List of Physics Terms

Hugh Fox Physics Terms

Absolute Zero of Temperature – temperature at which a gas would exert no pressure

Absorbed Dose (D) – total energy absorbed per unit mass of tissue

Acceleration (a) – rate of change of velocity

Accuracy – An indication of how close a measurement is to the accepted value  (a measure of correctness).

Acoustic Impedance (Z) – the product of the density of a substance and the speed of sound in that substance

Active Solar Heater (solar panel) – designed to capture as much thermal energy as possible by allowing solar radiation to heat water running through a pipe in the panel.

Activity (A) – number of radioactive disintegrations (decays) per unit time

Adiabatic – a process that occurs without the transfer of thermal energy (Q = 0)

Albedo (α) – fraction of the total incoming solar radiation received by a planet that is reflected back out into space (OR: ration of total solar radiation power scattered by a planet to total solar radiation received by a planet) (NOTE: global annual mean albedo is 0.3 for Earth)

Alpha Particle (α) – helium nucleus (2 protons + 2 neutrons)

Amplitude – maximum displacement from the mean position

Analog – technique involving codes or signals that can take on a large number of different values between given limits – analog signals vary continuously with time

Analyzer – polarizer used to detect polarized light

Angular magnification – Ratio of the angle the image subtends at the eye to the angle the object subtends at the eye.

Antinode – locations of maximum constructive interference on a standing wave

Artificial (Induced) Transmutation – when a nucleus is bombarded with a nucleon, an alpha particle or another small nucleus, resulting in a nuclide with a different proton number (a different element).

A-scan – amplitude modulated scan – presents the information from an ultrasound probe as a graph of signal strength versus time

Asia-Pacific Partnership on Clean Development and Climate (APPCDC) – agreement between six countries (representing approximately 50% of the worlds energy use – Australia, China, India, Japan, Republic of Korea, and USA) to “work together and with private sector partners to meet goals for energy security, national air pollution reduction, and climate change in ways that promote sustainable economic growth and poverty reduction.”

Attenuation – the lessening of the intensity of radiation due to absorption by a material or a spreading out of the beam

Attenuation Coefficient (μ) – ratio of the natural log of 2 to the half-value thickness (a constant that allows us to calculate the intensity of X-rays given any thickness of material)

Avogadro constant (NA) – The number of atoms in 0.012 kg of 12C ( = 6.02 x 1023).

Bainbridge Mass Spectrometer – a device used to determine atomic masses – consists primarily of a velocity selector and a magnetic chamber

Balanced Risk – an attempt to balance the risk of exposure to ionizing radiation with the benefits of its use in diagnosis and treatment of illness

Beta Negative Particle (β) – positron (antielectron)

Beta Positive Particle (β+) – electron

Binary Number – number written using base-2

Binding Energy – energy released when a nuclide is assembled from its individual components (OR: energy required when nucleus is separated into its individual components)

Binding Energy per Nucleon – energy released per nucleon when a nuclide is assembled from its individual components (OR: energy required per nucleon when nucleus is separated into its individual components)

Biological Half-life (TB) – time taken for half the number of ingested radioactive nuclei in the body to be removed by natural bodily (chemical) processes

Bit – binary digit that can only take one of two possible values (1 or 0; ON or OFF; High or Low; True or False)

Black-Body Radiation – radiation emitted by a “perfect” emitter of radiation

Boiling – a phase change of a liquid into a gas that occurs at a fixed temperature

Brewster’s Law – When light is incident on a surface at such an angle that the reflected and transmitted rays are perpendicular, the reflected ray is completely plane polarized.  Then the index of refraction of the substance is equal to the tangent of the angle of incidence. (n = tan )

B-scan – brightness modulated scan – uses the signal strength from an ultrasound probe to affect the brightness of a dot of light on a screen

Bumps and Pits – high and low areas of a CD used to encode data (NOTE: Destructive interference occurs when light is reflected from the edge of a pit.)

