AP Physics 2: Algebra-Based Vocabulary

Aberration

A defect in an optical system (such as a lens or mirror) that causes light to not be focused to a single point; includes spherical aberration and chromatic aberration.

Example: "Spherical          occurs because rays far from the optical axis are focused at a different point than rays near the axis."

Absolute pressure

The total pressure at a point in a fluid, equal to the gauge pressure plus atmospheric pressure: P_abs = P_gauge + P_atm.

Example: "A tire gauge reads 32 psi of gauge pressure, but the          inside the tire is about 47 psi when atmospheric pressure is included."

Absolute temperature

Temperature measured on the Kelvin scale, starting at absolute zero (0 K). Many physics laws (ideal gas law, kinetic theory) require absolute temperature.

Example: "The ideal gas law uses          because pressure and volume are proportional to temperature only when measured from absolute zero."

Absolute zero

The lowest possible temperature (0 K or -273.15°C), at which all molecular motion theoretically ceases.

Example: "At         , particles have minimum possible kinetic energy and entropy approaches zero."

Absorption

The process by which an atom or molecule takes in a photon, causing an electron to jump to a higher energy level.

Example: "         of a photon occurs only when the photon's energy exactly matches the difference between two energy levels."

Absorption spectrum

A series of dark lines or bands in an otherwise continuous spectrum, caused by the absorption of specific wavelengths of light by atoms or molecules transitioning to higher energy levels.

Example: "The          of hydrogen shows dark lines at the same wavelengths where its emission spectrum shows bright lines."

Activity (radioactive)

The number of nuclear decays occurring per unit time in a radioactive sample, measured in becquerels (Bq) or curies (Ci): A = λN.

Example: "The          of a sample decreases over time as the number of remaining radioactive nuclei decreases."

Adiabatic process

A thermodynamic process in which no heat is transferred between the system and its surroundings (Q = 0).

Example: "The rapid compression of gas in a diesel engine is approximately an          because it happens too quickly for significant heat exchange."

Alpha decay

A type of radioactive decay in which an unstable nucleus emits an alpha particle (two protons and two neutrons), reducing its atomic number by 2 and mass number by 4.

Example: "Uranium-238 undergoes          to become thorium-234 by releasing a helium nucleus."

Alpha particle

A particle emitted during alpha decay, consisting of two protons and two neutrons (identical to a helium-4 nucleus), with a charge of +2e.

Example: "An          is relatively massive and has low penetrating power — it can be stopped by a sheet of paper."

Alternating current (AC)

Electric current that periodically reverses direction, typically produced by electromagnetic induction in a generator.

Example: "Household electricity in the United States is          at a frequency of 60 Hz."

Ammeter

An instrument used to measure electric current in a circuit, connected in series with the component being measured.

Example: "The          must be placed in series so that all the current flowing through the resistor also flows through it."

Ammeter resistance

The very low internal resistance of an ammeter; ideally zero so that inserting the ammeter does not significantly change the current being measured.

Example: "An ideal ammeter has zero          so that it does not alter the circuit it is measuring."

Ampere

The SI unit of electric current, equal to one coulomb of charge passing a point per second (1 A = 1 C/s).

Example: "A current of 2          means two coulombs of charge flow past a given point each second."

Ampere's law

A law relating the magnetic field around a closed loop to the net electric current passing through the loop: ∮B·dl = μ₀I_enc.

Example: "         can be used to derive the magnetic field inside a long solenoid."

Ampere's right-hand rule

A method for determining the direction of the magnetic field around a current-carrying wire: point the thumb in the direction of current and the fingers curl in the direction of the field.

Example: "Using         , if current flows upward in a wire, the magnetic field wraps counterclockwise when viewed from above."

Angle of deviation

The angle between the incoming ray direction and the outgoing ray direction after passing through a prism or other refracting element.

Example: "Different wavelengths of light have different         s when passing through a prism, which separates white light into a spectrum."

Angle of incidence

The angle between an incoming light ray and the normal (perpendicular) to the surface at the point of contact.

Example: "The law of reflection states that the angle of reflection equals the         ."

Angle of refraction

The angle between the refracted (transmitted) light ray and the normal to the surface at the point where the light crosses into the new medium.

Example: "When light passes from air into water, the          is smaller than the angle of incidence because water has a higher index of refraction."

Angular magnification

The ratio of the angle subtended by the image to the angle subtended by the object when viewed from a reference point; used for magnifying glasses and telescopes.

Example: "A magnifying glass has an          that makes small objects appear larger by increasing the angle they subtend at the eye."

