation of energy transfer by particle collision in a material medium; a scalar quantity.
heat of fusion
The energy required to melt one unit mass of a solid at its normal melting point.
(three words)
heat of vaporization
The energy required to change one unit mass of a liquid to a gas at its normal boiling point.
(three words)
hertz
The derived SI unit of frequency equivalent to one cycle per second.
hyperbolic
The shape of the graph that is produced when the values for two quantities that are inversely proportional to each other are plotted on Cartesian coordinates.
ideal gas
A gas for which the assumptions of the kinetic theory of gases are valid.
(two words)
image
An optical reproduction of an object by means of a lens or mirror; a display by means of an electron beam.
impulse
The product of an average applied force and the time during which it acts; a vector quantity.
incident ray
A ray of light impinging upon a surface.
(two words)
induced potential difference
A difference of potential created in a conductor due to its relative motion in a magnetic field.
(three words)
induction coil
A transformer in which a varying potential difference in the secondary coil is produced when a direct current in the primary coil is turned on and off.
(two words)
inertia
The resistance of a body to a change of motion, directly proportional to its mass.
instantaneous speed
The speed of a body at any particular instant in time; a scalar quantity.
(two words)
insulator
A substance, usually a compound or a nonmetallic element, in which electric charge flows poorly because of the absence of free electrons.
integrated circuit
A miniaturized semiconductor circuit of many components etched on a small silicon chip.
(two words)
interface
A surface that forms a boundary between two materials.
interference
The superposition of one wave on another.
interference pattern
The pattern produced by the constructive and destructive interference of waves generated in a medium by two point sources.
(two words)
internal energy
The sum of the potential and kinetic energies of a system due to the relative motion and positions of the particles of the system.
(two words)
internal shielding
A steel lining placed in the containment vessel of a nuclear reactor.
(two words)
ion
A positively or negatively charged particle produced when a neutral atom loses or gains one or more electrons.
ionization potential
The work required to remove an electron from an atom.
(two words)
isolated system
A group of bodies not being acted upon by any external force.
(two words)
isotopes
Atoms of the same element that differ from each other in the number of neutrons in their nuclei.
joule
The SI unit of energy equal to the work done by a force of one newton causing a displacement of one meter; a derived unit that is equivalent to one kilogram meter squared per second squared.
K-capture
Electron capture.
kelvin
The fundamental SI unit of temperature.
Kelvin scale
The temperature scale on which the freezing point of water at standard pressure is 273 K, the boiling point of water is 373 K, and the coldest possible temperature is 0 K.
(two words)
Kepler's first law
The orbits of all the planets are elliptical.
(three words)
Kepler's second law
A line from the sun to a planet sweeps out equal areas in equal periods of time.
(three words)
Kepler's third law
The ratio of the cube of the mean radius of a planet's orbit to the square of its period of revolution about the sun is the same for all planets in the solar system.
(three words)
kilogram
The SI unit of mass; a fundamental unit.
kilojoule
A unit of energy equal to 1,000 joules.
kilopascal
A unit of pressure equal to 1,000 pascals.
kinematics
The branch of physics concerned with the mathematics of motion.
kinetic energy
The energy of a body due to its rotational or translational motion.
(two words)
kinetic friction
The force opposing the motion of one body sliding over another; a vector quantity.
(two words)
kinetic theory of gases
The universally accepted postulate that the molecules of all matter are in a perpetual state of motion.
(four words)
laser
A device that produces a monochromatic, coherent beam of electromagnetic radiation of great energy per unit area.
law of conservation of charge
In a system that neither receives nor transmits charge, the total net charge is constant, no matter what internal changes occur.
(five words)
law of conservation of energy
In a system that neither receives nor delivers energy external to itself, the total energy of the system is constant, no matter what changes occur within the system.
(five words)
law of conservation of mass and energy
The total quantity of mass and energy in the universe remains constant.
(seven words)
law of conservation of momentum
The momentum of a system remains unchanged if no external force interacts with the system, regardless of collisions within the system.