Byte – eight separate bits of information

Capacitance (C) – ratio of charge stored in a device to the potential difference across the device (C = q / V)

Chain Reaction – neutrons released from one fission reaction go on to initiate further reactions (NOTE: Only low-energy neutrons (≈ 1 eV) favor nuclear fission.)

Change in Gravitational Potential Energy (ΔEp) – product of an object’s mass times the gravitational field strength times the change in height

Charge-Coupled Device (CCD) – silicon ship divided into small areas called pixels (NOTE: CCDs are used for image capturing in a large range of the electromagnetic spectrum.  They are used in digital cameras, video cameras, medical X-ray imaging, and telescopes, such as the Hubble Telescope.)

Chromatic aberration – Rays of different frequencies do not all converge at the same focal point due to dispersion by the lens.

Coefficient of Volume Expansion (γ) – fractional change in volume per degree change in temperature (γ = ΔV / (V0 ΔT))

Compression – area of high pressure in a longitudinal wave

Computed Tomography (CT) Scan – an X-ray imaging technique – X-rays and detectors are rotated around a patient and a computer combines the information to produce a 3-D interior picture

Conductor – material through with electric charge flows freely

Constructive Interference – superposition of two or more pulses or waves in phase

Control Rods – are used to remove any excess neutrons to ensure the fission reaction continues safely (eg. – may be made of cadmium or boron steel)

Controlled Nuclear Fission – used for power production

Coulomb interaction (Coulomb force, electrostatic force) – electrostatic force of repulsion between the protons in the nucleus

Coulomb’s Law – The electric force between two point charges is directly proportional to the product of the two charges and inversely proportional to square of the distance between them, and directed along the line joining the two charges.  (F = k q1 q2 / r2)

Crest – top of a transverse wave

Critical Damping – when a resistive force is applied to an oscillating system that causes the particle to return to zero displacement in a minimum amount of time

Critical Mass – minimum mass of radioactive fuel block needed for a chain reaction to occur

Damping – the result of a force that acts on a system in the opposite direction to the direction of motion of the oscillating particle (NOTE: this force is a dissipative force)

Davisson-Germer Experiment – an experiment showing that electrons are scattered off crystals of nickel and interfere with each other – also know as “electron diffraction”  (NOTE: This experiment is evidence for the existence of matter waves.)

de Broglie Hypothesis – All particles can behave like waves whose wavelength is given by λ = h/p where h is Planck’s constant and p is the momentum of the particle.

Decimal Number – number written using base-10

Degraded Energy – In any process that involves energy transformations, the energy that is transferred to the surroundings (thermal energy) is no longer available to perform useful work.

Derived Units – units that are combinations of fundamental units.  These combinations may or may not have a separate name. (eg. 1 kg m/s2 = 1 N)

Destructive Interference – superposition of two or more pulses or waves out of phase

Diffraction – the bending or spreading of a wave when it passes through a small opening (aperture) or around a barrier

Digital – technique involving codes or signals made up of a large number of binary digits (bits) that can each take only one of two possible values

Dioptre – The unit of power for a converging lens: 1 dioptre = 1 m-1

Direction of a Magnetic Field – the direction that the North pole of a small test compass would point if placed in the field (N to S)

Dispersion – The separating of white light into its component colors due to refraction.

Displacement (for waves) – distance in a particular direction of a particle from its mean position

Displacement (s) – distance traveled from a fixed point in a particular direction

Doppler Effect – The change of frequency of a wave due to the movement of the source or the observer relative to the medium of wave transmission.

Dose Equivalent (H) – product of quality factor and absorbed dose  which is an attempt to measure the radiation damage that actually occurs in tissues

Effective Half-life (TE) – time taken for the number of radioactive nuclei present in the body to halve

Efficiency (eff) – The ratio of the useful energy (or power or work) output to the total energy (or power or work) input.

