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Mini Physics Dictionary

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Physics Dictionary

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The Letter A:

Absolute zero:  lowest possible temperature at which gas would have a zero volume.
Absorption spectrum:  spectrum of electromagnetic radiation absorbed by matter when radiation of all frequencies is passed through it.
Acceleration:  change in velocity divided by time interval over which it occurred.
Accuracy:  closeness of a measurement to the standard value of that quantity.
Achromatic lens:  lens for which all light colors have the same focal length.
Action-reaction forces:  pair of forces involved in an interaction that are equal in magnitude and opposition in direction.
Activity:  number of decays per second of a radioactive substance.
Adhesion:  force of attraction between two unlike materials.
Air resistance:  force of air on objects moving through it.
Alpha decay:  process in which a nucleus emits an alpha particle.
Alpha particle:  positively- charged particles consisting of two protons and two neutrons emitted by radioactive materials.
Ammeter:  device to measure electrical current.
Amorphous solid:  solids that have no long- range order; no crystal structure.
Ampere:  unit of electric current; one ampere is the flow of one coulomb of charge per second.
Amplitude:  in any periodic motion, the maximum displacement from equilibrium.
Angle of incidence:  angle between direction of motion of waves and a line perpendicular to surface the waves are striking.
Angle of reflection:  angle between direction of motion of waves and a line perpendicular to surface the waves are reflected from.
Angle of refraction:  angle between direction of motion of waves and a line perpendicular to surface the waves have been refracted from.
Angular momentum:  quantity of rotational motion. For a rotating object, product of moment of inertia and angular velocity.
Annihilation:  process in which a particle and its antiparticle are converted into energy.
Antenna:  device used to receive or transmit electromagnetic waves.
Antineutrino: subatomic particle with no charge or mass emitted in beta decay.
Antinode: point of maximum displacement of two superimposed waves.
Archimedes’ principle:  object immersed in a fluid has an upward force equal to the weight of the fluid displaced by the object.
Artificial radioactivity:  radioactive isotope not found in nature.
atomic mass unit:  unit of mass equal to 1/12 the atomic mass of carbon- 12 nucleus.
Atomic number:  number of protons in the nucleus of the atom.
Average acceleration:  acceleration measured over a finite time interval
Average velocity:  velocity measured over a finite time interval.

The Letter B:

Back-EMF: potential difference a cross a conductor caused by change in magnetic flux.
Band theory:  theory explaining electrical conduction in solids.
Baryon:  subatomic particle composed of three quarks.  Interacts with the strong nuclear force.
Battery: device that converts chemical to electrical energy consisting of two dissimilar conductors and an electrolyte.
Beat : slow oscillation in amplitude of a complex wave
Bernoulli’s principle:  when a fixed quantity of fluid flows, the pressure is decreased when the flow velocity increases.
Beta decay:  radioactive decay process in which an electron or positron and neutrino is emitted from a nucleus.
Beta particle:  high speed electron emitted by a radioactive nucleus in beta decay.
Binding energy:  negative of the amount of energy needed to separate a nucleus into individual nucleons.
Boiling point:  temperature at which a substance, under normal atmospheric pressure, changes from a liquid to a vapor state.
Breeder reactor:  nuclear reactor that converts nonfissionable nuclei to fissionable nuclei while producing energy.
Bubble chamber:  instrument containing superheated liquid in which the path of ionizing particles is made visible as trails of tiny bubbles.
Buoyant force:  upward force on an object immersed in fluid.

The Letter C:

