KCET key terms

An expression showing each base quantity raised to the power needed to represent a physical quantity, such as force being mass times length divided by time squared. It is used to check equation consistency and convert units.

A method that uses the dimensions of physical quantities to test whether an equation is correct, to derive relations between quantities, and to convert values between systems of units. It cannot determine dimensionless numerical constants.

The seven foundational units from which all other SI units are built: metre, kilogram, second, ampere, kelvin, mole, and candela. Derived units such as newton and joule are formed by combining these.

The curved path of an object launched into the air that moves under gravity alone, with constant horizontal velocity and uniformly accelerated vertical velocity. Range is maximum at a 45-degree launch angle over level ground.

The velocity of one object measured from the frame of another moving object. It equals the vector difference of their velocities, so two bodies approaching each other close at the sum of their speeds.

Motion of a body along a circle at constant speed, where velocity direction changes continuously, producing a centripetal acceleration directed toward the centre. The acceleration magnitude equals speed squared divided by radius.

The net inward force that keeps a body moving in a circular path, equal to mass times speed squared divided by radius. It is provided by tension, friction, gravity, or other real forces, not a new kind of force.

The rotational analogue of linear momentum, equal to moment of inertia times angular velocity for a rigid body. It is conserved when no external torque acts on the system.

A measure of a body's resistance to change in its rotational motion, depending on mass distribution about the chosen axis. It plays the same role in rotation that mass plays in linear motion.

The turning effect of a force about an axis, equal to force times the perpendicular distance from the axis to the line of action. It changes a body's angular momentum and is measured in newton metres.

Oscillation in which acceleration is directly proportional to displacement from equilibrium and directed oppositely to it. Its period is independent of amplitude, and displacement follows a sine or cosine function of time.

A large-amplitude response occurring when a system is driven at a frequency close to its natural frequency. It explains increased sound from tuned instruments and the collapse of structures under matching vibration.

The apparent change in frequency of a wave when source and observer move relative to each other. Approaching motion raises observed frequency and receding motion lowers it, for both sound and light.

Complete reflection of light back into a denser medium when it strikes the boundary beyond the critical angle. It requires light travelling from denser to rarer medium and underlies optical fibres and mirages.

The angle of incidence in the denser medium for which the refracted ray grazes along the boundary, giving a refraction angle of 90 degrees. Beyond it, total internal reflection occurs.

The ratio of the speed of light in vacuum to its speed in a medium, or equivalently the sine of the incidence angle to the sine of the refraction angle. It measures how strongly a medium bends light.

Emission of electrons from a metal surface when light of sufficiently high frequency falls on it. It shows light behaves as particles, since electron energy depends on frequency, not intensity.

The minimum energy needed to remove an electron from the surface of a metal. In the photoelectric effect, incident photon energy minus work function equals the maximum kinetic energy of emitted electrons.

The wavelength associated with a moving particle, equal to Planck's constant divided by its momentum. It becomes significant only for very small masses such as electrons.

The time in which half the nuclei of a radioactive sample decay. After n half-lives, the fraction remaining is one divided by two raised to n; it is independent of the initial amount.

The amount of substance containing exactly Avogadro's number of elementary entities, about 6.022 times ten to the twenty-three. It links mass in grams to numbers of particles in chemistry calculations.

The number of moles of solute dissolved per litre of solution. It changes slightly with temperature because solution volume expands, unlike molality based on solvent mass.

The number of gram equivalents of solute per litre of solution, where equivalents depend on the reaction, such as protons donated or electrons transferred. It is used in titration and redox calculations.

The simplest whole-number ratio of atoms of each element in a compound, derived from percentage composition. The molecular formula is a whole-number multiple of it.

The mixing of atomic orbitals of similar energy to form new equivalent orbitals that determine molecular geometry. Common types are sp, sp2, and sp3, giving linear, trigonal planar, and tetrahedral shapes.

A model predicting molecular shape from the repulsion between electron pairs around a central atom, with lone pairs occupying more space than bonding pairs. It explains bent water and pyramidal ammonia geometries.

The number of electron pairs shared between two atoms, such as one for single and three for triple bonds. In molecular orbital theory it is half the difference between bonding and antibonding electrons.

When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts in the direction that partly opposes the change. It predicts product yield changes in reversible reactions.