Elastic Collision – a collision in which kinetic energy is conserved

Electric Current (I) –  current is defined in terms of the force per unit length between parallel current-carrying conductors (NOTE: one ampere of current is the amount of current in each of two infinitely long straight wires one meter apart experiencing a magnetic force per unit length of 2 x 10-7 newtons)

Electric Field Strength (E) – Electric force per positive unit test charge  (E = F/q)

Electric Potential (V) – work done per unit charge moving a small positive test charge in from infinity to a point in an electric field. (V = W/q)  (V = kq/r) (NOTE: the work done is path independent)

Electric Potential Difference (ΔV) – electric potential energy difference per unit charge between two points in an electric field (ΔV = ΔEe / q   OR   ΔV = W / q)

Electric Potential Energy (Ee)- energy that a charge has due to its position in an electric field

Electromotive Force (emf) (ε) – total energy per unit charge supplied by the battery around a circuit (ε = ΔEe/q    OR   ε = W/q)

Electron in a Box Model – a model of the atom useful for explaining the origin of atomic energy levels:  The model assumes that, if an electron is confined to move in one dimension by a box, the de Broglie waves associated with the electron will be standing waves of wavelength 2L/n where L is the length of the box and n is a positive integer.  Further, the kinetic energy of the electron in the box is n2h2/(8meL2)

Electronvolt (eV) – energy gained by an electron moving through an electric potential difference of one volt.  (OR: Work done moving an electron through an electric potential difference of one volt.)  (1 eV = 1.60 x 10-19 J)

Emissivity (ε) – ratio of power emitted by an object to the power emitted by a black-body at the same temperature.

Endoscope – tube with a collection of optical fibers using lasers to look inside the human body

Energy Density (of a fuel) – the ratio of the energy released from the fuel to the mass of the fuel consumed

Enhanced (Anthropogenic) Greenhouse Effect – Human activities, mainly related to the burning of fossil fuels, have released extra carbon dioxide into the atmosphere, thereby enhancing or amplifying the greenhouse effect (a possible cause of global warming).

Entropy – a system property that expresses the degree of disorder in the system

Equipotential Surface – a surface on which the potential is the same everywhere

Escape Speed (v­­esc ) – minimum speed an object must have at the surface of a planet in order to escape the gravitational field of the planet

Evaporation – when faster moving molecules have enough energy to escape from the surface of a liquid that is at a temperature less than its boiling point, leaving slower moving molecules behind which results in a cooling of the liquid

Exposure (X) – charge per unit mass produced as a result of ionization

Far point – Distance between the eye and the furthest object that can be brought into focus.

Faraday’s Law – The emf induced by a time changing magnetic field is proportional to the rate of change of the flux linkage. (ε α  N ΔΦ/Δt)

Field (Field of Force) – a region of space where a mass or charge experiences a force

First Law of Thermodynamics (Q = ΔU + W) – The thermal energy transferred to a system from its surroundings is equal to the work done by the system plus the change in internal energy of the system.  (an application of the principle of conservation of energy)

Focal length – Distance between the focal point and the center of the lens.

Focal point – Location on the principal axis where parallel light rays converge after passing through the lens.

Forced Oscillations – a system may be forced to oscillate at any given frequency by an outside driving force that is applied to it

Fossil Fuels – coal, oil, and natural gas (NOTE: Industrialization led to a high rate of energy usage leading to industry being developed near large deposits of fossil fuels.)

Frequency (f) – number of oscillations per unit time

Fuel – source of energy (in a useful form)

Fuel Enrichment – process by which the percentage composition of a desirable radioactive nuclide (eg. – uranium-235) is increased in order to make nuclear fission more likely

Fundamental (First Harmonic) – lowest frequency mode of vibration of a standing wave

Fundamental Units – seven basic units of the SI measurement system: kilogram, second, mole, meter, ampere, Kelvin, candela.