Calorimeter:  device that isolates objects to measure temperature changes do to heat flow.
Candela:  unit of luminous intensity.
Capacitance:  ratio of charge stored per increase in potential difference.
Capacitor:  electrical device used to store charge and energy in the electrical field.
Capillary action:  rise of liquid in narrow tube due to surface tension.
Carnot efficiency:  ideal efficiency of heat engine or refrigerator working between two constant temperatures.
Centripetal force:  force that causes centripetal acceleration.
Chain reaction:  nuclear reaction in which neutrons are produced that can cause further reactions.
Charged :  object that has an unbalance of positive and negative electrical charges.
Charging by conduction:  process of charging by touching neutral object to a charged object.
Charging by induction:  process of charging by bringing neutral object near charged object, then removing part of resulting separated charge.
Chromatic aberration:  variation in focal length of lens with wavelength of light.
Circular motion:  motion with constant radius of curvature caused by acceleration being perpendicular to velocity.
Clock reading:  time between event and a reference time, usually zero.
Closed, isolated system:  collection of objects such that neither matter nor energy can enter or leave the collection.
Closed-pipe resonator:  cylindrical tube with one end closed and a sound source at other end.
Coefficient of friction:  ratio of frictional force and the normal force between two forces.
Coefficient of linear expansion:  change in length divided by original length and by temperature change.
Coefficient of volume expansion:  change in volume divided by original volume and by temperature change.
Coherent waves:  waves in which all are in step; are in phase.
Cohesive force:  attractive force between similar substances.
Complementary color:  two colors that, when added , produce white light.  Two pigments, that when combined, produce black.
Compound machine:  machine consisting of two or more simple machines.
Compton effect:  interaction of photons, usually X rays, with electrons in matter resulting in increased wavelength of X rays and kinetic energy of electrons.
Concave lens:  lens thinner in center than edges; a diverging lens.
Concave mirror:  converging mirror, one with center of curvature on reflecting side of mirror.
Conduction band:  energies of charge carries in a solid such that the carries are free to move.
Conductor:  materials through which charged particles move readily; or heat flow readily.
Conserved  properties:  property that is the same before and after an interaction.
Consonance: two or more sounds that, when heard together, sound pleasant.
Constant acceleration:  acceleration that does not change in time.
Constant velocity:  velocity that does not change in time.
Constructive interference:  superposition of waves resulting in a combined wave  with amplitude larger than the component waves.
Convection:  heat transfer by means of motion of fluid.
Conventional current:  motion of positive electrical current.
Converging lens:  lens that causes light rays to converge; usually a convex lens.
Convex lens: lens that is thicker in the center than at edges.
Convex mirror:  diverging mirror.  Center of curvature is on side opposite reflecting side of mirror.
Cosine:  the ratio of the adjacent side to the hypotenuse.
Coulomb:  unit of electrical charge.  Charge caused by flow of one ampere for one second.
Crest of wave:  high point of wave motion.
Critical angle:  minimum angle of incidence that produces total internal reflection.
Crystal lattice:  structure of solid consisting of regular arrangment of atoms.

The Letter D:

De Broglie wavelength:  length of de Broglie wave of particle; Planck’s constant divided by momentum of particle.
Decibel:  unit of sound level.
Dependent variable:  variable that responds to change in manipulated variable.
Derived units: unit of quantity that consists of combination of fundamental units.
Destructive interference:  superposition of waves resulting in a combined wave with zero amplitude.
Diffraction:  bending of waves around object in their path.
Diffraction grating:  material containing many parallel lines very closely spaced that produces a light spectrum by interference.
Diffuse reflection: reflection of light into many directions by rough object.
Dimensional analysis:  checking a derived equation by making sure dimensions are the same on both sides.
Diode:  electrical device permitting only one way current flow.
Dispersion of light:  variation with wavelength of speed of light through matter resulting in separation of light into spectrum.
Displacement:  change in position. A vector quantity.
Dissonance:  two or more sounds that, when together, sound unpleasant.
Distance:  separation between two points.  A scalar quantity.
Diverging lens:  lens that causes light rays to spread apart or diverge; usually a concave lens.
Dopants:  small quantities of material added to semiconductor to increase electrical conduction.
Doppler shift:  change in wavelength due to relative motion of source and detector.
Dynamics:  study of motion of particles acted on by forces.

