La Rioja PAU Physics key terms

The ratio of the speed of light in a vacuum to the speed of light in a medium, For light incident from vacuum or approximately air, it also equals sin(incidence)/sin(refraction); for two general media that ratio is their relative refractive index.

The angle of incidence in the denser medium for which the angle of refraction in the less dense medium is exactly ninety degrees. Beyond it total internal reflection occurs.

The complete reflection of light back into a denser medium when it strikes the boundary at an angle of incidence greater than the critical angle. It is used in optical fibres.

The spreading of waves as they pass through an aperture or around an obstacle, becoming more pronounced when the wavelength is comparable to the gap or obstacle size.

The superposition of two or more waves to produce regions of reinforced and cancelled displacement. Constructive interference gives maxima; destructive interference gives minima.

Two wave sources that maintain a constant phase difference and have the same frequency, so that a stable interference pattern can be observed. Lasers provide a common example.

A wave pattern formed when two waves of equal frequency and amplitude travel in opposite directions, producing fixed nodes and antinodes. Energy is not transported along the medium.

The large-amplitude oscillation that occurs when a system is driven at a frequency matching one of its natural frequencies. It is used in tuning circuits and musical instruments.

The charge stored per unit potential difference across a capacitor, measured in farads. For a parallel-plate capacitor it equals permittivity times area divided by plate separation.

For a capacitor-resistor circuit, the product of resistance and capacitance; it is the time for the charge to fall to about thirty-seven per cent of its initial value during discharge.

The force per unit positive charge experienced at a point in an electric field, measured in newtons per coulomb. It is a vector quantity with direction along the field line.

The energy transferred per unit charge when charge moves between two points in a circuit, measured in volts. It is the work done per coulomb.

The energy supplied by a source per unit charge driven around a complete circuit, measured in volts. It differs from terminal potential difference when internal resistance is present.

The resistance within a source of electromotive force that causes the terminal potential difference to fall as the current drawn increases. It dissipates energy as heat inside the source.

The generation of an electromotive force in a conductor when the magnetic flux linking it changes. The induced emf is proportional to the rate of change of flux linkage.

The product of the magnetic flux density and the area perpendicular to it, measured in webers. Flux linkage multiplies this by the number of turns in a coil.

The direction of an induced current is such that it opposes the change producing it. This is a consequence of conservation of energy and gives the negative sign in Faraday's law.

The minimum energy needed to remove an electron from the surface of a metal. It is a property of the metal and appears in the photoelectric equation.

The emission of electrons from a metal surface when light of frequency above a threshold falls on it. It demonstrates the particle nature of light.

The lowest frequency of incident radiation that can just cause photoelectric emission from a given metal surface. Below it, the ordinary weak-illumination single-photon model predicts no emitted photoelectrons.

The time taken for half the nuclei in a given radioactive sample to decay, or for the activity to fall to half its initial value. It is constant for a given isotope.

The probability per unit time that an individual nucleus will decay. It is related to half-life by the expression lambda equals natural log of two divided by half-life.

The number of nuclear disintegrations occurring per second in a radioactive sample, measured in becquerels. It decreases exponentially with time according to the decay constant.

The difference between the total mass of the separate nucleons in a nucleus and the mass of the assembled nucleus. It appears as binding energy according to mass-energy equivalence.

The energy required to separate a nucleus completely into its individual protons and neutrons. It equals the mass defect multiplied by the square of the speed of light.

A consistent deviation of measurements from the true value in one direction, caused by faulty apparatus or flawed method. It affects accuracy but not necessarily precision.

Unpredictable variation in measurements about a mean value, caused by fluctuating conditions or limited resolution. It reduces precision and can be lessened by averaging repeated readings.

How close a measured value is to the accepted true value. It is affected mainly by systematic error, whereas precision concerns the spread of repeated readings.

The degree of agreement among repeated measurements of the same quantity, reflected in a small spread of values. It is affected by random error and instrument resolution.

A force directed toward equilibrium, often proportional to displacement over an explicitly specified linear range; its direction determines the sign in the oscillator equation.