Kerala Plus Two Physics (DHSE) key terms

The measure of the number of electric field lines crossing a surface, calculated as the field strength multiplied by the surface area and the cosine of the angle between the field and the surface normal.

A statement that the total electric flux through any closed surface equals the net charge enclosed divided by the permittivity of free space, useful for finding fields in symmetric charge distributions.

A vector quantity for a pair of equal and opposite charges, equal to charge times the separation distance, pointing from the negative charge toward the positive charge; it sets the torque in an external field.

The ratio of the charge stored on a conductor to the potential difference across it, measured in farads; for a parallel plate capacitor it depends on plate area, separation and the medium between the plates.

The ratio of the permittivity of a medium to that of free space, showing how much a material reduces the electric field between capacitor plates and thereby multiplies the capacitance.

The small average velocity with which free electrons move along a conductor under an applied electric field, superimposed on their random thermal motion; it is typically of the order of a fraction of a millimetre per second.

The drift velocity per unit applied electric field for a charge carrier in a material, expressed in square metres per volt-second; it measures how easily carriers move and is larger for electrons than for holes in silicon.

The electric current per unit cross-sectional area of a conductor, a vector quantity measured in amperes per square metre and related to drift velocity by the carrier number density and charge.

The resistance within a source of electromotive force that causes its terminal voltage to fall below the emf when current is drawn, and to rise above it while being charged.

The voltage actually available across the external circuit connected to a cell or battery, equal to the emf minus the product of current and internal resistance during discharge.

Two conservation statements used to analyse circuits: the junction rule says charge entering a node equals charge leaving, and the loop rule says the sum of potential changes around any closed loop is zero.

A vector for a current loop or magnet equal to current times loop area, directed along the axis by the right-hand rule; it determines the torque experienced in an external magnetic field.

A relation giving the magnetic field produced at a point by a small current element as proportional to current, element length, sine of the angle and inversely proportional to the square of the distance.

A statement that the line integral of magnetic field around a closed loop equals the permeability of free space times the net current passing through the surface bounded by the loop.

The turning effect on a current-carrying coil in a magnetic field, equal to the cross product of its magnetic dipole moment and the field; it is the basis of the moving-coil galvanometer.

The property of a coil by which a changing current in it induces an emf opposing that change, measured in henries as the flux linkage produced per unit current.

The property of two nearby coils whereby a changing current in one induces an emf in the other, defined as the flux linkage in the second coil per unit current in the first.

A rule stating that an induced current always flows in a direction whose magnetic effect opposes the change in flux that produced it, a direct consequence of energy conservation.

The total opposition offered by a series AC circuit containing resistance, inductance and capacitance, equal to the peak voltage divided by peak current and measured in ohms.

The condition in a series AC circuit where inductive and capacitive reactances cancel, making impedance minimum and current maximum; it occurs at an angular frequency equal to one over the square root of inductance times capacitance.

The cosine of the phase angle between voltage and current in an AC circuit, equal to true power divided by apparent power; it is one for a pure resistor and zero for a pure inductor or capacitor.

A current introduced by Maxwell equal to the rate of change of electric flux through a region, which produces a magnetic field just as a conduction current does and completes the circuit between capacitor plates.

A self-propagating oscillation of electric and magnetic fields perpendicular to each other and to the direction of travel, moving in vacuum at the speed of light and carrying energy and momentum.

A vector equal to the cross product of electric field and magnetic field divided by permeability, giving the rate of energy flow per unit area for an electromagnetic wave.

The complete return of light into a denser medium when it strikes the boundary with a rarer medium at an angle exceeding the critical angle, occurring because refraction is impossible beyond that angle.

The angle of incidence in the denser medium for which the refracted ray grazes the boundary between two media, equal to the inverse sine of the ratio of the two refractive indices.

A measure of the light-gathering capacity of an optical fibre, equal to the sine of the maximum acceptance angle and dependent on the refractive indices of core and cladding.