The Letter E:

Effective current:  DC current that would produce the same heating effects.
Effective voltage:  DC potential difference that would produce the same heating effects.
Efficiency:  ratio of output work to input work.
Effort force:  force extended on a machine.
Elastic collision:  interaction between two objects in which the total energy is the same before and after the interaction.
Elasticity:  ability of object to original shape after deforming forces are removed.
Electrical charge pump:  device, often a battery or generator, that increase potential of electrical charge.
Electrical circuit:  continuous path through which electrical charges can flow.
Electrical current:  flow of charged particles.
Electrical field:  property of space around a charged object that causes forces on other charged objects.
Electric field lines:  lines representing the direction of electric field.
Electric field strength:  ratio of force exerted by field on a tiny test charge to that change.
Electric generator:  device converting mechanical energy into electrical energy.
Electric potential:  ratio of electric potential energy to charge.
Electric potential difference:  difference in electric potential between two points.
Electric potential energy:  energy of a charged body in an electrical field.
Electromagnet:  device that uses an electric current to produce a concentrated magnetic field.
Electromagnetic force:  one of fundamental forces due to electric charges, both static and moving.
Electromagnetic induction:  production of electric field or current due to change in magnetic flux.
Electromagnetic radiation:  energy carried by electromagnetic waves throughout space.
Electromagnetic waves:  wave consisting of oscillating electric and magnetic fields that move at speed of light through space.
Electromotive force:  potential difference produced by electromagnetic induction.
Electron:  subatomic particle of small mass and negative charge found in every atom.
Electron cloud:  region of high probability of finding an electron around an atom.
Electron diffraction:  effects on electrons due to wave-like interference of electrons with matter.
Electron gas model:  description of current flow through conductors.
Electroscope:  device to detect electric charges.
Electrostatics:  study of properties and results of electric charges at rest.
Electroweak force:  unification of electromagnetic and weak forces.
Elementary charge:  magnitude of the charge of an electron. 1.602 *10^  -19
Emission spectrum:  spectrum produced by radiation from excited atoms.
Energy:  non-material property capable of causing changes in matter.
Energy levels:  amounts of energy an electron in an atom may have.
Entropy:  measure of disorder in a system; ratio of heat added to temperature.
Equilibrant force:  force needed to bring an object into transitional equilibrium.
Equilibrium:  condition in which net force is equal to zero.  Condition in which net torque on object is zero.
Equivalent resistance:  single resistance that could replace several resistors.
Evaporation:  change from liquid to vapor state.
Excited state:  energy level of atom higher than ground state.
External forces:  forces exerted from outside a system.
Extrinsic semiconductor:  semiconductor in which conduction is primarily the result of added impurities.

The Letter F:

Factor-label method:  dimensional analysis.
Farad:  unit of capacitance.  One coulomb per volt.
Ferromagnetic materials:  materials in which large internal magnetic fields are generated by cooperative action of electrons.
First harmonic:  in music, the fundamental frequency.
First law of thermodynamics:  change in internal or thermal energy is equal to heat added and work done on system.  Same as law of conservation of energy.
Fluid:  material that flows, i.e. liquids, gases, and plasmas.
Focal length:  distance from the focal point to the center of a lens or vertex of a mirror.
Focal point:  location at which rays parallel to the optical axis of an ideal mirror or lens converge to a point.
Forbidden gap:  energy values that electrons in a semiconductor or insulator may not have.
Force:  agent that results in accelerating or deforming an object.
Frame of reference: coordinate system used to define motion.
Fraunhofer lines:  absorption lines in the sun’s spectrum due to gases in the solar atmosphere.
Frequency:  number of occurrences per unit time.
Friction:  force opposing relative motion of two objects are in contact.
Fundamental particles:  those particles( i.e. quarks and leptons) of which all materials are composed.
Fundamental tone:  lowest frequency sound produced by a musical instrument.
Fundamental units:  set of units on which a measurement system is based( i.e. meter, second, kilogram, ampere, candela).
Fuse:  metal safety device in an electric circuit that melts to stop current flow when current is too large.
Fusion:  combination of two nuclei into one with release of energy.