Annihilation

A process in which a particle and its antiparticle collide and convert their combined mass into energy, typically producing two or more photons.

Example: "When an electron and positron undergo         , they produce two gamma-ray photons each with energy of 0.511 MeV."

Anti-reflective coating

A thin film applied to a lens surface, designed so that destructive interference cancels reflected light, increasing transmission.

Example: "An          on eyeglasses reduces glare by using thin-film interference to minimize reflection."

Antimatter

Matter composed of antiparticles that have the same mass as their corresponding particles but opposite charge; when matter and antimatter meet, they annihilate and produce energy.

Example: "A positron is the          counterpart of the electron."

Archimedes' principle

The buoyant force on an object submerged in a fluid equals the weight of the fluid displaced by the object.

Example: "According to         , a steel ship floats because it displaces a volume of water whose weight exceeds the ship's weight."

Atmospheric pressure

The pressure exerted by the weight of the atmosphere on surfaces at a given elevation; approximately 1.01 × 10⁵ Pa (1 atm) at sea level.

Example: "         decreases with increasing altitude because there is less air above pushing down."

Atomic mass number

The total number of protons and neutrons (nucleons) in the nucleus of an atom, denoted A.

Similar definitions: mass number, nucleon number

Example: "Carbon-14 has an          of 14 (6 protons + 8 neutrons)."

Atomic number

The number of protons in the nucleus of an atom, denoted Z; it determines the element's identity and its position in the periodic table.

Example: "All atoms with          6 are carbon atoms, regardless of how many neutrons they have."

Atomic spectrum

The unique set of wavelengths of light emitted or absorbed by a particular element's atoms, serving as a fingerprint for that element.

Example: "Every element has a distinctive          that can be used to identify it in distant stars."

Average kinetic energy

The mean translational kinetic energy of gas molecules, directly proportional to the absolute temperature of the gas: KE_avg = (3/2)kT.

Example: "Doubling the absolute temperature of an ideal gas doubles the          of its molecules."

Avogadro's number

The number of particles (atoms, molecules, or other entities) in one mole of a substance: N_A = 6.022 × 10²³ mol⁻¹.

Example: "         allows us to connect the macroscopic quantity of gas (in moles) to the number of individual molecules."

Back-emf

The electromotive force generated by a motor's spinning coil that opposes the applied voltage, reducing the current through the motor during operation.

Example: "When a motor first starts, there is no         , so the initial current is very large."

Balmer series

The series of spectral lines of hydrogen corresponding to electron transitions from higher energy levels (n ≥ 3) down to n = 2, producing visible light.

Example: "The red Hα line at 656 nm belongs to the          and corresponds to the n = 3 to n = 2 transition."

Barometer

An instrument used to measure atmospheric pressure, typically using a column of mercury or an aneroid cell.

Example: "Torricelli invented the mercury         , which showed that atmospheric pressure supports a column of mercury about 760 mm tall."

Battery

A device that converts chemical energy into electrical energy, maintaining a potential difference (emf) across its terminals to drive current through a circuit.

Example: "A          provides the electromotive force that pushes electrons through the external circuit."

Becquerel

The SI unit of radioactive activity, equal to one nuclear decay per second.

Example: "A sample with an activity of 1000          undergoes 1000 nuclear decays every second."

Bernoulli's equation

A statement of energy conservation for flowing fluids: the sum of pressure, kinetic energy per unit volume, and gravitational potential energy per unit volume remains constant along a streamline.

Example: "         explains why airplane wings generate lift — faster airflow over the top creates lower pressure."

Beta decay

A type of radioactive decay in which a neutron converts to a proton (emitting an electron and antineutrino) or a proton converts to a neutron (emitting a positron and neutrino).

Example: "Carbon-14 undergoes         , transforming into nitrogen-14 by emitting an electron from its nucleus."

Beta particle

A high-speed electron (β⁻) or positron (β⁺) emitted from a nucleus during beta decay.

Example: "A          has moderate penetrating power — it can pass through paper but is stopped by a thin sheet of aluminum."

Binding energy

The energy required to completely separate all the nucleons in a nucleus; equivalently, the energy released when those nucleons come together to form the nucleus.

Example: "Iron-56 has the highest          per nucleon, making it the most stable nucleus."

Binding energy per nucleon

The total binding energy of a nucleus divided by its mass number (A); a measure of nuclear stability — higher values indicate more stable nuclei.