(five words)
law of reflection
The incident ray, the refracted ray, and the normal at the point of incidence lie in the same plane, and the angle of reflection is always equal to the angle of incidence.
(three words)
lens
A transparent object with one or two curved surfaces used to direct light rays by refraction.
leptons
Subatomic particles of relatively small mass, including electrons, neutrinos, and muons.
line of force
An imaginary line drawn in a gravitational, magnetic, or electric field so that its tangent at any point is in the direction of the force on a test element in the field.
(three words)
longitudinal wave
A wave in which the oscillating particles composing the wave vibrate parallel to the direction of wave travel.
(two words)
magnet
An object that can exert a force on ferrous materials.
magnetic field
A region in which a moving charged particle will experience a force due to its motion.
(two words)
magnetic field strength
The force on a unit current element at a point in a magnetic field; a vector quantity.
(three words)
magnetic flux density
The total number of magnetic lines of flux per unit area.
(three words)
magnetic flux lines
Imaginary lines used to indicate the direction and strength of a magnetic field.
(three words, plural)
magnetic force
The force exerted on charged particles in motion in a magnetic field; a vector quantity.
(two words)
magnetic pole
A region on a magnet where the magnetic effects are most pronounced.
(two words)
majority carriers
The term describing the electrons in an N-type semiconductor or the holes in a P-type semiconductor.
(two words, plural)
mass
The property of an object defined by Newton's second law of motion; colloquially, the amount of matter composing an object.
mass defect
The difference in mass between the mass of a nucleus and the sum of the masses of the protons and neutrons that constitute the nucleus.
(two words)
mass number
The sum of all the neutrons and protons within the nucleus of an atom.
(two words)
mass spectrometer
A device used to determine the mass of ionized particles.
(two words)
mean radius
The average distance between the sun and a planet in its orbit.
(two words)
mechanics
The study of how forces affect the motions of bodies.
melting
The condition in which the solid and liquid phases of a substance are in equilibrium.
mesons
Subatomic particles whose masses are intermediate between the masses of an electron and a proton.
meter
The SI unit of length; a fundamental unit.
minority carriers
The term describing the holes in an N-type semiconductor or the electrons in a P-type semiconductor.
(two words, plural)
mirror image
The image of an object produced by regular reflection of light from a smooth, plane surface.
(two words)
moderator
A material surrounding the fuel in a nuclear reactor that slows down neutrons but has little tendency to absorb them.
momentum
The product of the mass and velocity of an object in motion; a vector quantity.
natural frequency
The particular frequency with which an elastic body will vibrate if disturbed.
(two words)
natural radioactivity
Radioactivity occurring in nature without the intervention of humans.
(two words)
negative charge
One of two types of charge; opposite to positive charge.
(two words)
net force
The single force that is equivalent to the combined effect of concurrent forces acting on a body.
(two words)
neutrino
An illusive subatomic particle of zero mass and zero charge.
neutron
A subatomic particle having no charge and a mass approximately equal to that of a proton.
newton
The derived SI unit of force; the force that imparts an acceleration of one meter per second squared to a one-kilogram mass.
nodal line
A region in a medium where the interference of waves produces a zero displacement.
(two words)
nodal point
A point of zero displacement where two waves interact.
(two words)
non-conservative force
A force, such as friction, that performs work on a system, but from which system only a lesser amount of work can be recovered.
(two words)
nondispersive medium
A medium in which waves of differing frequencies have the same speed.
(two words)
normal
A line perpendicular to a surface.
normal force
The force pressing together two surfaces that are in contact; on a horizontal surface, the normal force is equal in magnitude but opposite in direction to the weight of an object resting on the surface; a vector quantity.
(two words)
north magnetic pole
The magnetic pole from which the magnetic flux of a magnet is considered to emerge.
(three words)
nuclear force
The attractive force between particles in an atomic nucleus responsible for the stability of the nucleus; the strongest force known.