The Letter G:

Galvanometer:  device used to measure very small currents.
Gamma decay:  process by which a nucleus emits a gamma ray.
Gamma particle:  high energy photon emitted by a radioactive nucleus.
Gas:  state of matter that expands to fill container.
Geiger-Mueller tube:  device used to detect radiation using its ability to ionize matter.
General theory of relativity:  explanation of gravity and accelerated motion invented by Einstein.
Gluon:  carrier of strong nuclear force.
Grand unified theories:  theories being developed that unify the stronger and electroweak forces into one force.
Gravitational field:  distortion of space due to the presence of mass.
Gravitational force:  attraction between two objects due to their mass.
Gravitational mass:  ratio of gravitational force to object’s acceleration.
Gravitational potential energy:  change of energy of object when moved in a gravitational field.
Graviton:  particle that carries the gravitational force.  Not yet observed.
Ground state:  lowest energy level of an electron in an atom.
Grounding:  process of connecting a charged object to Earth to remove object’s unbalanced charge.

The Letter H:

Half-life:  length of time for half of a sample of radioactive material to decay.
Harmonics:  frequencies produced by musical instrument that are multiples of fundamental tone.
Heat:  quantity of energy transferred from one object to another because of a difference in temperature.
Heat engine:  device that converts thermal energy to mechanical energy.
Heat of fusion:  quantity of energy needed to change a unit mass of a substance from solid to liquid state at the melting point.
Heat of vaporization:  quantity of energy needed to change a unit mass of a substance from liquid to gaseous state at the boiling point.
Heavy water:  deuterium oxide used mainly in CANDU nuclear reactors.
Heisenberg uncertainty principle:  the more accurately one determines the position of a particle, the less accurately the momentum can be known, and vice versa.
Hertz:  unit of frequency equal to one event or cycle per second.
Hole:  absence of an electron in a semiconductor.
Hooke’s law:  deformation of an object is proportional to force causing it.
Huygens’ wavelets:  model of spreading of waves in which each point on wavefront is source of circular or spherical waves.
Hydraulic system:  machines using fluids to transmit energy.
Hyperbola:  mathematical curve that describes an inverse relationship between two variables.
Hypotenuse:  side opposite the right angle in a triangle.

The Letter I:

Ideal mechanical advantage:  in simple machine, the ratio of effort distance to resistance distance.
Illuminance:  rate at which electromagnetic wave energy falls on a surface.
Illuminated object:  object on which light falls.
Image:  reproduction of object formed with lenses or mirrors.
Impulse:  product of force and time interval over which it acts.
Impulse-momentum theorem:  impulse given to an object is equal to its change in momentum.
Incandescent body:  object that emits light because of its high temperature.
Incident wave:  wave that strikes a boundary where it is either reflected or refracted.
Incoherent light:  light consisting of waves that are not in step.
Independent variable:  variable that is manipulated or changed in an experiment.
Index of refraction:  ratio of the speed of light in vacuum to its speed in a material.
Inelastic collision:  collision in which some of the kinetic energy is changed into another form.
Inertia:  tendency of object not to change its motion.
Inertial mass:  ratio of net force exerted on object to its acceleration.
Initial velocity:  velocity of object at time t=0.
Instantaneous acceleration:  acceleration at a specific time; slope of tangent to velocity- time graph.
Instantaneous position:  position of an object at specific time.
Instantaneous velocity:  slope of the tangent to position- time graph.
Insulator:  material through which the flow of electrical charge carriers or heat is greatly reduced.
Interference fringes:  pattern of dark and light bands from interference of light waves.
Interference of waves:  displacements of two or more waves, producing either large or smaller waves.
Internal forces:  forces between objects within a system.
Intrinsic semiconductor:  semiconductor in which conduction is by charges due to host material, not impurities.
Inverse relationship:  mathematical relationship between two variables, x and y, summarized by the equation xy=k, where k is a constant.
Ionizing radiation:  particles or waves that can remove electrons from atoms, molecules, or atoms in a solid.
Isolated system:  a collection of objects not acted upon by external forces into which energy neither enters nor leaves.
Isotope:  atomic nuclei having same number of protons but different numbers of neutrons.

The Letter J:

Joule:  SI unit of energy equal to one Newton-meter.
Joule heating:  increase in temperature of electrical conductor due to conversion of electrical to thermal energy.

