Geomagnetic Storms - Intense world-wide variations in the Earth's magnetic fields. They are associated with the occurrence of sunspots and solar flares.
Galactic Poles - The poles defined on the celestial sphere by the intersection with the sphere of a line through its centre drawn normal to the plane of circular symmetry of the Galaxy:
Gamma-Rays, Delayed - Gamma-rays emitted in the decay of fission products. They represent about 3% of all γ-rays emitted as a result of fission.
Gamma-Ray Spectrometer - An instrument designed for measuring the distribution of energy and intensity in γ-ray spectra. Such an instrument usually involves the use of scintillation techniques, proportional counters, or spectroscopy by crystal diffraction.
Gamma-Ray Spectrum - The emission spectrum of sharp lines, corresponding to well-defined quantum energies, resulting from unclear transitions between two or more energy states.
Gamma-Rays, Prompt - Gamma-rays accompanying fission without measurable delay.
Gas. A state of matter in which the mol cules move freely, so that a gas will completely fill the region in which it is contained. A substance which is in the gaseous state but below the critical temperatute is generally described as a vapour.
Gas Amplification: Gas Multiplication - (I) The process whereby, in a sufficiently strong electric field, the ions produced in a gas by ionizing radiation produce additional ions. (2) The factor by which the initial ionization in (1) is multiplied.
Gas Constant: Molar Gas Constant - The constant of proportionality R in the equation of state for a perfect gas, pv = RT, referred to one mole of gas. In this equation p is the pressure, v the volume, and T the absolute temperature. R is equal to 8.314 JlK, or 1.985 cal/K. It may be interpreted as being two-thirds the total kinetic energy due to transitional motion of the molecules of an ideal gas at 1. K.
Gas Dynamics - The study of the dynamics and thermodynamics of flowing gases and vapours.
Gas, Perfect: Gas, Ideal - A gas which behaves as an assembly of perfectly elastic spherical "point" masses in random motion which exert no forces on each other except during collisions. The behaviour of such a gas is described by seven well-recognized "law's", the perfect-gas laws.
Gas Scrubbing - The treatment of a gas with a liquid, usually water, to remove particulate or gaseous components.
Gas turbine - An internal combustion engine in which mechanical energy. is obtained from the expansion of a high-temperature, high-pressure gas stream provided by the combustion of a suitable fuel with compressed air. ,The expanded gas drives the compressor via a turbine, and may either drive a second turbine to provide shaft power, or may be expanded to atmospheric pressure in the exhaust system to provide a jet of high-velocity gas for propulsion. In the turbo-jet both methods are used, with the emphasis on the first. Gas turbines are used for aircraft propulsion; marine, locomotive, and automobile propulsion; stationary power plants; and as ancillaries in industrial plant.
Gauge - (1) An instrument or device for measuring dimension, pressure, or other physical property. (2) The condition imposed upon the vector and scalar potentials of an electromagnetic field to achieve symmetry (gauge invariance).
Gauss - The CGS unit of magnetic induction or flux density. It is equal to 1 line (or Maxwel1) per cm2 and to 10-4 tesla.
Gauss theorem - States in general that the total flux of a vector field through a closed surface is equal to the volume integral of the divergence of the vector taken over the enclosed volume. It may be applied to surfaces drawn in electric and magnetic fields, and to gravitational magnetostatic, and fluid-velocity fields. Thus, for example, the electric flux trom an enclosed electric charge q is and the magnetic induction is zero.
Gay-Lussac Law - For a perfect gas: states that the volumes in which gases combine chemically bear a simple whole-number relation to each other and to that of the resulting product if that is also gaseous, and if measured at the same temperature and pressure.
Geiger Law - A relationship between the initial velocity of a-particles and their range, applicable to range, applicable to ranges from 3. to 7 cm. It states that V3 = Ar, where v is the initial velocity, r the range, and A a constant.
Geiger-Nuttall Rule - A rule originally relating the lifetime of an α-emitter to the range of the particles but now usually expressed in terms of the decay energy as follows: logλ. = a + b log E, where n is the decay constant, E the kinetic energy of the emitted (α-particle, and a and b are constants appropriate to each of the three naturally occurring radioactive familes.
Geiger Regio - In a Geiger-Muller counter: that range of operating voltage over which the output charge is independent of the number of primary ions produced by the initial ionzing event.
Galaxy - A flattened system of stars, dust, and gas, which includes the Sun and at. least all stars that are visible to the naked eye. It has a diameter of about 25 kiloparsecs (kpc) and central thickness of about 5 kpc, with a mass about 1.6 ×10ll times that of the Sun. The Galaxy is popularly known as the Milky Way. By extension. any similar system of stars etc, is known as a galaxy. (Note: I parsec ≈ 3.0857× 1016 metres).
Galaxy Machine - An acronym for General Automatic Luminosity and XY, referring to a machine which can extract the vast amount of stellar information recorded on photographic plates at a rate comparable with the rate at which the information is produced. The machine finds the stellar images and measure their positions, sizes, and densities, all automatically, at a rate of 1000 images an hour, the size and density being a measure of the strength of such an image.
Gallon - (1) The fundamental unit of volume in the Imperial system of measurement. By definition, it is the volume of 10 Imperial pounds of distilled water at 62°F at a barometric pressure of 30 in: (2) The United States unit of volume, defined as the volume of 231 in3. One Imperial gallon is 1.20094 US gallons, and one US gallon is 0.83267 Imperial gallons. (Note: 1 Imperial gallon = 4,,5461 dm3.)
Galvanomagnetic Effects - Phenomena in which a potential difference is developed as a result of the presence of a magnetic field, as in the Hall effect, which is defined separately.
Galvanometer - An instrument for measuring electric current by its magnetic effect, in which observations are made of the deflection produced by the torque exerted between an electric circuit in a coil and a magnet. In an astatic galvanometer the coil is stationary and the magnet turns. In a moving-coil galvanometer the reverse is the case.
Galvanometer, Ballistic - A galvanometer designed to measure the total quantity of electricity in a transient current. The period of swing of its moving element is long compared with the time of discharge so that the amplitude of the first oscillation of the galvanometer is proportional to the quantity of electricity to be measured.
Galvanometer, D'arsonval - The best-known form of moving-coil galvanometer. It is practically undamped and if fitted with a heavy coil can also be used as a ballistic galvanometer. It is, however. normally fitted with a light coil. The current to be measured passes through the coil via the suspension.
Galvanometer, Tangent - A galvanometer in which a small magnetic needle is mounted at the centre of a circular coil, the current being proportional to the tangent of the angle of deflection.
Geomagnetism - The study of the Earth's magnetic field and its secular and transient variations.
Geometrical Optics - The treatment of light paths as a series of rays. Diffraction, interference, and polarization effects are ignored and there is straight-line propagation in a homogeneous medium.
Geophysics - That branch of physics which correlates and explains certain natural phenomena occurring in the Earth and its environs. The term is also used in a restricted sense to mean the physics of the solid Earth.
GeopotentiaI - At a given point in the atmosphere: the gravitational
potential energy of unit mass located at that point.
Geothermal gradient - The rise in temperature of the Earth's crust with increasing depth.
Getter - A material introduced into a vacuum enclosure to establish and maintain a very low pressure (10-8 mm of mercury or less) of residual gas. Materials commonly used are phosphorus, zirconium, titanium, and charcoal.
Ghosts. (1) Spectral ghosts. (2) Spurious images seen on a televIsion screen and arising from echoes.
|