(two words)
nuclear fuel
A radioactive material whose fissionable nuclides are used to produce energy on a commercial scale.
(two words)
nuclear reactor
A device in which controlled fission reactions produce energy.
(two words)
nuclear species
A nuclide.
(two words)
nucleon
A proton or a neutron in a nucleus of an atom.
nucleus
The positively charged core of an atom made up of one or more protons and (except for one of the isotopes of hydrogen) one or more neutrons.
nuclide
An atomic nucleus specified by its atomic number, atomic mass, and energy state.
ohm
The derived SI unit of electrical resistance equivalent to one volt per ampere.
Ohm's law
At constant temperature, the ratio of the potential difference across a resistor to the current flowing in the resistor is constant.
(two words)
optical center
The center of a converging or diverging lens.
(two words)
parallel circuit
A circuit in which the ends of two or more devices are connected to the same points so as to provide two or more paths for the flow of current.
(two words)
particle accelerator
A device that uses electric and electromagnetic fields to increase the speed of atomic or nuclear particles.
(two words)
pascal
The SI unit of pressure equal to one newton per square meter; a derived unit.
perihelion
The point in a planet's orbit that is closest to the sun and at which the planet has the greatest speed and smallest gravitational potential energy.
period
The time taken for an oscillating body or wave to complete one cycle; the time required for a body to make one complete revolution in its orbit; a scalar quantity.
periodic waves
A series of regularly repeated disturbances of a field or medium.
(two words, plural)
phase
The relative position of a point on a wave with respect to another point on the same wave.
photoelectric effect
The phenomenon in which electromagnetic radiation interacts with a substance with a subsequent emission of electrons.
(two words)
photon
The basic unit of electromagnetic energy.
Planck's constant
A universal constant relating the energy of a photon to the frequency of the radiation from which it comes.
(two words)
polarization
The condition of light or radiant energy in which all vibrations are confined to a single plane perpendicular to the direction of the wave's motion.
polarized light
A beam of light in which all the wave oscillations are in one plane only.
(two words)
pole
A region on the surface of a mass where there is a great concentration of magnetic or electric lines of force.
polychromatic waves
Light having many frequencies.
(two words, plural)
positive beta decay
The emission of positrons from an atomic nucleus.
(three words)
positive charge
One of two types of charge; opposite to negative charge.
(two words)
positron
A particle whose mass is equal to the mass of the electron, and whose positive electric charge is equal in magnitude to the negative charge of the electron.
positron emission
The spontaneous ejection of a positively charged electron from the nucleus of an atom that occurs when a proton in the nucleus changes to a neutron.
(two words)
potential difference
The difference in potential energy per unit charge between two points in an electric field.
(two words)
potential energy
The stored energy of a body in terms of its condition or position with respect to other bodies; a scalar quantity.
(two words)
power
The time rate of utilization of energy; the time rate of doing work; a scalar quantity.
pressure
The force exerted on one unit of area; a scalar quantity.
primary coil
In a transformer, the wire coil connected to a source of alternating current.
(two words)
principal axis
An imaginary line passing through the center of curvature and the center of a curved mirror or lens.
(two words)
principal focus
A point to which rays parallel to the principal axis of a lens or mirror converge, or from which they diverge, after reflection or refraction.
(two words)
principal quantum numbers
The integers, beginning with one, that are assigned to successive energy levels of an atom.
(three words)
prism
A transparent optical device having two identical triangles as sides and three rectangular faces; used for dispersion or refraction of light.
protium
An isotope of hydrogen whose nucleus is composed of one proton (and no neutrons).
proton
A positively charged subatomic particle with a charge equal in magnitude to that of the electron and a mass number of 1.
pulse
An abrupt non-periodic disturbance of a field or medium.
quantum
An individual discrete packet of energy radiated and absorbed as a unit.
quantum theory
The modem theory, extensively verified, that radiant energy is emitted from and absorbed by matter in discrete packets of energy (quanta).