Gamma Radiation (γ) – high energy (high frequency) electromagnetic radiation

Geiger-Marsden experiment – also known as the Rutherford Alpha Particle Scattering or Gold Foil Experiment

Global Warming – increase in mean temperature of the Earth in recent years

Gravitational Field Strength (g) – gravitational force per unit mass exerted on a small or point mass   (g = Fg / m)

Gravitational Potential (V) – the work done per unit mass bringing a small point mass in from infinity to a point in a gravitational field (NOTE: the work done is path independent)

Gravitational Potential Energy (EP) – the work done bringing a small point mass in from infinity to a point in a gravitational field (NOTE: the work done is path independent)

Greenhouse Effect –Short wavelength radiation received from the Sun causes the Earth’s surface to warm up.  Earth will then emit longer wavelength radiation (infra-red) which is absorbed by some gases (eg. – methane, water vapor, carbon dioxide, nitrous oxide) in the atmosphere and re-radiated in all directions.  This extra warming of the Earth’s atmosphere is known as the Greenhouse Effect.

Half-Value Thickness (x1/2) – the thickness of a material needed for a beam (of X-rays) to be attenuated (reduced in intensity) by 50%

Heat Exchanger – This allows the nuclear reactions to occur in a place that is sealed off from the rest of the environment. Reactions increase temperature in the core and this thermal energy is transferred to water and the steam that is produced turns the turbines.

Heisenberg Uncertainty Principle – Conjugate quantities (position-momentum or time-energy) cannot be known precisely at the same time.  (NOTE: There is a link between the uncertainty principle and the de Broglie hypothesis.  For example, if a particle has a uniquely defined de Broglie wavelength, then its momentum is known precisely but all knowledge of its position is lost.)

Ideal Ammeter – one with zero internal resistance – must be placed in series

Ideal Gas – a gas that follows the ideal gas equation of state (PV = nRT) for all values of P, V, and T (NOTE: an ideal gas cannot be liquefied)

Ideal Voltmeter – one with infinite internal resistance – must be placed in parallel

Impedance Matching – a mechanism for transmitting, rather than reflecting, as much of the sound energy from the air to the cochlea as possible – without this mechanism for pressure transformation between media of different densities (air and fluid), most sound would be reflected rather than transmitted into the cochlear fluid

Impulse (J) – change in momentum

Inelastic Collision – a collision in which kinetic energy is not conserved

Inner Ear (especially Cochlea) – converts the oscillations in the fluid of the inner ear into electrical signals that are sent along the auditory nerve to the brain

Insulator – material through which electric charge does not flow freely

Insulator – material through which electric charge does not flow freely

Intensity (I) – power per unit area (NOTE: for a wave, its intensity is proportional to the square of its amplitude)

Intergovernmental Panel on Climate Change (IPCC) – panel established by the World Meteorological Organization and the United Nations Environment Programme in 1988 in which hundreds of governmental scientific representatives from more than one hundred countries regularly assess the up-to-date evidence from international research into global warming and human induced climate change.

Internal Energy of a substance (U) – The total potential energy and random kinetic energy of the molecules of the substance.

Internal Resistance (r) – the resistance supplied by the materials within the device (eg. battery or meter)

Isobaric – a process that occurs at constant pressure (ΔP = 0)

Isochoric (Isovolumetric) – a process that occurs at constant volume (ΔV = 0)

Isothermal – a process that occurs at constant temperature (ΔT = 0)

Isotope – nuclei with the same number of protons (Z) but different number of neutrons (N)

Kelvin scale of Temperature – an absolute scale of temperature in which 0 K is the absolute zero of temperature

Kepler’s Third Law – the ratio of the orbital period squared to the average orbital radius cubed is constant for all planets

Kinetic Energy (EK) – product of ½ times the mass of an object times the square of an object’s speed

Kyoto Protocol – an amendment to the United Nations Framework Convention on Climate Change in which signatory countries agree to work towards achieving a stipulate reduction in greenhouse gas emissions (NOTE: Notable non-signers are the United States and Australia.)

Law of Conservation of Electric Charge – The total electric charge of an isolated system remains constant.

