RBSE SS Physics key terms

The number of field lines passing through a surface, calculated as the field strength times the area times the cosine of the angle between the field and the surface normal. 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. It simplifies field calculations for symmetric charge distributions.

A vector pointing from a negative charge to a positive charge, with magnitude equal to charge times separation. It measures the polarity of a pair of equal and opposite charges.

The ratio of charge stored on a conductor to the potential difference across it, measured in farads. It depends only on the geometry and the medium between the plates.

The ratio of the permittivity of a medium to that of free space, also called relative permittivity. It shows how much a material reduces the electric field inside a capacitor.

The small average velocity with which free electrons move along a conductor under an applied electric field, typically around a fraction of a millimetre per second. It is proportional to the field.

The drift velocity acquired by a charge carrier per unit applied electric field, measured in square metres per volt-second. It indicates how easily carriers move through a material.

The current flowing per unit cross-sectional area, a vector quantity measured in amperes per square metre. It equals conductivity times the electric field in a conductor.

The resistance within a source such as a cell that opposes current flow through it, causing its terminal voltage to fall below its electromotive force when delivering current.

The work done by a source in driving unit charge around a complete circuit, measured in volts. It is the maximum potential difference a source can provide 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 vector for a current loop with magnitude equal to current times loop area, directed along the axis by the right-hand rule. It measures the torque a loop experiences in a magnetic field.

A relation 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 net current enclosed by that loop.

The lag of magnetic flux density behind the magnetising field in a ferromagnetic material as the field 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, defined as the flux linkage per unit current and measured in henries.

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

Circulating currents induced within the body of a bulk conductor by a changing magnetic flux, which dissipate energy as heat unless reduced by laminations.

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

The cosine of the phase angle between voltage and current in an alternating circuit, equal to true power divided by apparent power. It equals one for a purely resistive load.

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

A device with two coupled coils on a common core that changes alternating voltage levels, with the secondary-to-primary voltage ratio equal to the turns ratio for an ideal device.

A fictitious current proportional to the rate of change of electric flux through a region, introduced so that Ampere's law holds during capacitor charging and which generates a magnetic field.

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.

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

The complete return of light into a denser medium when it strikes a boundary with a rarer medium at an angle exceeding the critical angle, with no refracted ray.

The angle of incidence in a denser medium for which the refracted ray grazes the boundary, so that beyond it total internal reflection occurs.

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

The superposition of two or more coherent waves producing regions of reinforced and cancelled intensity, giving alternate bright and dark fringes in a stable pattern.

The property of two waves having a constant phase difference over time, which is necessary for a stable interference pattern to be observed.

The bending and spreading of waves around obstacles or through narrow openings, producing a pattern of fringes whose width depends on wavelength and slit size.

The minimum energy required to remove an electron from the surface of a metal, characteristic of the material and usually expressed in electronvolts.

The lowest frequency of incident light that can eject photoelectrons from a given metal surface, below which no emission occurs regardless of intensity.

The reverse potential difference needed to stop the fastest photoelectrons from reaching the collector, giving a direct measure of their maximum kinetic energy.

The time in which half of the radioactive nuclei in a sample decay, a constant characteristic of each radionuclide and independent of sample size.

The probability per unit time that a given nucleus will decay, equal to the natural logarithm of two divided by the half-life.

The difference between the sum of the masses of the nucleons in a nucleus and the actual nuclear mass, appearing as binding energy according to mass-energy equivalence.

The narrow zone around a p-n junction where mobile charge carriers have diffused away, leaving fixed ions and creating an internal electric field and potential barrier.

A heavily doped diode designed to operate in reverse breakdown, where voltage stays nearly constant over a range of currents, making it useful for voltage regulation.

A circuit using diodes that converts alternating current into unidirectional current, either half-wave or full-wave, exploiting one-way conduction across a junction.

The smallest measurement an instrument can read directly, such as the value of one division on a vernier scale, which limits the precision of readings.

A systematic fault in an instrument where it does not read zero when the measured quantity is zero, corrected by adding or subtracting the recorded offset.

The absolute error in a measurement expressed as a percentage of the measured value, used to compare the precision of results of different magnitudes.

A technique that checks equations and derives relations by comparing the powers of base units on both sides, exploiting the principle that physical quantities have consistent dimensions.

The digits in a measured value that carry meaning about its precision, including all certain digits plus one estimated digit, which govern rounding in calculations.

The ratio of the amplitude change of a carrier wave to its unmodulated amplitude, indicating the depth of amplitude modulation and lying between zero and one for no distortion.

The range of frequencies occupied by a signal or required by a communication channel, determined by the highest modulating frequency and the type of modulation used.

Transmission of radio waves by reflection from the ionosphere, allowing long-distance communication at certain frequencies, especially at night.