(two words)
quark
A particle deduced to exist, not yet isolated, but for which there is now evidence of its existence; it possesses a fractional elementary charge.
radioactive decay
The spontaneous disintegration of the nuclei of atoms causing the formation of new nuclei.
(two words)
radius of curvature
The distance from the center of curvature to the curved surface of a spherical mirror.
(two words)
ray
A straight line indicating the direction of travel of a wave.
real image
An image formed by an optical system that can be focused on a screen.
(two words)
reflected ray
The ray appearing from a surface when an incident ray strikes the interface between two media of different optical densities.
(two words)
refraction
The bending of the path of a ray when it passes obliquely from one medium to another of different optical density.
regular reflection
The reflection produced when light rays are incident upon a smooth plane surface.
(two words)
resistance
The opposition of a circuit or part of a circuit to the flow of current; the ratio of applied potential difference to current through a circuit element; a scalar quantity.
resistivity
A quantity property of a material, independent of the material's physical shape, that is closely related to its resistance; can be calculated from a sample of uniform composition by multiplying the resistance of the sample by the ratio of its area to length.
resolution of forces
The process of determining the magnitude and direction of the components of a force.
(three words)
resonance
Sympathetic vibrations in a body at its natural vibrational frequency set up by another vibrating force at the same frequency.
reverse bias
A voltage applied to a P-N junction that reduces the electron current across the junction.
(two words)
rolling friction
The force opposing the motion of one body rolling over another body; a vector quantity.
(two words)
satellite
A natural or human-made body that revolves about a larger body.
scalar
A physical quantity, such as length and mass, characterized by magnitude only.
second
The SI unit of time; a fundamental unit.
second law of thermodynamics
Heat will not flow from a cold body to a warm body unless work is done; the entropy of the universe is increasing.
(four words)
secondary coil
In a transformer, the wire coil in which an alternating potential difference is induced.
(two words)
semiconductor
A material whose resistivity lies between that of insulators and conductors.
series circuit
An electrical circuit connected so that there is only one path for electron flow.
(two words)
shunt
A low resistance in an ammeter that has been placed in parallel with a galvanometer coil.
sliding friction
A force that resists the relative motion of objects that are in contact with each other; a vector quantity.
(two words)
Snell's law
For a ray passing from one medium to another, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for all angles of incidence.
(two words)
solenoid
A coil of wire of one or more layers .wound on a solid or air core; used as a component in electrical circuits.
south magnetic pole
That pole of a magnet into which the magnetic lines of flux flow.
(three words)
specific heat
The heat energy required to raise the temperature of a unit mass of a substance one Celsius degree.
(two words)
speed
The time rate at which a body travels distance; a scalar quantity.
spherical aberration
The failure of mirrors and lenses with spherical surfaces to bring parallel light rays striking all parts of the mirror or lens to the same focus.
(two words)
spherical mirror
A mirror having a reflecting surface that is a portion of a sphere.
(two words)
spring constant
The ratio of the force required to stretch or compress a particular spring to the distance of stretch or compression.
(two words)
standard pressure
A pressure of 101.3 kilopascals.
(two words)
standing wave
A stationary wave pattern formed in a medium when two sets of waves of equal wavelength and amplitude pass through the medium in opposite directions.
(two words)
starting friction
When two bodies are in contact, the minimum force required to begin moving one body relative to the other; a vector quantity.
(two words)
static electricity
Stationary electric charges.
(two words)
static equilibrium
The condition of a body when it has a net force of zero acting on it; the condition of a body at rest or moving with a constant velocity.
(two words)
static friction
The force preventing the motion of one body relative to another when they are at rest with respect to each other; a vector quantity.
(two words)
statics
The study of the forces acting on a body when it is at rest or is moving so that its center of mass has a constant velocity.
stationary state
The energy condition of an electron in an atom in which it neither absorbs nor radiates energy.