The Letter K:

Kelvin temperature scale:  scale with 0 K= absolute zero and 273.16 K = triple point of water.
Kepler’s laws:  three laws of motion of bodies attracted together by the gravitational force.
Kilogram:  SI unit of mass.
Kilowatt hour:  amount of energy equal to 3.6 * 10^  6 J.  Usually used in electrical measurement.
Kinematics:  study of motion of objects without regard to the causes of this motion.
Kinetic energy:  energy of object due to its motion.
Kinetic-molecular energy:  description of matter as being made up of extremely small particles in constant motion.

The Letter L:

Laser: devise that produces coherent light by stimulated emission of radiation.
Laser- induced fusion:  proposed method of creating nuclear fusion by using heating caused by intense laser beams to squeeze matter together.
Law of conservation of energy:  in a closed, isolated system, the total momentum is constant.
Law of reflection:  angle of incidence of a wave is equal to the angle of reflection.
Law of universal gravitation:  gravitational force between two objects depends directly on the product of their masses and inversely on the square of their separation.
Lens:  optical device designed to converge or diverge light.
Lens equation:  See mirror equation.
Lenz’s law:  magnetic field generated by an induced current opposes the change in field that caused the current.
Lepton:  particle that interacts with other particles only by the electroweak  and gravitational interactions.
Lever arm:  component of the displacement of the force from the axis of rotation in the axis  of rotation in the direction perpendicular to the force.
Light:  electromagnetic radiation with wavelengths between 400 and 700 nm that is visible.
Linear accelerator:  device to accelerate subatomic particles by applying successive electric field.
Linear relationship:  relationship between two variables, x and y, summarized by the equation y= ax + b, where a and b are constant.
Linear restoring force:  force in direction toward equilibrium position that depends linearly on distance from distance from that position.
Liquid:  materials that have fixed volume but whose shape depends on the container.
Lodestone:  naturally occurring magnetic rock.
Longitudinal waves:  wave in which direction of disturbance is the same as the direction of travel of wave.
Loudness:  physiological measure of amplitude of a sound wave; heard on pitch and tone color as well as amplitude.
Lumen:  unit of luminous flux.
Luminance intensity:  measure of light emitted by source in candelas; luminous flux divided by 4pie.
Luminous flux:  flow of light from source measured in lumens.
Luminous object:  object that emits light, as opposed to one that reflects light.
Lux:  unit of luminous flux; one lumen per square meter.

The Letter M:

Machine:  device that changes force needed to do work.
Magnetic field:  space around a magnet throughout which magnetic force exists.
Magnification:  ratio of size of an optical image to the size of the object.
Manipulated variable:  variable that the experimenter can change.
Mass defect:  mass equivalent of the binding energy; m=E/c^ 2
Mass number:  number of nucleons ( protons plus neutrons) in the nucleus of an atom.
Mass spectrometer:  device used to measure the mass of atoms or molecules.
Matter wave:  wave-like properties of particles such as electrons.
Mechanical advantage:  ratio of resistance force to effort force in a machine.
Mechanical energy:  sum of potential and kinetic energy.
Mechanical resonance:  condition at which natural oscillation frequency equals frequency of driving force; amplitude of oscillatory motion at a maximum.
Mechanical wave:  wave consisting of periodic motion of matter; e.g. sound wave or water wave as opposed to electromagnetic wave.
Melting point:  temperature at which substance changes from solid to liquid state.
Meson:  medium mass subatomic particle consisting of combination of a quark and antiquark.
Meter:  SI unit of length.
Mirror equation:  1/do +1/di=1/f, where do is object distance, di is image distance, f is focal length.
Moderator:  material used to decrease speed of neutrons in nuclear reactor.
Momentum:  product of object’s mass and velocity.
Monochromatic light:  light of a single wavelength.
Mutual inductance:  measures the amount of overlap between the magnetic flux produced in one coil and that which passes through a second coil, thus the amount of EMP induced in a secondary coil by the varying flux in the primary coil.
Myopia:  defect of eye, commonly called nearsightedness, in which distant objects focus in front of the retina.