Law of Conservation of Linear Momentum – The total momentum of an isolated system (no external forces) remains constant.

Law of Reflection – The angle of incidence is equal to the angle of reflection when both angles are measured with respect to the normal line (and the incident ray, reflected ray and normal all lie in the same plane).

Least-Significant Bit (LSB) – right hand digit representing the smallest power

Lenz’s Law – The direction of an induced emf is such that it produces a magnetic field whose direction opposes the change in magnetic field that produced it. (NOTE: This is the negative sign added to Faraday’s law.  ε= – N ΔΦ/Δt)

Light-Dependent Resistor (LDR) – sensor whose resistance depends on amount of light shining on its surface – an increase in light causes a decrease in resistance

Linear magnification – The ratio of the height of the image to the height of the object.

Linear Momentum (p) – product of mass and velocity

Longitudinal Wave – wave in which the direction of motion of the energy transfer (the wave) is parallel to the direction of motion of the particles of the medium (NOTE: sound waves are longitudinal)

Loudness – the response of the ear to intensity

Magnetic Flux (Φ) – product of the magnetic field strength and a cross-sectional area and the cosine of the angle between the magnetic field and the normal to the area   (Φ = B A cosθ)

Magnetic Flux Linkage – product of the magnetic flux through a single coil and the total number of coils (flux linkage = N Φ)

Magnification – ratio of the length of the image on the CCD to the length of the object

Magnitude of a Magnetic Field (magnetic field strength, magnetic field intensity, magnetic flux density) (B) – ratio of magnetic force on a current carrying conductor to the product of the current and length of wire and sine of the angle between the current and the magnetic field  (B = FB / Ilsinθ) (OR: ratio of magnetic force on a charged particle to the product of the charge and its velocity and the sine of the angle between the velocity and the magnetic field)  (B = FB / qvsinθ)

Malus’ Law – The intensity of transmitted polarized light is equal to the product of the incident intensity and the square of the cosine of the angle between the transmission axes of the polarizer and the analyzer. (I = Io cos2 θ )

Mass Defect – difference between the mass of the nucleus and the sum of the masses of its individual nucleons

Matter Waves – All moving particles have a “matter wave” associated with them whose wavelength is the de Broglie wavelength.

Middle Ear – converts the oscillations of the ear drum into oscillations in the fluid of the inner ear at the oval window

Millikan’s Stopping Potential Experiment – an experiment utilizing reverse voltage raised to such a level (stopping potential Vs) that it stops all emitted photoelectrons (NOTE: This experiment is used to test the Einstein model of the explaining the photoelectric effect.)

Moderator – Most neutrons released in fission are fast neutrons, so a moderator is used to reduce their energy down to thermal levels to ensure that the fission is self-sustaining. (e.g. – may be made of solid graphite or steam)

Molar Mass – The mass of one mole of a substance.

Mole – An amount of a substance that contains the same number of atoms as 0.012 kg of 12C.

Monochromatic – Waves of a single frequency (wavelength).

Most-Significant Bit (MSB) – left hand digit representing the largest power

N = N0e-λt  OR A = λ N0e-λt  (as an exponential function)

Natural Frequency of Vibration – when a system is displaced from equilibrium and allowed to oscillate freely, it will do so at its natural frequency of vibration

Near point – Distance between the eye and the nearest object that can be brought comfortably into focus. “least distance of distinct vision”

Negative Temperature Coefficient (NTC) Thermistor – sensor whose resistance depends on its temperature – an increase in temperature causes decrease in resistance

Neutron Number (N) – number of neutrons in nucleus (N = A – Z)

Newton’s First Law of Motion – An object at rest remains at rest and an object in motion remains in motion at a constant speed in a straight line unless acted on by an unbalanced force.