The ratio of product concentrations to reactant concentrations, each raised to its stoichiometric coefficient, at equilibrium. Its value depends on temperature and indicates whether products or reactants dominate.

A solution that resists change in pH when small amounts of acid or base are added, usually containing a weak acid and its conjugate base. Its pH is described by the Henderson-Hasselbalch equation.

The property of an object that cannot be superimposed on its mirror image, as with a carbon bearing four different groups. Chiral molecules rotate plane-polarised light and exist as enantiomers.

A species that donates an electron pair to an electron-poor centre, attacking carbon in substitution reactions. Examples include hydroxide ion, ammonia, and the cyanide ion.

The value a function approaches as its input approaches a given point, whether or not the function equals that value there. Limits define continuity and underpin the derivative.

A property of a function whose value at a point equals its limit there, with no break or jump in its graph. Differentiability requires continuity, but continuity does not guarantee differentiability.

The instantaneous rate of change of a function with respect to its variable, equal to the limit of the difference quotient. Geometrically it gives the slope of the tangent to the curve.

The limit of a sum of areas of thin rectangles under a curve between two limits, giving a signed area. The fundamental theorem connects it to antiderivatives, allowing evaluation by substitution of limits.

A single number computed from a square matrix that indicates whether the matrix is invertible and gives the scale factor of the associated transformation. A zero determinant means the matrix has no inverse.

A matrix that, multiplied by the original square matrix, gives the identity matrix. It exists only when the determinant is non-zero and is used to solve systems of linear equations.

An arrangement of objects in which order matters, counted by n factorial divided by n minus r factorial when r objects are chosen from n. It differs from a combination, where order is irrelevant.

A selection of objects in which order does not matter, counted as n factorial divided by r factorial times n minus r factorial. It counts subsets rather than arrangements.

A function or table assigning probabilities to each possible value of a random variable, with all probabilities summing to one. It may be discrete, such as binomial, or continuous, such as normal.

The movement of water across a semipermeable membrane from a region of higher water potential to lower water potential. It drives water uptake by roots and maintains cell turgor.

Shrinkage of the protoplast away from the cell wall when a plant cell loses water in a hypertonic solution. It demonstrates the osmotic behaviour of the cell membrane and wall.

The outward pressure of cell contents against the cell wall when water enters by osmosis, keeping non-woody plants upright. Loss of turgor causes wilting.

Loss of water vapour mainly through stomata in leaves, creating the pull that draws water up the xylem. It is affected by humidity, temperature, wind, and light.

The process by which green plants use light energy to convert carbon dioxide and water into glucose and oxygen in chloroplasts. It occurs in light-dependent and light-independent reactions.

The light-driven splitting of water molecules in the light reactions of photosynthesis, releasing oxygen and providing electrons and protons. It occurs in the thylakoid membranes of chloroplasts.

Small pores in the leaf epidermis bounded by guard cells that open and close to regulate gas exchange and water loss. They admit carbon dioxide for photosynthesis and release oxygen and water vapour.

Cell division producing two genetically identical daughter cells with the same chromosome number as the parent. It supports growth, repair, and asexual reproduction.

Reduction division producing four haploid cells from one diploid cell through two successive divisions. It generates genetic variation and forms gametes in sexually reproducing organisms.

Exchange of segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis. It creates new allele combinations and increases genetic variation.

The tendency of genes located close together on the same chromosome to be inherited together rather than assorting independently. Recombination frequency between them reflects their distance.

Synthesis of an RNA molecule from a DNA template, catalysed by RNA polymerase. In eukaryotes it occurs in the nucleus and produces messenger RNA that carries the code to ribosomes.

The process in which ribosomes read messenger RNA codons and assemble the corresponding sequence of amino acids into a polypeptide. Transfer RNA delivers amino acids and matches codons by anticodons.

A sequence of three nucleotides in messenger RNA that specifies one amino acid or a stop signal. The genetic code is degenerate, with several codons coding for the same amino acid.

The process by which individuals with traits better suited to their environment survive and reproduce more, increasing those traits in later generations. It is a mechanism of evolution proposed by Darwin.

The formation of new and distinct species when populations become reproductively isolated and diverge over time. Isolation may be geographic, as with a physical barrier, or reproductive.