The Letter N:

n-type semiconductor:  semiconductor in which current is carried by electrons.
Net force:  vector sum of forces on object.
Neutral:  object that has no net electric charge.
Neutrino:  chargeless, massless, subatomic particle emitted with beta particles; type of lepton.
Neutron:  subatomic particle with no charge and mass slightly greater than that of proton; type of nucleon.
Newton:  SI unit of force.
Newton’s law of motion:  laws relating force and acceleration.
Node:  point where disturbances caused by two or more waves result in no displacement.
Normal:  perpendicular to plane of interest.
Normal force:  force perpendicular to surface.
Nuclear equation:  equation representing a nuclear reaction.
Nuclear fission:  reaction in which large nucleus splits into two parts, often approximately equal in mass.
Nuclear fusion:  reaction in which two nuclei are combined into one.
Nuclear reaction:  reaction involving the strong force in which the number of protons or neutrons in a nucleus changes.
Nuclear reactor:  device in which nuclear fusion is used to generate electricity.
Nuclear transmutation:  change of one nucleus into another as the result of a nuclear reaction.
Nucleon:  either a proton or a neutron.
Nuclide:  nucleus of an isotope.

The Letter O:

Object:  source of diverging light rays; either luminous or illuminated.
Octave:  interval between two frequencies with a ratio of two to one.
Ohm:  SI unit of resistance; one volt per ampere.
Ohm’s law:  resistance of object is constant, independent of voltage across it.
Opaque:  material that does not transmit light.
Open- pipe resonator:  cylindrical tube with both ends closed and a sound source at one end.

The Letter P:

p-type semiconductor:  semiconductor in which conduction is the result of motion of holes.
Pair production:  formation of particle and antiparticle from gamma rays.
Parabolic mirror:  mirror the shape of a paraboloid  of revolution that has no spherical aberration.
Parallel circuit:  circuit in which there are two or more paths for current flow.
Parallel connection:  connection of two or more electrical devices between two points to provide more than one current path.
Pascal:  SI unit of pressure; one neutron per square meter.
Pascal’s principle:  pressure applied to a fluid is transmitted undiminished throughout it.
Period:  time needed to repeat one complete cycle of motion.
Periodic motion:  motion that repeats itself at regular intervals of time.
Photoelectric effect:  election of electrons from surface of metal exposed to electromagnetic radiation.
Photon:  quantum of electromagnetic waves; particle aspect of these waves.
Photovoltaic cell:  device that converts electromagnetic radiation into electrical energy.
Physics:  study of matter and energy and their relationship.
Piezoelectricity:  electric potential produced by deforming material.
Pigment:  colored material that absorbs certain colors and transmits or reflects others.
Pitch:  perceived sound characteristics equivalent to frequency.
Planck’s constant:  ratio of energy of photon to its frequency.
Plane mirror:  flat, smooth surface that reflects light regularly.
Plasma:  state of matter in which atoms are separated into electrons and positive ions or bare nuclei.
Point object:  object idealized as so small to be located at only one position.
Polarized light:  light in which electric fields are all in same plane.
Position:  separation between object and a reference point.
Position- time graph:  graph of object’s motion that shows how its position depends on clock reading, or time.
Positron:  antiparticle equivalent of electron.
Potential difference:  difference in electric potential between two points.
Potential energy:  energy of object due to its position or state.
Potentiometer:  electrical device with variable resistance; rheostat.
Power:  rate of doing work; rate of energy conversion.
Precision:  degree of exactness in a measurement.
Pressure:  force per unit area.
Primary coil:  transformer coil that, when connected to voltage source, creates varying magnetic flux.
Primary light colors:  red, green, or blue light.
Primary pigment:  yellow, green, or magenta light.
Principal axis:  line connecting center of curvature of spherical mirror with its geometric vertex.  Line perpendicular to plane of lens passing through its center.
Principle of superposition:  displacement due to two or more forces is equal to vector sum of forces.
Projectiles:  motion of objects given initial velocity that then move only under force of  gravity.
Proton:  subatomic particle with positive charge that is nucleus of hydrogen atom.