Example: "Nuclei near iron have the highest         , which is why both fission of heavy nuclei and fusion of light nuclei release energy."

Blackbody radiation

Electromagnetic radiation emitted by an idealized object that absorbs all incident radiation; its spectrum depends only on the object's temperature.

Example: "The study of          led Max Planck to propose that energy is quantized, launching quantum mechanics."

Bohr model

A model of the atom in which electrons orbit the nucleus in discrete energy levels, and photons are emitted or absorbed when electrons transition between levels.

Example: "The          successfully predicted the wavelengths in hydrogen's emission spectrum using quantized orbits."

Bohr radius

The radius of the smallest (ground state) electron orbit in the Bohr model of hydrogen: a₀ ≈ 0.0529 nm.

Example: "The          represents the most probable distance of the electron from the proton in a hydrogen atom's ground state."

Boltzmann constant

A fundamental physical constant (k_B = 1.38 × 10⁻²³ J/K) that relates the average kinetic energy of particles in a gas to the temperature of the gas.

Example: "The          appears in the equation KE_avg = (3/2)kT, connecting microscopic particle energy to macroscopic temperature."

Boyle's law

For a fixed amount of ideal gas at constant temperature, the pressure is inversely proportional to the volume: P₁V₁ = P₂V₂.

Example: "         explains why compressing a gas into a smaller container increases its pressure."

Brewster's angle

The angle of incidence at which reflected light is completely polarized; it occurs when the reflected and refracted rays are perpendicular to each other: tan θ_B = n₂/n₁.

Example: "At         , light reflected from a glass surface is fully polarized horizontally, which is why polarized sunglasses reduce glare."

Bright fringe

A region of maximum intensity in an interference or diffraction pattern, caused by constructive interference.

Example: "In a double-slit experiment, a          appears where the path difference is a whole number of wavelengths."

Brightness (bulb)

The perceived light output of a bulb, proportional to the power it dissipates: P = IV = I²R = V²/R.

Example: "The          of a bulb increases when the power delivered to it increases."

Buoyancy

The tendency of a fluid to exert an upward force on an object placed in it, arising from the pressure difference between the top and bottom of the object.

Similar definitions: buoyant effect

Example: "         allows a massive steel ship to float because the ship's hull displaces a large volume of water."

Buoyant force

The upward force exerted by a fluid on any object submerged or floating in it, caused by pressure differences at different depths.

Example: "A block of wood floats because the          from the water equals the weight of the block."

Calorie

A unit of energy equal to approximately 4.186 joules; defined as the energy needed to raise the temperature of one gram of water by one degree Celsius.

Example: "One          is the amount of heat required to warm 1 g of water from 14.5°C to 15.5°C."

Capacitance

The ability of a capacitor to store electric charge per unit voltage, measured in farads (F); C = Q/V.

Example: "Increasing the area of the plates or decreasing the distance between them increases the          of a parallel-plate capacitor."

Capacitor

A device consisting of two conducting plates separated by an insulator (dielectric) that stores energy in an electric field between the plates.

Example: "A          in a camera flash stores electrical energy and releases it rapidly to produce a bright burst of light."

Capacitors in parallel

A configuration in which capacitors are connected across the same two nodes, so each has the same voltage; the total capacitance is the sum: C_total = C₁ + C₂ + ...

Example: "         increase the total capacitance of a circuit because each additional capacitor stores more charge."

Capacitors in series

A configuration in which capacitors are connected end-to-end so the same charge is stored on each; the reciprocals of capacitances add: 1/C_total = 1/C₁ + 1/C₂ + ...

Example: "         result in a total capacitance smaller than any individual capacitor."

Carnot cycle

An idealized thermodynamic cycle consisting of two isothermal and two adiabatic processes, representing the maximum possible efficiency for a heat engine operating between two temperatures.

Example: "No real heat engine can be more efficient than a          operating between the same hot and cold reservoirs."

Carnot efficiency

The maximum possible efficiency of a heat engine operating between two temperature reservoirs: e_Carnot = 1 − T_C/T_H, where temperatures are in kelvins.

Example: "A heat engine operating between 600 K and 300 K has a          of 50%, which no real engine can exceed."

Cathode ray

A beam of electrons emitted from the negative electrode (cathode) in a vacuum tube; used historically to discover the electron.

Example: "J.J. Thomson used         s in his experiments to measure the charge-to-mass ratio of the electron."

Celsius scale

A temperature scale where 0°C is the freezing point of water and 100°C is the boiling point at standard pressure; related to Kelvin by K = °C + 273.15.