Newton’s Second Law of Motion – An unbalanced force will cause an object to accelerate in the direction of the net force.  The acceleration of the object is proportional to the net force and inversely proportional to its mass. (F­net = ma or Fnet = Δ p/Δ t (net force = rate of change of momentum))

Newton’s Third Law of Motion – When two bodies A and B interact (push or pull), the force that A exerts on B is equal and opposite to the force that B exerts on A.

Newton’s Universal Law of Gravitation – The force of gravity between two objects is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them and acts along a line joining their centers.  (NOTE: The objects are point masses.  If they are not point masses but are very far apart, that is, the distance between them is very much greater than their radii, they can be treated like point masses.)

Node – locations of constant complete destructive interference on a standing wave

Non-Ohmic Device – A device that does not obey Ohm’s law (that is, whose resistance does not remain constant). (eg – filament lamp)

Non-renewable Energy Source – source of energy that can be used up (eg. – coal, oil, natural gas, nuclear)

Nuclear Fission – a heavy nucleus splits into two smaller nuclei of roughly equal mass

Nuclear Fusion – two light nuclei join to form a heavier nuclei (NOTE: This is the main source of the Sun’s energy.)

Nuclear Magnetic Resonance (NMR) Imaging – medical imaging technique that involves the use of a non-uniform magnetic field in conjunction with a large uniform field to cause nuclei to broadcast radio waves used to image the patient

Nucleon – a proton or neutron (NOTE: Do not say “a particle in the nucleus” since that would include quarks as well.)

Nucleon Number (Mass Number) (A) – number of nucleons (protons + neutrons) in nucleus

Nuclide – a particular type of nucleus with a certain number of protons and neutrons

Ohm’s Law – For a conductor at constant temperature, the current flowing through it is proportional to the potential difference across it (NOTE: R = V/I is not a statement of Ohm’s Law)

Ohmic Device – A device that obeys Ohm’s law for a wide range of potential differences (that is, whose resistance remains constant). (eg – resistor)

Optically Active Substance – one that rotates the plane of polarization of the light that passes through it (OR: one that changes the plane in which the electric field vector of the light vibrates)

Oscillating Water Column (OWC) Ocean-Wave Energy Converter – device built on land that uses the kinetic energy of waves to force air in and out of a turbine which generates electrical energy

Ossicles – three small bones in the inner ear – malleus, incus and stapes (hammer, anvil and stirrup)

Outer Ear – shaped to channel air vibrations (sound) to the tympanic membrane

Path Difference – difference in the distances two waves must travel from their sources to a given point

Period (T) – time taken for one complete oscillation (cycle) (OR: time taken for one cycle to pass a given point)

Phase Difference – difference in phase between the particles of two oscillating systems

Photoelectric Effect – the emission of electrons from a metal when electromagnetic radiation of high enough frequency falls on the surface

Photon – a discrete unit or package of light energy

Photovoltaic Cell (solar cell, photocell) – converts a portion of the solar radiation directly into a potential difference (voltage) using a semiconductor  (NOTE: A typical photovoltaic cell produces a very small voltage and is not able to provide much current so is usually used to run electrical devices that do not require a great deal of energy.)

Physical Half-life (TP) (same as T1/2) –

Piezoelectric Crystals – quartz crystals that change shape when an electric current flows and can be used with AC voltage to produce and detect ultrasound

Pixel – small area of a CCD that acts as a capacitor

Polarized Light – light in which the electric field vector vibrates in one plane only

Polarizer – device that produces plane polarized light from an unpolarized beam

Potential Divider – two resistors placed in series that divide up the battery’s potential difference (R1 / R2 = V1 / V2)

Power (P) – The rate at which work is done or the rate at which energy is transferred.

Power of a converging lens – The reciprocal of the focal length of the lens

Precision – An indication of the agreement among a number of measurements made in the same way (a measure of exactness).

Pressure (P) – force per unit area acting on a surface

Principal axis – Line through the focal point of a lens and the center of the lens.

Principle of Conservation of Energy – The total energy of an isolated system (no external forces) remains constant.  (OR – Energy can be neither created nor destroyed but only transformed from one form to another or transferred from one object to another.)

