Karnataka II PUC Physics (KSEAB) key terms

The number of electric field lines crossing a surface, calculated as the field strength times the area projected perpendicular to the field. Its SI unit is the volt metre.

A statement that the total electric flux through any closed surface equals the enclosed charge divided by the permittivity of free space, regardless of the surface's shape or size.

A vector quantity for a pair of equal and opposite charges, equal to charge times separation, pointing from the negative charge to the positive charge. Its SI unit is the coulomb metre.

A constant describing how readily a vacuum permits electric field lines, equal to about 8.85 × 10⁻¹² farad per metre. It appears in Coulomb's law and in Gauss's law.

The turning effect on an electric dipole placed in a uniform field, equal to the cross product of dipole moment and field. It is maximum when the dipole lies perpendicular to the field.

The ability of a conductor or capacitor system to store charge per unit potential difference, defined as charge divided by voltage. Its SI unit is the farad.

The ratio of a medium's permittivity to that of free space, showing how much a dielectric reduces the field between capacitor plates and multiplies capacitance. It is dimensionless and always at least one.

The work done in charging a capacitor, held in its electric field. It equals half the product of capacitance and the square of the voltage across the plates.

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

The drift velocity acquired by a charge carrier per unit applied electric field, indicating how easily carriers move through a material. Its SI unit is square metre per volt second.

An intrinsic property of a material measuring its opposition to current flow, equal to resistance times cross-sectional area divided by length. Its SI unit is the ohm metre.

The current per unit cross-sectional area flowing through a conductor, treated as a vector along the current direction. Its SI unit is the ampere per square metre.

The fractional change in resistance of a material per degree change in temperature. It is positive for metals and negative for semiconductors and electrolytes.

A conservation-of-charge statement that the algebraic sum of currents meeting at a circuit junction is zero, so total current entering equals total current leaving.

A conservation-of-energy statement that the algebraic sum of potential differences around any closed circuit loop is zero, used to analyse multi-loop circuits.

A four-resistance network used to measure an unknown resistance, balanced when the ratio of resistances in adjacent arms is equal and no current flows through the galvanometer.

A device that compares or measures potential differences without drawing current, by balancing an unknown emf against the potential drop along a uniform wire carrying a steady current.

A relation giving the magnetic field produced by a small current element at a point, proportional to current and length 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 loop.

The total force on a moving charge in combined electric and magnetic fields, equal to the electric force plus the magnetic force, which acts perpendicular to both velocity and field.

A particle accelerator in which a magnetic field bends particles into circular paths while an alternating voltage repeatedly boosts their energy, limited by relativistic mass increase.

The turning effect on a current-carrying coil in a magnetic field, equal to the cross product of the magnetic moment and the field, forming the basis of moving-coil instruments.

A coil of wire wound in closely spaced turns, producing a nearly uniform magnetic field along its axis when carrying current, behaving like a bar magnet.

The lagging of magnetic flux density behind the magnetising field in a ferromagnetic material over a magnetisation cycle, causing energy loss as heat in alternating-field applications.

The residual magnetic flux density remaining in a ferromagnetic material when the magnetising field is reduced to zero, indicating how well it retains magnetisation.

The reverse magnetic field strength needed to bring the flux density of a magnetised material back to zero, measuring how hard it is to demagnetise it.

Circulating induced currents set up in the body of a conductor by a changing magnetic flux, causing energy loss as heat and used deliberately in induction braking and heating.

The property of a coil by which it opposes any change in current through itself, defined as flux linkage per unit current. Its SI unit is the henry.

The property by which a changing current in one coil induces an emf in a neighbouring coil, defined as flux linkage in the second coil per unit current in the first.

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

The total opposition offered by an alternating-current circuit containing resistance, inductance and capacitance, combining resistance with net reactance. Its SI unit is the ohm.

The condition in a series circuit where inductive and capacitive reactances cancel, making impedance minimum and current maximum at a particular resonant frequency.

A fictitious current associated with a changing electric field between capacitor plates, added to conduction current by Maxwell so that Ampere's law holds across a charging capacitor.

A self-sustaining oscillation of electric and magnetic fields perpendicular to each other and to the direction of travel, propagating through vacuum at the speed of light.

The complete reflection of light back into a denser medium when it strikes the boundary with a rarer medium at an angle exceeding the critical angle.

The angle of incidence in a denser medium for which the refracted ray grazes the boundary with a rarer medium, marking the onset of total internal reflection.

A thin flexible strand of glass or plastic that guides light along its length by repeated total internal reflection at the core–cladding boundary, used in communication and endoscopy.

The modification of intensity produced where two coherent waves superpose, giving alternate bright and dark fringes from constructive and destructive combination.

Two light sources emitting waves of the same frequency with a constant phase difference, a requirement for producing a stable interference pattern.

The bending and spreading of waves around obstacles or through narrow openings, producing a pattern of fringes whose width increases with wavelength.

The minimum energy needed to release an electron from the surface of a metal, characteristic of the material and usually expressed in electron volts.

The lowest frequency of incident light that can eject electrons from a given metal surface, below which no photoelectric emission occurs however intense the light.

The emission of electrons from a metal surface when light of sufficient frequency falls on it, explained by light behaving as discrete packets of energy.

The wavelength associated with a moving particle, equal to Planck's constant divided by its momentum, showing wave behaviour on the atomic scale.

The difference between the mass of a stable nucleus and the sum of the masses of its individual protons and neutrons, appearing as binding energy.

The total energy holding a nucleus together divided by its nucleon count, a measure of nuclear stability that peaks near iron and falls for very light or heavy nuclei.

A relation stating that the rate of decay of radioactive nuclei is proportional to the number present, giving exponential decrease with time characterised by a half-life.

A narrow region at a p-n junction, free of mobile charge carriers and containing fixed ions, that creates the built-in potential barrier across the junction.

A heavily doped p-n junction designed to operate safely in reverse breakdown, holding a nearly constant voltage that makes it useful for voltage regulation.

A circuit, usually using one or more diodes, that converts alternating current into unidirectional current, either half-wave or full-wave.

A statement that the current through a metallic conductor is directly proportional to the potential difference across it at constant temperature, the constant being resistance.

The distance between the pole of a spherical mirror or the optical centre of a lens and its principal focus, half the radius of curvature for a mirror.

A dimensionless measure of how strongly a material becomes magnetised in response to an applied magnetic field, small and positive for paramagnets and negative for diamagnets.

A sensitive instrument that detects small currents by the deflection of a coil in a magnetic field, convertible into an ammeter with a shunt or a voltmeter with a series resistor.