Example: "A temperature change of 1 degree on the          is the same magnitude as 1 kelvin."

Center of curvature

The center of the sphere of which a curved mirror is a part; located at a distance equal to the radius of curvature from the mirror's surface.

Example: "For a concave mirror, the          is in front of the mirror, at twice the focal length."

Central maximum

The brightest, widest fringe at the center of a single-slit or double-slit diffraction/interference pattern.

Example: "In single-slit diffraction, the          is twice as wide as the other bright fringes."

Chain reaction

A self-sustaining series of nuclear fission reactions in which neutrons released from one fission event trigger additional fission events.

Example: "A nuclear reactor controls the rate of a          by using control rods to absorb excess neutrons."

Charge conservation

The principle that electric charge can be neither created nor destroyed; the total charge of an isolated system remains constant.

Similar definitions: conservation of charge

Example: "         requires that in any process, the total charge before equals the total charge after."

Charge density

The amount of electric charge per unit length (λ), area (σ), or volume (ρ) of a charged object.

Example: "A uniformly charged sphere has a constant volume          throughout its interior."

Charge quantization

The principle that electric charge exists only in integer multiples of the elementary charge e = 1.6 × 10⁻¹⁹ C.

Example: "         means an object can have a charge of +2e or −3e, but never +1.5e."

Charge-to-mass ratio

The ratio of a particle's electric charge to its mass (q/m); determines the radius of curvature in a magnetic field and was first measured for the electron by Thomson.

Example: "Thomson determined the          of the electron by deflecting cathode rays with electric and magnetic fields."

Charging (capacitor)

The process in which a capacitor in an RC circuit accumulates charge and voltage exponentially approaching the source emf: V(t) = emf(1 − e^(−t/RC)).

Example: "During         , the current starts at its maximum value and decreases exponentially as the capacitor voltage rises."

Charging by conduction

A method of charging an object by direct contact with a charged object, transferring charge from one to the other.

Example: "Touching a neutral metal sphere with a negatively charged rod is an example of         ."

Charging by induction

A method of charging a conductor without direct contact by using a nearby charged object to redistribute charge, then grounding to remove one type of charge.

Example: "         allows you to give an object a charge opposite to the charging object without the two ever touching."

Charles's law

For a fixed amount of ideal gas at constant pressure, the volume is directly proportional to the absolute temperature: V₁/T₁ = V₂/T₂.

Example: "         explains why a balloon expands when heated and shrinks when cooled."

Chromatic aberration

A lens defect in which different wavelengths (colors) of light are focused at slightly different points because the index of refraction varies with wavelength.

Example: "         causes colored fringes around images formed by simple lenses."

Circuit diagram

A schematic representation of an electrical circuit using standardized symbols for components such as resistors, capacitors, batteries, and switches.

Example: "A          uses a zigzag line for a resistor and two parallel lines for a capacitor."

Circular motion in a magnetic field

The curved path of a charged particle moving perpendicular to a uniform magnetic field; the magnetic force provides centripetal acceleration: r = mv/(qB).

Example: "         has a radius that increases with the particle's speed or mass, and decreases with stronger fields or greater charge."

Closed system

A thermodynamic system that can exchange energy (heat and work) but not matter with its surroundings.

Example: "A sealed, rigid container of gas is a          because no molecules can enter or leave."

Coefficient of linear expansion

A material-dependent constant (α) that describes how much a material's length changes per degree of temperature change: ΔL = αL₀ΔT.

Similar definitions: linear expansion coefficient

Example: "Bridges have expansion joints to accommodate changes in length predicted by the          of steel."

Coefficient of volume expansion

A material-dependent constant (β) that describes how much a material's volume changes per degree of temperature change: ΔV = βV₀ΔT. For solids, β ≈ 3α.

Example: "Mercury thermometers rely on the          of mercury to indicate temperature changes."

Coherent light

Light in which all waves have the same frequency and maintain a constant phase relationship, enabling sustained interference patterns.

Example: "A laser produces         , which is essential for producing clear interference and diffraction patterns."

Color

The visual perception associated with specific wavelengths of visible light, ranging from red (~700 nm) to violet (~400 nm).

Example: "The          of light is determined by its wavelength, with shorter wavelengths appearing blue-violet and longer wavelengths appearing red."

Compton scattering

The increase in wavelength of a photon after it collides with and transfers momentum to a free electron, demonstrating the particle nature of light.

Example: "         provided key evidence that photons carry momentum and behave like particles during collisions."