The Letter Q:

quantized:  a quantity that cannot be divided into smaller increments forever, for which there exists a minimum, quantum increment.
Quantum mechanic:  study of properties of matter using its wave properties.
Quantum model of atom:  atomic model in which only probability of locating electron is known.
Quantum number:  integer ratio of energy to its quantum increment.
Quark:  basic building block of protons, neutrons, other baryons, and mesons.
Quark model:  model in which all particles that interact via the strong interaction are composed of two or three quarks.

The Letter R:

Radiation:  electromagnetic waves that carry energy.
Radioactive decay:  spontaneous change of unstable nuclei into other nuclei.
Radioactive materials:  materials that undergo radioactive decay.
Range of projectile:  horizontal distance between launch point of projectile and where it returns to launch height.
Ray model of light:  light may be represented by straight line along direction of motion.
Ray optics:  study of light using ray model.
Rayleigh criterion:  two optical images are separable if central bright spot of one image falls on first dark band of second.
Real image:  optical image at which rays from object converge.
Receiver:  device that detects electromagnetic waves.
Reference level:  location at which potential energy is chosen to be zero.
Reference point:  zero location in a coordinate system or frame of reference.
Refraction:  change in direction of light ray when passing one medium to another.
Refractive index:  ratio of speed of light in vacuum to that in the medium.
Resistance:  ratio of potential difference across device to current through it.
Resistance force:  force exerted by a machine.
Resistor:  device designed to have a specific resistance.
Responding variable:  variable that changes as result of change in manipulated variable.
Rest energy:  energy due to mass of object; E= mc^  2.
Resultant:  vector sum of two or more vectors.
Right -hand rules:  used to find force on current or moving particle in magnetic field; used to find direction of magnetic field caused by current or of induced EMF.
Rutherford’s model of atom:  nuclear model of atom; essentially all mass in compact, positively- charged object at center, surrounded by electrons.

The Letter S:

Scalar:  quantity, like distance, that has only a magnitude, or size.
Schematic diagram:  representation of electric circuit using symbols.
Scientific notation:  numbers expressed in form  M * 10 ^ n , where 1< M < 10, and n is an integer.
Scintillation:  flash of light emitted when substance is struck by radiation.
Second:  SI unit of time.
Second law of thermodynamics:  heat flow only from region of high temperature o region of lower temperature.
Secondary coil:  transformer coil in which varying EMF is induced.
Secondary light colors:  yellow, cyan, or magenta light.
Secondary pigment:  red, green, or blue pigment.
Self- inductance:  induced EMF produced in coil by changing current.
Semiconductor:  material in which electrical conduction is smaller than that in a conductor, but more than in insulator.
Series circuit:  circuit in which electrical current flows through each component, one after another.
Series connection:  arrangement of electrical devices so that there is only one path through which current can flow.
Short circuit:  low resistance connection between two points, often accidental.
SI:  internationally agreed -upon method of using the metric system of measurement.
Significant digit:  reliable digits reported in a measurement.
Simple harmonic motion:  motion caused by linear restoring that has a period independent of amplitude of motion.
Simple machine:  machine consisting of only one lever, inclined plane, wedge, screw, pulley, or wheel and axle.
Sine:  the ratio of the opposite side and the hypotenuse.
Sliding friction:  force between two surfaces in relative motion.
Slope:  ratio of the vertical separation, or rise to the horizontal separation, or run.
Solid:  state of matter with fixed volume and shape.
Sound level:  quantity measuring logarithm of sound intensity in decibels.
Spark chamber:  device used to detect path of charged subatomic particles by a spark that jumps along path of ionization created in a gas.
Specific heat:  thermal energy needs to change temperature of unit mass of substance one Kelvin.
Spectroscope:  device used to study spectrum of material.
Spectrum:  collection of wavelengths in electromagnetic spectrum.
Speed:  ratio of distance traveled to time interval.
Speed of light:  in vacuum, 2.9979458 * 10^8 m/s.
Spherical aberration:  inability of spherical mirror to focus all parallel rays to a single point.
Standing wave:  wave with stationary nodes.
Static friction:  force that opposes start of motion between two surfaces.
Step- down transformer:  transformer with output voltage smaller than input voltage.
Step- up transformer:  transformer with output voltage larger than input voltage.
Stimulated emission:  emission of photon from excited atom caused by impact fo photon of same energy.
Strong nuclear force:  force of very short range that holds neutrons and protons in nucleus together.
Superconductor:  electrical conductor that has no resistance and low temperatures.
Surface wave:  wave on surface of liquid with characteristics of both longitudinal and transverse waves.
Symmetry:  property that is now charged when operation or reference frame is charged.
Synchrotron:  device to accelerate particles in which particles move in circular path.
System:  defined collection of objects.

