Assam Higher Secondary Physics key terms

The number of electric field lines crossing a surface, calculated as the field strength times the surface area times the cosine of the angle between field and normal. Measured in volt-metres.

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.

A vector quantity for a pair of equal and opposite charges, equal to charge times separation, pointing from negative to positive charge. Determines torque in an external field.

The ability of a conductor arrangement to store charge per unit potential difference, measured in farads. For parallel plates it grows with plate area and shrinks with separation.

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

The small average speed with which free electrons move along a conductor under an applied field, superimposed on their random thermal motion. 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. Higher mobility means easier conduction.

The current flowing per unit cross-sectional area of a conductor, a vector pointing along conventional current. Related to drift velocity through carrier number density and charge.

The resistance within a cell or source that causes its terminal voltage to fall below its electromotive force when current is drawn. It limits the maximum current a source can supply.

Two laws for circuits: 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-resistance network used to measure an unknown resistance. It is balanced when the ratio of resistances in one branch equals that in the other, giving zero galvanometer deflection.

A rule giving the magnetic field produced by a small current element: the field is proportional to current, element length and sine of angle, and falls as the inverse square of distance.

A statement that the line integral of magnetic field around any closed loop equals the permeability of free space times the net current threading the loop. Useful for symmetric current arrangements.

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

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 experiences torque in an external field.

The lagging of magnetic flux density behind the applied magnetising field in ferromagnetic materials, traced as a loop. The loop area represents energy lost per cycle as heat.

The property of a coil by which a changing current in it induces an opposing electromotive force in the same coil, measured in henries. Depends on geometry and core material.

The property by which a changing current in one coil induces an electromotive force in a nearby second coil, measured in henries. It depends on geometry, separation and relative orientation.

Circulating currents induced within the bulk of a conductor by a changing magnetic flux. They cause energy loss as heat and can be reduced by using laminated cores.

A device using mutual induction between two coils on a common core to change alternating voltage. An ideal one conserves power, so voltage ratio equals turns ratio.

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 circuit.

The total opposition to alternating current from resistance and reactance combined, measured in ohms. It determines current amplitude through the ratio of voltage amplitude to impedance.

The condition in a series circuit where inductive and capacitive reactances cancel, making impedance minimum and current maximum. It occurs at a frequency set by inductance and capacitance.

A fictitious current proportional to the rate of change of electric flux through a region, introduced so that Ampere's law holds for charging capacitors. It allows electromagnetic waves to propagate.

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

The complete reflection of light back into a denser medium when it strikes a boundary beyond the critical angle. It requires travel from denser to rarer medium.

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.

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

The minimum energy needed to remove an electron from the surface of a metal. It sets the threshold frequency below which no photoelectric emission occurs.

The reverse potential difference that just prevents the fastest photoelectrons from reaching the collector, making photocurrent zero. It measures the maximum kinetic energy of emitted electrons.

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

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

The total nuclear binding energy divided by the number of nucleons, indicating how tightly a nucleus is bound. It peaks near iron and explains fusion and fission energy release.

The time in which half the nuclei in a radioactive sample decay. It is constant for a given isotope and independent of sample size or chemical state.

The region near a p-n junction where mobile charge carriers have diffused away, leaving fixed ionised atoms and a built-in potential barrier. Its width changes with applied bias.

A heavily doped diode designed to operate safely in reverse breakdown, holding a nearly constant voltage. It is used for voltage regulation in circuits.

A circuit using diodes that converts alternating current into direct current, either half-wave or full-wave. A filter capacitor smooths the pulsating output.

An expression showing which base quantities and powers make up a derived physical quantity, written with symbols such as M, L and T. It checks equation consistency and converts units.

The digits in a measured value that carry meaning about its precision, including one estimated digit. Rules govern how they are kept through multiplication and addition.

The absolute error of a measurement divided by the measured value, often expressed as a percentage. It quantifies measurement accuracy independent of scale.

Two-dimensional motion of an object under gravity alone, with constant horizontal velocity and constant vertical acceleration. The path is a parabola when air resistance is ignored.

The velocity of one body as observed from another moving body, found by vector subtraction of the observer's velocity. It explains river-boat and rain-umbrella problems.

The acceleration of a body moving on a circular path, directed towards the centre and equal to speed squared divided by radius. It changes direction, not speed.

The product of a force and the time over which it acts, equal to the change in momentum produced. It is a vector quantity measured in newton-seconds.

The ratio of relative speed of separation to relative speed of approach for two colliding bodies. It equals one for elastic collisions and zero for perfectly inelastic ones.

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

The distance from the rotation axis at which the whole mass of a body could be concentrated to give the same moment of inertia. It measures mass distribution about an axis.

The minimum speed with which a body must be projected from a planet's surface to escape its gravitational pull forever, ignoring air resistance. It depends on planetary mass and radius.

The force per unit length acting along the surface of a liquid, tending to minimise surface area. It arises from unbalanced molecular attraction at the surface.

A measure of a fluid's internal friction, defined as the tangential stress per unit velocity gradient. It decreases with rising temperature in liquids.

The ratio of normal stress to the fractional change in volume of a material, describing resistance to compression. Its reciprocal is compressibility.

The ratio of heat removed from a cold reservoir to the work input in a refrigerator or heat pump. Higher values mean more efficient cooling.

Oscillation in which acceleration is directly proportional to displacement from equilibrium and directed towards it. Its displacement follows a sinusoidal function of time.

The progressive decrease in amplitude of an oscillation caused by dissipative forces such as friction or air resistance. Energy is lost to the surroundings as heat.

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

The apparent change in the observed frequency of a wave when the source, observer, or both move relative to the medium. Approach raises pitch; recession lowers it.