Compton wavelength shift

The change in wavelength of a photon after Compton scattering: Δλ = (h/m_ec)(1 − cos θ), where θ is the scattering angle.

Example: "The          is maximized when the photon scatters at 180° (directly backward)."

Concave lens

A lens that is thinner at the center than at the edges, causing parallel light rays to diverge; also called a diverging lens.

Similar definitions: diverging lens

Example: "A          is used in eyeglasses to correct nearsightedness by spreading light before it enters the eye."

Concave mirror

A curved mirror whose reflective surface curves inward; can form real or virtual images depending on the object's position relative to the focal point.

Example: "A          is used in telescopes to collect and focus light from distant stars."

Conducting sphere

A spherical conductor on which excess charge distributes uniformly over the outer surface and the electric field inside is zero in electrostatic equilibrium.

Example: "On a charged         , all excess charges reside on the surface, and the interior field is zero."

Conduction (thermal)

The transfer of thermal energy through direct molecular collisions in a material, without bulk movement of the material itself.

Similar definitions: thermal conduction, heat conduction

Example: "A metal spoon in hot soup gets warm through          as energy transfers from molecule to molecule."

Conduction rate

The rate at which heat is transferred through a material by conduction: Q/t = kA(ΔT)/L, where k is thermal conductivity, A is area, and L is thickness.

Example: "The          through a wall increases with greater temperature difference, larger area, or thinner walls."

Conductor

A material that allows electric charge to flow freely through it due to the presence of free electrons; metals are common examples.

Example: "Copper wire is an excellent         , which is why it is widely used in electrical wiring."

Conservation of charge (circuits)

In a circuit, charge is neither created nor destroyed; the current entering any junction equals the current leaving it (Kirchhoff's junction rule).

Example: "         guarantees that if 3 A enters a junction and 1 A flows through one branch, then 2 A must flow through the other."

Conservation of energy

The principle that the total energy of an isolated system remains constant; energy can change form but cannot be created or destroyed.

Example: "         in a circuit means the energy supplied by the battery equals the total energy dissipated in all resistors."

Conservation of nucleon number

The principle that the total number of nucleons (protons + neutrons) is conserved in every nuclear reaction.

Example: "         requires that the sum of mass numbers on the reactant side equals the sum on the product side."

Constructive interference

The superposition of two or more waves that are in phase, resulting in a combined wave with greater amplitude than either individual wave.

Example: "In the double-slit experiment, bright fringes appear where          occurs between waves from the two slits."

Continuity equation

A statement of mass conservation for fluid flow: the product of cross-sectional area and fluid speed is constant along a pipe (A₁v₁ = A₂v₂).

Example: "The          explains why water speeds up when you partially cover the end of a garden hose."

Continuous spectrum

A spectrum containing all wavelengths within a range, with no gaps; produced by hot, dense objects (solids, liquids, or dense gases).

Example: "An incandescent light bulb produces a          because its hot filament emits light at all visible wavelengths."

Convection

The transfer of thermal energy by the bulk movement of a heated fluid (liquid or gas), driven by density differences.

Example: "Warm air rising above a heater and cool air sinking near a window is an example of         ."

Conventional current

The direction of current flow defined as the direction positive charges would move — from high potential to low potential — opposite to the actual flow of electrons.

Example: "         flows from the positive terminal of a battery through the circuit to the negative terminal."

Converging lens

A lens that is thicker at the center than at the edges, causing parallel light rays to converge to a focal point; also called a convex lens.

Example: "A magnifying glass is a          that focuses sunlight to a small, bright spot."

Converging mirror

A concave mirror that converges parallel light rays to a real focal point in front of the mirror.

Similar definitions: concave mirror

Example: "A satellite dish acts like a         , focusing incoming signals to a detector at the focal point."

Convex mirror

A curved mirror whose reflective surface curves outward, always producing virtual, upright, and reduced images.

Example: "Passenger-side car mirrors are          mirrors that provide a wider field of view."

Coulomb

The SI unit of electric charge; one coulomb equals the charge of approximately 6.24 × 10¹⁸ protons or electrons.

Example: "A current of one ampere means one          of charge passes a given point every second."

Coulomb's constant

The proportionality constant in Coulomb's law: k = 8.99 × 10⁹ N·m²/C², also written as k = 1/(4πε₀).

Example: "         is used to calculate the electric force between two point charges."

Coulomb's law

The electric force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them: F = kq₁q₂/r².

Example: "         shows that doubling the distance between two charges reduces the electric force to one-quarter of its original value."