CHSE Odisha Elective Physics key terms

The number of electric field lines passing through a given surface area, calculated as the field strength times the perpendicular area. It measures how much field penetrates a surface and underpins Gauss's law.

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 pair of equal and opposite charges separated by a small distance. It is characterised by a dipole moment equal to charge times separation, and it experiences torque in a uniform field.

The ability of a conductor or system to store charge per unit potential difference, measured in farads. It depends on geometry and the medium between the plates, not on the charge stored.

The ratio of the permittivity of a material to that of free space, showing how much a medium reduces the electric field between capacitor plates. Also called relative permittivity.

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 a fraction of a millimetre per second.

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.

An intrinsic property of a material giving the resistance of a unit length with unit cross-sectional area. It depends on temperature and material, unlike resistance which also depends on shape.

The resistance within a cell or battery that causes its terminal voltage to fall below its electromotive force when current flows. It converts some chemical energy into heat inside the source.

The energy supplied by a source per unit charge driven around a complete circuit, measured in volts. Despite the name, it is not a force but a potential difference generated by the source.

Two conservation laws for circuits: the junction rule states currents into a node equal currents out, and the loop rule states potential changes around a closed loop sum to zero.

A relation giving the magnetic field produced at a point by a small element of current-carrying wire. The contribution is proportional to current, element length, and the sine of the angle.

A statement that the line integral of magnetic field around a closed loop equals the permeability of free space times the total current enclosed. It is the magnetic analogue of Gauss's law.

A vector describing the strength and orientation of a current loop or magnet as a source of magnetic field, equal to current times loop area. It determines torque experienced in an external field.

A long coil of insulated wire that produces a nearly uniform magnetic field inside when current flows. The field strength depends on turns per unit length and current.

The lagging of magnetic flux density behind the magnetising field in a ferromagnetic material as the field is cycled. The area of the loop represents energy lost as heat per cycle.

A rule stating that an induced current flows in a direction that opposes the change in magnetic flux producing it. It expresses conservation of energy in electromagnetic induction.

The total magnetic field passing perpendicularly through a given area, measured in webers. Changing this flux through a circuit is what induces an electromotive force.

The property of a coil by which a changing current in it induces an electromotive force opposing that change, measured in henries. It depends on coil geometry and core material.

The total opposition a circuit presents to alternating current, combining resistance and reactance, measured in ohms. It determines the amplitude of current for a given applied voltage.

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

A dimensionless measure of sharpness of resonance in a tuned circuit, equal to resonant frequency divided by bandwidth. Higher values give a narrower, more selective resonance peak.

The complete reflection of light back into a denser medium when it strikes a boundary with a rarer medium beyond the critical angle. It enables optical fibres and mirages.

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

The ratio of the speed of light in vacuum to its speed in a medium, indicating how strongly the medium bends light. It also relates to the ratio of sines of incidence and refraction angles.

The splitting of white light into its component colours because refractive index varies with wavelength. It causes rainbows and chromatic aberration in lenses.

The ability of an optical instrument to form distinct images of two closely spaced point objects. Larger apertures and shorter wavelengths improve it by reducing diffraction spreading.

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

The property of two waves having a constant phase difference over time, allowing them to produce a stable interference pattern. It requires matched frequency and a fixed phase relationship.

The bending and spreading of waves when they pass an obstacle or aperture, becoming pronounced when the obstacle size is comparable to the wavelength. It limits instrument resolution.

The emission of electrons from a metal surface when light of sufficient frequency falls on it. It demonstrates that light delivers energy in discrete quanta called photons.

The minimum energy required to remove an electron from the surface of a metal. Light below the corresponding threshold frequency cannot cause photoelectric emission, whatever its intensity.

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

The time in which half the nuclei in a radioactive sample decay. It is independent of the initial number of nuclei and characterises each radionuclide.

The energy required to separate all nucleons in a nucleus completely, equivalent to the mass defect times the square of the speed of light. It reflects nuclear stability per nucleon.

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

A zone near a p-n junction depleted of mobile charge carriers, leaving fixed ionised dopant atoms that create a built-in potential barrier. It widens under reverse bias.

Applying a voltage that makes the p-side of a junction positive relative to the n-side, narrowing the depletion region and allowing substantial current to flow.

A circuit using diodes that converts alternating current into pulsating direct current by allowing current in only one direction. A full-wave version uses both half-cycles.

A measure of a body's resistance to change in rotational motion, equal to the sum of mass times the square of distance from the axis. It depends on the axis chosen.

The turning effect of a force about an axis, equal to force times the perpendicular distance from the axis. It changes angular momentum and causes angular acceleration.

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.

The minimum speed needed for a projectile to leave a planet's gravitational influence without further propulsion. It depends on planetary mass and radius but not on projectile mass.

The speed a satellite needs to maintain a stable circular orbit at a given radius, where gravitational attraction provides the centripetal force. It decreases with increasing orbital radius.

The ratio of tensile stress to tensile strain within the elastic limit, measuring a material's stiffness. A larger value means less extension for the same applied stress.

The greatest stress a material can bear and still return to its original shape when unloaded. Beyond it, permanent deformation occurs.

An oscillation in which acceleration is proportional to displacement from equilibrium and directed opposite to it. Its period is independent of amplitude for an ideal oscillator.

The progressive loss of oscillation amplitude caused by resistive forces that dissipate energy as heat. It eventually brings a freely oscillating system to rest.

The large-amplitude response of an oscillating system driven at its natural frequency. The amplitude peaks when driving frequency matches natural frequency and depends on damping.

The periodic variation in loudness heard when two sound waves of slightly different frequencies interfere. The beat frequency equals the difference between the two frequencies.

The apparent change in frequency of a wave when source and observer move relative to each other. Approach raises observed frequency and recession lowers it.

A pattern formed by two identical waves travelling in opposite directions, with fixed nodes and antinodes. It transfers no net energy and underpins vibration of strings and pipes.

The average distance a molecule travels between successive collisions with other molecules. It decreases as pressure or number density increases.

The number of independent ways a molecule can store energy, such as translation, rotation, or vibration. It determines the molar specific heat through the equipartition principle.

The square root of the average of the squared speeds of gas molecules. It rises with temperature and falls with increasing molar mass.

The smallest measurement an instrument can read directly, such as the value of one division on a vernier or screw gauge. It limits the precision of any reading taken.

A reading shown by an instrument when the true measurement is zero, caused by imperfect manufacture or wear. It must be added to or subtracted from all readings.

An apparent shift in the position of an object or scale mark when viewed from different angles. It is avoided by viewing perpendicular to the scale.