BSEB Inter Physics key terms

A vector equal to the product of one charge and the separation between two equal and opposite charges; it points from the negative to the positive charge and is measured in coulomb-metre.

The number of field lines crossing a surface, calculated as the surface integral of the electric field over that area; its SI unit is the newton metre squared per coulomb.

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

The ability of a conductor or capacitor to store charge per unit potential difference, given by charge divided by voltage and measured in farads.

The ratio of the permittivity of a material to that of free space, showing how much a medium reduces the electric field and increases a capacitor's capacitance.

The average velocity gained by free electrons along a conductor under an applied electric field, typically a fraction of a millimetre per second and linked to current by I = neAv.

The drift velocity acquired by a charge carrier per unit applied electric field; it measures how easily carriers move through a material and falls when scattering increases.

Current per unit cross-sectional area of a conductor, a vector quantity measured in amperes per square metre and related to field through conductivity.

An intrinsic property of a material giving the resistance of a conductor of unit length and unit area; it depends on material and temperature, not on shape.

The resistance within a cell or battery that causes its terminal voltage to fall below its electromotive force when current is drawn from it.

The work done by a source per unit charge in driving charge around a complete circuit, measured in volts; it equals the terminal potential difference only when no current flows.

Two circuit laws: the junction rule states that charge entering a node equals charge leaving, and the loop rule states that potential changes around any closed loop sum to zero.

A four-arm resistance network balanced when the ratio of resistances in adjacent arms is equal, giving zero galvanometer deflection and allowing an unknown resistance to be calculated.

An instrument that compares or measures potential differences by balancing them against a known potential drop along a uniform wire, drawing no current from the source being measured.

A law giving the magnetic field produced by a small current element as proportional to current, element length, and the sine of the angle, divided by 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 total current passing through the loop.

The total force on a moving charge in electric and magnetic fields, combining the electric force with the magnetic force qv cross B, which acts perpendicular to velocity.

A particle accelerator in which a magnetic field bends charged particles into spiral paths while an alternating voltage repeatedly accelerates them across a gap between two hollow electrodes.

A long coil of insulated wire that produces a nearly uniform magnetic field inside when carrying current, behaving like a bar magnet with north and south ends.

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

The lag of magnetic flux density behind the magnetising field when a ferromagnetic material is cycled, producing a loop whose area represents energy lost as heat per cycle.

The property of a coil by which a changing current in it induces an opposing electromotive force; it equals flux linkage per unit current and is measured in henries.

The property of two neighbouring coils whereby a changing current in one induces an electromotive force in the other, equal to flux linkage in the second per unit current in the first.

Circulating currents induced within the body of a conductor by a changing magnetic flux, which dissipate energy as heat and are reduced by using laminated cores.

The total opposition a circuit offers to alternating current, combining resistance and reactance as a complex quantity and measured in ohms.

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

The cosine of the phase angle between voltage and current in an alternating circuit; it equals one for a purely resistive circuit and zero for a purely reactive one.

A device that changes alternating voltage using two coils sharing a magnetic core, with the voltage ratio equal to the turns ratio and no change in frequency.

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

The angle of incidence in the denser medium for which the refracted ray grazes the boundary at ninety degrees; beyond it total internal reflection occurs.

The ratio of the speed of light in vacuum to its speed in a medium, also equal to the sine of the incidence angle divided by the sine of the refraction angle.

The superposition of two coherent waves producing regions of reinforced and cancelled intensity; sustained fringes require sources with a constant phase difference.

The spreading of waves around obstacles and through apertures, producing alternating bright and dark bands whose spacing depends on wavelength and slit width.

The restriction of light vibrations to a single plane, demonstrating the transverse nature of light and achievable by reflection, scattering, or passage through certain crystals.

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

The emission of electrons from a metal surface when light above a threshold frequency strikes it, with maximum kinetic energy depending on frequency rather than intensity.

The minimum energy needed to remove an electron from the surface of a metal, related to the threshold frequency by the Planck relation.

The wavelength associated with a moving particle, equal to Planck's constant divided by its momentum, explaining electron diffraction and quantised atomic orbits.

The time in which half the nuclei in a radioactive sample decay; it is constant for a given isotope and related to the decay constant by a natural logarithm of two.

The difference between the mass of a nucleus and the sum of the masses of its separated nucleons, appearing as binding energy according to the mass-energy relation.

The statement that the rate of decay of a sample is proportional to the number of undecayed nuclei present, giving an exponential decrease with time.

The narrow zone around a p-n junction depleted of mobile charge carriers, containing fixed ions and creating a potential barrier across the junction.

A heavily doped diode designed to operate safely in reverse breakdown, where the voltage stays nearly constant, making it useful as a voltage regulator.

A circuit using diodes that converts alternating current into direct current, either half-wave with one diode or full-wave with a centre-tapped or bridge arrangement.

The smallest measurement an instrument can read directly, found by dividing the value of one main-scale division by the number of divisions on the vernier or circular scale.

A systematic instrument error present when the zero marks do not coincide with the reading at true zero; it is corrected by adding or subtracting the measured deviation.

A measuring instrument with a main scale and a sliding vernier scale that allows lengths and internal or external diameters to be read to a fraction of a millimetre.

A technique using the base dimensions of physical quantities to check equation consistency, convert units, and derive relationships up to a dimensionless constant.

The digits in a measurement that carry meaningful information about its precision, used to round results so they do not overstate accuracy.

The ratio of the absolute error in a measurement to the measured value, often expressed as a percentage and combined when quantities are multiplied or divided.

The process of varying a property of a high-frequency carrier wave, such as amplitude or frequency, to carry a lower-frequency information signal.

The range of frequencies occupied by a signal or that a communication channel can carry; wider bandwidth allows higher data rates but needs more spectrum.

A conductor or array that radiates or receives electromagnetic waves, ideally with length comparable to a quarter or half wavelength for efficient transmission.

The minimum speed needed for a body to leave a planet's gravitational field without further propulsion, equal to the square root of twice the gravitational parameter divided by radius.

Three empirical laws of planetary motion: orbits are ellipses with the Sun at a focus, equal areas are swept in equal times, and the period squared is proportional to the semimajor axis cubed.