The minimum frequency of incident light below which no photoelectrons are emitted from a given metal surface, regardless of intensity, because photon energy is then less than the work function.

The minimum energy needed to remove an electron from the surface of a metal, usually expressed in electronvolts and equal to Planck's constant times the threshold frequency.

The retarding potential difference applied to stop the fastest photoelectrons in a photocell, whose value multiplied by electronic charge equals the maximum kinetic energy of emission.

The wavelength associated with a moving particle, equal to Planck's constant divided by its momentum; it explains why electrons show diffraction and interference in crystal lattices.

The radius of the lowest-energy electron orbit in the hydrogen atom, about 0.53 angstrom, obtained from quantised angular momentum and used as the unit for other allowed orbit radii.

The difference between the total mass of the nucleons in a nucleus and the actual measured nuclear mass, which appears as binding energy according to Einstein's mass-energy relation.

The time in which half the nuclei in a radioactive sample decay, a constant characteristic of each radionuclide and related to the decay constant by the natural logarithm of two divided by lambda.

The narrow zone around a p-n junction where mobile charge carriers have diffused away, leaving fixed ionised dopant atoms that create an internal electric field and a potential barrier.

A reverse-breakdown mechanism in heavily doped diodes where a strong junction field pulls electrons directly from covalent bonds, giving a sharp, stable and reversible breakdown voltage used for voltage regulation.

The conversion of alternating current into direct current using diodes that conduct in one direction only, either a half-wave circuit or a full-wave bridge arrangement.

An expression showing which base quantities and powers make up a derived quantity, such as force being mass times length divided by the square of time; it checks equation consistency.

The digits in a measurement that carry meaningful information about its precision, starting from the first non-zero digit; the result of a calculation must keep the least number among the inputs.

A reading error caused by viewing a scale from an angle rather than straight on, so the pointer appears displaced against the scale; avoided by keeping the eye level with the pointer.

The ratio of the limiting maximum static friction force to the normal reaction between two surfaces at rest relative to each other, a dimensionless number depending on the pair of materials.

The acceleration of a body moving on a circular path, directed toward the centre and equal to the square of the speed divided by the radius of the path.

The product of a force and the short time over which it acts, equal to the change in momentum of the body; it explains why a longer contact time reduces the average force.

The speed required for a satellite to stay in a circular orbit at a given height, equal to the square root of the gravitational parameter divided by the orbital radius.

The minimum speed with which a body must be projected from a planet's surface to escape its gravitational pull, about 11.2 kilometres per second for the Earth.

A statement that the square of a planet's orbital period is proportional to the cube of the semi-major axis of its orbit, with the same constant for all planets of a given central body.

The force per unit length acting along the surface of a liquid, arising from unbalanced cohesive forces, which makes drops spherical and supports small objects on water.

The internal resistance of a fluid to flow, measured by the tangential force per unit area needed to maintain unit velocity gradient between adjacent layers; it decreases on heating for liquids.

A statement that for steady streamlined flow of an ideal fluid, the sum of pressure, kinetic energy per unit volume and potential energy per unit volume remains constant along a streamline.

A statement of energy conservation for a system, saying that heat supplied to a system equals the change in its internal energy plus the work done by the system.

A change in a system in which no heat is exchanged with the surroundings, so work done on the gas raises its internal energy and temperature according to the relation pressure times volume to the power gamma is constant.

The ratio of heat extracted from a cold reservoir to the work supplied in a refrigerator; it equals the heat absorbed divided by the work input and is typically greater than one.

An oscillatory motion in which acceleration is directly proportional to displacement from equilibrium and directed oppositely, giving a sinusoidal displacement with a fixed period independent of amplitude.

The large-amplitude oscillation that occurs when a body is driven at its natural frequency, because energy is transferred most efficiently from the driving source to the oscillator.

The periodic variation in loudness heard when two sound waves of slightly different frequencies superpose, with the beat frequency equal to the difference between the two frequencies.