Principle of Superposition – When two or more waves meet, the displacement of the resultant wave is the vector sum of the displacements of the component waves.

Proton Number (Atomic Number) (Z) – number of protons in nucleus

Pulse Oximetry – laser technique for measuring the oxygen content of the blood by shining red or infrared light through a thin part of a patient’s anatomy

Quantum Efficiency (of a pixel) – ratio of the number of photoelectrons emitted to the number of photons incident on the pixel

Radial Field – field that extends radially (like the electric field around a point charge or the gravitational field around a planet)

Radiation Dosimetry – techniques for measuring the amount of ionizing radiation

Radioactive Decay – when an unstable nucleus emits a particle (alpha, beta, gamma) (NOTE: Radioactive decay is both a random and a spontaneous process.) (NOTE: The rate of radioactive decay decreases exponentially with time.)

Random Uncertainty – An uncertainty produced by unknown and unpredictable variations in the experimental situation, such as temperature fluctuations and estimations when reading instruments.  (Affects the precision of results – Can be reduced by taking repeated trials but not eliminated – shows up as error bars on a graph)

Rarefaction – area of low pressure (expansion) in a longitudinal wave

Ray – line drawn perpendicular to a wavefront indicating the direction of motion of the energy transfer

Rayleigh Criterion – For two sources to be “just resolved,” the first minimum of one diffraction pattern is located on top of the central maximum of the other diffraction pattern.

Real Gas – a gas that does not follow the ideal gas equation of state for all values of P, V, and T (Note: a real gas can approximate an ideal gas in some circumstances)

Real image – Image formed when light rays actually converge on a location and can be projected onto a screen.

Relative Biological Effectiveness (RBE) (or Quality Factor) – for the same absorbed dose, this measures the relative effectiveness of different radiations in destroying cells (OR constant of proportionality between dose equivalent and absorbed dose)

Renewable Energy Source – source of energy that cannot be used up (eg. –hydroelectric, photovoltaic cells, active solar heaters, wind, biofuels) (NOTE: In most instances, the Sun is the primary energy source for world energy.)

Resistance (R) – ratio of potential difference applied across a piece of material to the current through the material (R = V/I)

Resistor – device with a constant resistance (Ohmic device) over a wide range of potential differences

Resolution – ability to distinguish between two sources of light

Resonance – a transfer of energy in which a system is subject to an oscillating force that matches the natural frequency of the system resulting in a large amplitude of vibration

Root Mean Square (rms) Value of an Alternating Current (or Voltage) – the value of the direct current (or voltage) that dissipates power in a resistor at the same rate (NOTE: The rms value is also known as the “rating.”)

Sankey Diagram – energy flow diagram

Scalar – a quantity with magnitude only

Schrödinger Model of the Atom – This model assumes that electrons in the atom may be described by wavefunctions.  The electron has an undefined position, but the square of the amplitude of the wavefunction gives the probability of finding the electron at a particular point.

Second Law of Thermodynamics – The overall entropy of the universe is increasing.  (OR – All natural processes increase the total entropy of the universe.) (NOTE: The second law implies that thermal energy cannot spontaneously transfer from a region of low temperature to a region of high temperature.)

Second Law of Thermodynamics – Thermal energy may be completely converted to work in a single process, but that continuous conversion of this energy into work requires a cyclical process and the transfer of some energy from the system.

Selective Frequency Loss – conductive loss of hearing for a particular range of frequencies

Simple Harmonic Motion (SHM) – motion that takes place when the acceleration of an object is proportional to its displacement from its equilibrium position and is always directed toward its equilibrium position (NOTE: this motion is defined by the equation     a = -ω2x)

Snell’s Law – The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for a given frequency.

Sound Intensity – amount of energy that a sound wave brings to a unit area every second (OR power incident per unit area)  (NOTE: Intensity depends on the square of the amplitude of the sound wave.) (NOTE: There is a logarithmic response of the ear to intensity.)