(two words)
superposition
The process of determining the resultant wave of two or more interfering waves.
temperature
The measure of a substance's warmth or coldness with respect to a standard; a scalar quantity.
tesla
The SI unit of flux density equal to one weber per square meter and equivalent to a magnetic field strength of one newton per ampere meter; a derived unit.
test charge
A small positively charged mass used to detect an electric field.
(two words)
test mass
A hypothetical small mass used to detect a gravitational field.
(two words)
thermal neutrons
Neutrons likely to cause fission because they have kinetic energies close to those of the molecules of a substance at ordinary temperatures.
(two words, plural)
thermionic emission
The emission of electrons at high temperatures when metallic filaments or cores are heated.
(two words)
thermometer
A device that is used to make quantitative measurements of temperature.
third law of thermodynamics
The temperature of a system cannot be reduced to absolute zero by a finite number of operations.
(four words)
threshold frequency
The frequency below which electromagnetic radiation will not eject electrons from the surface of a given metal.
(two words)
torque
A force applied perpendicular to a designated line that tends to produce circular motion.
total internal reflection
The reflection of a ray in a denser medium from the surface of a less dense medium that occurs when the angle of incidence exceeds the critical angle.
(three words)
total mechanical energy
The sum of the potential and kinetic energies of a mechanical system.
(three words)
transformer
Two coils used to change the potential difference of an alternating current to a larger or smaller alternating potential difference.
transistor
A semiconductor device, used in the place of the vacuum tube, that is able to control current and to generate, shape, and amplify wave forms of a wide range of frequencies with such efficiency that it has formed the basis for the current advances in electrical technology.
transmutation
The conversion of an atomic nucleus of one element into that of another element by a loss or gain of protons.
transverse wave
A wave whose oscillating particles or oscillating field vibrates perpendicular to the direction of wave travel.
(two words)
tritium
An isotope of hydrogen whose nucleus is composed of one proton and two neutrons.
uniform circular motion
Constant speed in a circular path.
(three words)
uniform motion
Straight-line motion at constant speed.
(two words)
unit
A standard value for a quantity used for comparing other values of the same quantity.
universal law of 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.
(four words)
uranium disintegration series
The sequence of nuclides formed as uranium-238 decays by alpha and beta particle emissions to the stable nuclide lead-206.
(three words)
valence band
The band of energy that encompasses the energy magnitudes of the outermost electrons of the atoms of a solid material.
(two words)
vector
A quantity, such as velocity and force, described by both magnitude and direction; often depicted graphically by a directed line segment.
velocity
The time rate of change of displacement; a vector whose magnitude is speed and whose direction is the direction of motion.
virtual focus
The point at which rays diverging from a lens would meet if extended in straight lines back through the lens.
(two words)
virtual image
An image formed by an optical system that cannot be focused on a screen.
(two words)
visible light
The portion of the electromagnetic spectrum whose frequencies produce the sensation of color when viewed.
(two words)
volt
The derived SI unit of electric potential difference, equal to one joule per coulomb.
volt per meter
The SI unit of electric field intensity equal to a newton per coulomb; a derived unit.
(three words)
voltmeter
An electrical device used to measure the potential difference across an element when connected in parallel with it in an electric circuit; a galvanometer with a high resistance connected in series with the galvanometer coil.
watt
The derived SI unit of power, equal to one joule per second.
wave
A series of periodic oscillations of a particle or a field in time and space.
wave front
All points on a three-dimensional wave that are in phase with each other.
(two words)
wavelength
The distance between any two corresponding points on adjacent cycles of a wave that are in the same phase.
weber
The derived SI unit of magnetic flux.
weight
The gravitational force of attraction of the earth on a body, or in space the attraction of one celestial body for another; a vector quantity.
work
For a force whose magnitude and direction are constant while applied to a body, the product of the magnitude of the body's displacement during the time the force acts times the component of the force in the direction of the displacement; a scalar quantity.
work function
The minimum energy required to remove an electron from the surface of a metal.
(two words)