UPMSP Intermediate Physics - Code 151 key terms

The number of electric field lines passing through a surface, calculated as the field strength multiplied by 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. 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 charge pair and determines torque in an external field.

The ability of a conductor system to store charge per unit potential difference, measured in farads. For a parallel-plate capacitor it equals permittivity times area divided by plate separation.

The ratio of a medium's permittivity to that of free space, showing how much a material reduces the electric field between capacitor plates. It is dimensionless and greater than one for insulators.

The small average speed at which free electrons move along a conductor under an applied electric field, typically a fraction of a millimetre per second. It links current to electron density and cross-sectional area.

The drift velocity acquired by a charge carrier per unit applied electric field, measured in square metres per volt-second. Higher mobility means carriers respond more readily to a field.

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

The opposition to current flow inside a cell or battery itself, caused by its electrolyte and electrodes. It reduces terminal voltage below the electromotive force whenever current is drawn.

The voltage actually available across the external terminals of a cell while it delivers current. It equals electromotive force minus the drop across internal resistance during discharge.

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-resistance network used to measure an unknown resistance by balancing two potential dividers. At balance, the galvanometer shows zero deflection and resistance ratios are equal.

A uniform resistance wire with a sliding contact that compares or measures electromotive forces without drawing current from the cell under test. Balance length is proportional to the unknown emf.

A relation giving the magnetic field produced by a small current element: field is proportional to current times element length times sine of angle, divided by distance squared. It is the magnetic analogue of Coulomb's law.

A statement that the line integral of magnetic field around a closed path equals the permeability of free space times the total current enclosed by that path. It gives quick results for symmetric current arrangements.

The total force on a moving charge in electric and magnetic fields, combining the electric force with the magnetic force perpendicular to both velocity and field. It explains circular motion of charges in magnetic fields.

A long coil of insulated wire that produces an almost uniform magnetic field along its axis when carrying current. Field strength equals permeability times turns per unit length times current.

The turning effect experienced by a current-carrying coil placed in a magnetic field, proportional to current, area, field strength and sine of the angle between field and normal. It is the basis of moving-coil instruments.

A particle accelerator in which a magnetic field bends charged particles into spiral paths while an alternating voltage repeatedly boosts their energy. Its frequency is fixed by charge, field and particle mass.

The number of magnetic field lines crossing a surface, equal to field strength times area times cosine of the angle between field and surface normal. It is measured in webers.

A statement that the induced electromotive force in a circuit equals the negative rate of change of magnetic flux through it. It underpins generators, transformers and induction heating.

A rule stating that induced current flows in a direction that opposes the change in flux producing it. It is a direct consequence of energy conservation in electromagnetic induction.

The property of a coil by which a changing current in it induces an opposing emf in the same coil. It equals flux linkage per unit current and is measured in henries.

The total opposition offered by an AC circuit to current flow, combining resistance and reactance. It equals the peak voltage divided by peak current and is measured in ohms.

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

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

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

The angle of incidence in the denser medium for which the refracted ray grazes the boundary between two media. Beyond it, total internal reflection occurs instead of refraction.

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

The superposition of two coherent light waves producing alternate bright and dark bands, where amplitudes add or cancel. Fringe spacing depends on wavelength, screen distance and slit separation.

The spreading of light around obstacles and through narrow openings, producing alternate maxima and minima. In a single slit the central maximum is the brightest and widest.

Two light sources that maintain a constant phase difference and equal frequency, so their waves produce a stable interference pattern. Independent lamps are not coherent.

The emission of electrons from a metal surface when light of sufficiently high frequency falls on it. It demonstrates the particle nature of light and depends on frequency, not intensity, for electron energy.

The minimum energy needed to remove an electron from the surface of a metal, usually expressed in electron-volts. It fixes the threshold frequency for photoemission.

The lowest frequency of incident light that can eject electrons from a given metal surface, regardless of intensity. Below it, no photoemission occurs however bright the light.

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

The energy released when nucleons combine to form a nucleus, equivalent to the mass defect times the square of the speed of light. It measures nuclear stability.

The time in which half the nuclei of a radioactive sample decay. It is independent of sample size and temperature and links decay constant to activity.

A pure semiconductor with no added impurity, where conduction arises from equal numbers of thermally generated electrons and holes. Its conductivity rises with temperature.

The deliberate addition of small amounts of impurity atoms to a semiconductor to increase its conductivity and create n-type or p-type material. Dopant concentration controls carrier type and number.

The boundary formed when p-type and n-type semiconductor regions meet, creating a depletion layer and a built-in potential barrier. It conducts easily in one direction only.

A heavily doped diode designed to operate safely in reverse breakdown, maintaining a nearly constant voltage across it. It is used for voltage regulation and reference.

A circuit using diodes that converts alternating current into pulsating direct current. A full-wave version uses both halves of the AC cycle, giving higher output.

The smallest measurement a given instrument can read reliably, such as 0.01 mm for a vernier calliper. It determines the precision of an experimental result.

A systematic fault in an instrument where it does not read zero when measuring nothing, due to manufacturing or wear. It must be added or subtracted from all readings.

A reading mistake caused by viewing a scale or pointer from an angle rather than straight on. It is avoided by keeping the eye level with the pointer.

An expression showing which base quantities and powers make up a derived quantity, such as force as mass times length per square time. It checks equation consistency and converts units.

Scalars have magnitude only, such as mass and temperature; vectors have magnitude and direction, such as displacement and force. Vectors obey special addition rules.

The process of splitting a vector into perpendicular components along chosen axes, usually horizontal and vertical. Components recombine by vector addition to restore the original vector.

The process of varying a property of a high-frequency carrier wave, such as amplitude or frequency, in step with a message signal. It allows efficient transmission of information.

The range of frequencies occupied by a signal or required by a communication channel. Higher bandwidth permits more information to be carried per unit time.

Transmission of radio waves by reflecting them from the ionosphere back to the ground, useful for long distances. It works best for frequencies up to about 30 megahertz.