Sound Intensity Level (IL) –– ten times the common logarithm of the ratio of the intensity of a sound to the sound intensity at the threshold of hearing  (measured in decibels (dB))

Specific Heat Capacity (c) – amount of energy per unit mass required to raise the temperature of a substance by 1K

Specific Latent Heat (L) – amount of energy per unit mass required to change phase of a substance at constant temperature and pressure

Speed (u,v) – rate of change of distance

Spherical aberration – Rays parallel to the principal axis do not all converge at the focal point.

Standing (stationary) wave – resultant wave formed when two waves of equal amplitude and frequency traveling in opposite directions in the same medium interfere (NOTE: does not involve a transfer of energy) (NOTE: points on the wave have varying amplitudes)

Stefan-Boltzmann Law – The total power radiated by a black-body per unit area is proportional to the fourth power of the temperature of the body. (power = σAT4)

Strain Gauge – sensor whose output voltage depends on any small extension or compression that occurs which results in a change of length – an increase in strain force causes an increase in resistance

Surface Heat Capacity (CS) – energy required to raise the temperature of a unit area of a planet’s surface by 1 K.  (CS = Q / (A ΔT))

Systematic Error – An error associated with a particular instrument or experimental technique that causes the measured value to be off by the same amount each time. (Affects the accuracy of results – Can be eliminated by fixing source of error – shows up as non-zero y-intercept on a graph)

Temperature (T) – The property that determines the direction of thermal energy transfer between two objects.

Thermal Capacity (C) – amount of energy required to raise the temperature of a substance by 1K

Thermal Energy (Heat) (Q) – energy transferred between two substances by non-mechanical means (such as conduction, convection and radiation)

Thermal Equilibrium – two objects are in thermal equilibrium when they are at the same temperature so that there is no transfer of thermal energy between them

Threshold Frequency (f0) – minimum frequency of light needed to eject electrons from a metal surface

Tinnitus – temporary deafness across the frequency range due to short-term exposure to loud sounds (“ringing” in the ears)

Translational Equilibrium – net force acting on a body is zero

Transverse Wave – wave in which the direction of motion of the energy transfer (the wave) is perpendicular to the direction of motion of the particles of the medium (NOTE: light waves are transverse) (NOTE: transverse waves cannot be propagated in gases)

Traveling Wave (Progressive Wave, Continuous Wave) – series of periodic pulses that involves a transfer of energy although there is no net motion of the medium through which the wave travels

Trough – bottom of a transverse wave

Tympanic Membrane – ear drum

Ultrasound Scan – medical imaging technique in which high frequency (MHz) sound waves are transmitted and reflected from soft tissue

Uncontrolled Nuclear Fission – used for nuclear weapons

Unified Atomic Mass Unit – 1/12th the mass of a carbon-12 nucleus

Vector – a quantity with both a magnitude and a direction

Velocity (u,v) – rate of change of displacement

Virtual image – Image formed by light rays that only appear to converge on a location and cannot be projected onto a screen.

Wave Pulse – single oscillation or disturbance in a medium

Wave Speed (v) – speed of transfer of the energy of the wave

Wavefront – collection of neighboring points on a wave that are in phase

Wavelength (λ) – shortest distance along the wave between two points in phase with one another  (OR: distance traveled by the wave in one period)

Wave-Particle Duality: Both matter and radiation have a dual nature.  They exhibit both particle and wave properties.

Weightlessness in deep space – a sensation of weightlessness due to the minimal pull of gravity very far from any massive object

Weightlessness in free-fall – a sensation of weightlessness because a person is falling freely toward the Earth, hence there is no normal force (reaction force) acting on the person due to gravity

Weightlessness in orbital motion – a sensation of weightlessness due to the spacecraft and all objects in it being in constant free-fall together as they circle Earth

Work Function (Φ) – minimum energy needed to eject electrons from the surface of a metal

Handout at:


One response to “List of Physics Terms

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