The Letter T:

tangent:  the ratio of the opposite side and the adjacent side.
Temperature:  measure of hotness of object on a quantitative scale.  In gases, proportional to average kinetic energy of molecules.
Terminal velocity:  velocity of falling object reached when force of air resistance equals weight.
Test charge:  charge used, in principle, to measure electric field.
Thermal energy:  internal energy.  Sum of kinetic and potential energy of random motion of particles making up object.
Thermal equilibrium:  state between two or more bodies where temperatures do not change.
Thermal expansion:  increase of length or volume of object due to change in temperature.
Thermometer:  device used to measure temperature.
Thermonuclear reaction:  nuclear fusion.
Thin- film interference:  light interference caused by reflection from both front and rear surface of thin layer of liquid or solid.
Timbre:  sound quality or tone color; spectrum of sound frequencies that produce a complete wave.
Time interval:  difference in time between two clock readings.
Tokamak:  type of fusion reactor.
Tone color:  timbre or tone quality.
Torque:  product of force and the lever arm.
Trajectory:  the path followed by projectile.
Transformer:  device to transform energy from one electrical circuit to another by means of mutual inductance between two coils.
Transistor:  semiconductor device that controls large current by means of small voltage changes.
Translucent:  material transmitting light without but distorting its path.
Transmutation:  nuclear change from one element to another.
Transparent:  material transmitting light without distorting directions of waves.
Transverse waves:  wave in which disturbance is perpendicular to direction of travel of wave.
Traveling wave:  moving, periodic disturbance in a medium or field.
Trigonometry:  branch of math that deals with the relationship among angles and sides of triangles.
Trough of wave:  low point of wave motion, where displacement is most negative.

The Letter U:

Uniform acceleration:  constant acceleration.
Uniform circular motion:  motion in a circle of constant radius with constant speed.

The Letter V:

Valence band:  in a solid, the range of energies of electrons that are bound to atoms.
Vector quantity:  quantity having both magnitude (size) and direction.
Vector resolution:  process of finding the effective value of a component in a given direction.
Velocity:  ratio of change in position to time interval over which change takes place.
Velocity- time graph:  plot of velocity of object as a function of time.
Virtual image:  point from which light rays appear to diverge without actually doing so.
Viscous fluid:  fluid that creates force that opposes motion of objects through it.  The force is proportional to object’s speed.
Volatile liquid:  liquid that is easily vaporized.

The Letter W:

Watt:  unit of power, one joule per second.
Wavelength:  distance between corresponding points on two successive waves.
Wave pulse:  single disturbance moving through a medium or field.
Weak boson:  particle that carries or transmits the weak interaction of force.
Weak interaction:  force involved in beta decay of the neutron and atomic nuclei; one aspect of the electroweak force.
Weight:  force of gravity of an object.
Weightlessness:  object in freefall, on which only the gravitational force acts.
Wilson cloud chamber:  chamber containing supersaturated vapor through which ionizing radiation leaves trails of visible droplets.
Work:  product of force and displacement in the direction of the force.
Work function:  energy needed to remove an electron from metal.
Work energy theorem:  work done on object is equal to the change in its kinetic energy.

The Letter X:

X ray:  high- energy photons; high- frequency, short-wavelength electromagnetic waves.
X-ray diffraction:  A complicated technique using x-rays to "create an image" where no lense to focus the light rays is available.
X-ray images:  Images such as photographs or computer enhanced images produced by bombarding a target with x-rays.

The Letter Y:

Young's modulus:  A constant of proportionality associated with the change in length of a material according to its elastic properties.

The Letter Z:

Zero-point energy:  The lowest energy state of molecular vibration

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