Canary PAU Physics key terms

Force per unit mass experienced by a small test mass placed at a point in a gravitational field; a vector pointing toward the attracting body, measured in N/kg and equal to the local free-fall acceleration.

Work done per unit mass by an external agent in bringing a small test mass from infinity to a point, taken as zero at infinity; a scalar measured in J/kg, always negative near a mass.

Minimum launch speed needed for a projectile to move from a body's surface to infinity without further propulsion, found by equating kinetic energy to the depth of the gravitational potential well.

Speed of a satellite in a circular orbit, set by the balance between gravitational attraction and centripetal acceleration; it decreases as the orbital radius increases, following the inverse square-root dependence on radius.

Circular equatorial orbit in which a satellite's period equals one sidereal day, so it appears fixed above one point on the surface; the radius is about 42,000 km from Earth's centre.

The square of a planet's orbital period is proportional to the cube of the semi-major axis of its orbit; for circular orbits the constant of proportionality depends only on the central mass.

Electric force per unit positive charge at a point, a vector measured in N/C or V/m; for a point charge it points radially outward for positive charge and inward for negative charge.

Work done per unit positive charge in bringing a small test charge from infinity to a point, taken as zero at infinity; a scalar in volts, positive near positive charge and negative near negative charge.

Surface integral of the electric field component perpendicular to a surface, measured in N·m²/C; it quantifies how much field passes through an area and underlies Gauss's law.

The total electric flux through any closed surface equals the enclosed charge divided by the permittivity of free space; useful for finding fields of highly symmetric charge distributions such as spheres and lines.

Surface on which every point has the same electric potential; no work is done moving charge along it, so field lines always cross it at right angles and it can represent a conductor's surface in equilibrium.

Ratio of the charge stored on one conductor of a capacitor to the potential difference between its plates, measured in farads; for parallel plates it increases with plate area and decreases with separation.

Insulating material placed between capacitor plates; its molecules polarise and partly cancel the internal field, raising capacitance by a relative permittivity factor and lowering the voltage for a given charge.

Vector quantity describing the strength and direction of a magnetic field, defined by the force on a current-carrying wire or moving charge; measured in tesla, equal to one N per A·m.

Total force on a charge moving through electric and magnetic fields, combining the electric force with the magnetic force perpendicular to both velocity and field; the magnetic part does no work.

Radius of the circular path followed by a charged particle moving perpendicular to a uniform magnetic field, obtained by equating magnetic force to centripetal force; it grows with momentum and shrinks with field strength.

Instrument that ionises a sample, accelerates the ions and separates them by mass-to-charge ratio using magnetic deflection, allowing identification of isotopes and unknown substances from their detected positions.

Product of magnetic flux density and the area perpendicular to it, measured in webers; it measures how many field lines pass through a loop and changes when the loop rotates or the field varies.

The induced electromotive force around a loop equals the negative rate of change of magnetic flux through it; faster flux changes or more turns give larger induced emf.

An induced current flows in the direction whose magnetic effect opposes the change in flux that produced it; this is the origin of the minus sign in Faraday's law and reflects energy conservation.

Property of a coil whereby a changing current in it induces a back emf opposing that change; defined as flux linkage per unit current and measured in henries.

Self-propagating oscillation of coupled electric and magnetic fields, perpendicular to each other and to the direction of travel; it needs no medium and travels at the speed of light in vacuum.

Restriction of a transverse wave's oscillations to one plane; for light it can be produced by reflection, by certain crystals, or by filters, and it demonstrates that light is a transverse wave.

The intensity transmitted through a polarising filter equals the incident intensity times the square of the cosine of the angle between the light's polarisation direction and the filter's transmission axis.

Oscillation in which acceleration is proportional to displacement from equilibrium and directed oppositely, giving a sinusoidal displacement-time graph with constant period independent of amplitude.

Large-amplitude oscillation that occurs when a driving frequency matches a system's natural frequency; the response peaks sharply and damping reduces both the peak height and its frequency.

Distance a wave crest travels per unit time, equal to frequency multiplied by wavelength; in a given medium it is set by the medium's properties and stays constant as frequency changes.

Pattern formed by two identical waves travelling in opposite directions, with fixed nodes and antinodes; only certain frequencies fit a given length, producing harmonics on strings and in pipes.

Change in observed frequency when source and observer move relative to each other; approaching motion raises the observed frequency and receding motion lowers it, for sound and for light alike.

Ratio of the speed of light in vacuum to its speed in a medium, always at least one; it determines how much a ray bends at an interface through Snell's law.

Angle of incidence in the denser medium for which the refracted ray grazes the interface at 90 degrees; beyond it total internal reflection occurs, and its sine equals the reciprocal of the refractive index.

Complete reflection of light back into the denser medium when incidence exceeds the critical angle; it requires travel from denser to less dense medium and enables optical fibres and prisms.

Plate with many closely spaced parallel slits that disperses light into sharp maxima at angles given by the grating equation; finer spacing gives wider separation of wavelengths and higher resolution.

Superposition of two or more waves producing regions of reinforced and cancelled displacement; sustained fringes require coherent sources with a constant phase difference and comparable wavelengths.

Property of waves having a constant phase relationship over time and space; lasers are highly coherent, which is why they produce stable interference and diffraction patterns over long path differences.

Slowing of a clock measured by an observer in relative motion; the dilated interval equals the proper interval multiplied by the Lorentz factor, an effect confirmed by muon lifetimes and atomic clocks.

Factor depending only on relative speed that scales time intervals, lengths and relativistic mass; it equals one at rest and grows without limit as speed approaches the speed of light.

Time interval measured by a clock at rest relative to the two events it separates, that is, at the same place in that frame; it is the shortest interval any inertial observer can record.

Energy a body possesses by virtue of its mass alone, given by mass times the square of the speed of light; it can be converted into other forms in nuclear and particle processes.

Increase in observed wavelength of light from a receding source, described by the Doppler effect for relative motion or by cosmic expansion for distant galaxies; it shifts spectral lines toward longer wavelengths.

Emission of electrons from a metal surface when illuminated above a threshold frequency; the maximum kinetic energy depends on frequency, not intensity, which supports the photon model of light.

Minimum energy needed to remove an electron from a metal surface; it equals the photon energy at the threshold frequency and appears as the intercept in the photoelectric stopping-potential graph.

Quantum of electromagnetic radiation carrying energy proportional to frequency and momentum equal to energy divided by the speed of light; its existence explains black-body spectra and the photoelectric effect.

Wavelength associated with a particle, equal to Planck's constant divided by its momentum; it becomes measurable for electrons and is demonstrated by electron diffraction through crystals.

Difference between the total mass of a nucleus's separate nucleons and the mass of the bound nucleus; multiplied by the square of the speed of light it gives the nuclear binding energy.

Time for half the nuclei in a radioactive sample to decay; it is constant for a given isotope, independent of sample size, and gives the decay constant through the natural logarithm of two.

Number of nuclear decays per unit time in a sample, measured in becquerels; it falls exponentially with time and equals the decay constant multiplied by the number of undecayed nuclei.