Quantum Physics Made Simple

Half Life The half-life of a radioactive isotope is the time it takes for half of an isotope to decay into another element. It is a measure of the stability of an isotope; the shorter the half life, the less stable the atom. Hertzsprung-Russell Diagram The H-R (Hertzsprung-Russell) diagram is a diagram used in stellar astronomy to plot the properties of stars. There are two equivalent forms. One is the observer’s form which plots the color of the star on one axis and the absolute magnitude on the other axis. Holography Holography (from the Greek, holos whole + graphe writing) …

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Galvanometer An instrument for measuring small currents. When a current is passed through a coil in a magnetic field, the coil experiences a turning force proportional to the current. Gamma Rays Are an energetic form of electromagnetic radiation produced by radioactivity or other nuclear or subatomic processes such as electron-position annihilation. Gamma rays are more penetrating than either alpha or beta radiation, but less ionizing. They are a form of electromagnetic radiation. Gamma rays are distinguished from X rays by their origin. Gamma rays are produced by nuclear transitions while X-rays are produced by energy transitions due to accelerating electrons. …

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Field Effect Transistor (FET) A type of transistor commonly used for amplifying weak-signal. The current flows down the channel between the source (source of electrons) and the drain. The amount of current that flows is regulated by the “Gate”, a small change in the voltage at the gate can increase the current flow in the channel dramatically. Fissile Material Isotopes which can undergo nuclear fission. Example of fissile materials are Uranium-233, uranium-235, plutonium-239, plutonium-241. Fission Is a nuclear process in which a heavier unstable nucleus divides or splits into two or more lighter nuclei, with the release of substantial amounts …

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East-West Effect The amount of cosmic rays coming from the west is greater than the amount coming from the east. This is due to the fact that the cosmic rays are mainly positive therefore, the positive rays are deflected by the Earth’s magnetic field. Discovered by Luis Walter Alvarez. Eclipse Is when an object moves into the shadow of another.  Lunar Eclipse Where the shadow of the Earth falls on the moon. Solar Eclipse Happens when the shadow of the moon falls on the Earth. Elastic Limit Maximum stress that a material can withstand before it is permanently deformed – once …

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Decibel (dB) A bel is a unit for comparing the levels of sounds and a decibel is a tenth of a bel. If P1 and P2 are two power levels then 1dB = 10 log (P2/P1) dB. Density Mass per unit of volume and is measured in Kg/m Dewar Flask A double-walled vessel with a vacuum between the walls to reduce the transfer of heat. The inner vessel is usually made of glass as it is a poor conductor of heat and has a reflective costing that prevents radiation. The dewar flask is now traded as the Thermos flask. It was invented …

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Barometer A device to measure atmospheric pressure. Balmer Series A series of sharp spectral lines in the hydrogen spectrum. Named after J.J. Balmer. Bar A unit of pressure nearly identical to the atmosphere unit. One bar = 750.062 torr = 0.9869 atm = 100,000 Pa. Becquerel (Bq) Is a derived SI unity of radioactivity. 1 Bq one atom per second will decay. Named after Antoine Henri Becquerel. Beta Decay A radioactive process in which a neutron changes into a proton and emits an electron and an anti-neutrino. Bimetallic Strip A strip of two metals joined together and as different metals …

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Absolute Temperature The lowest possible temperature possible – at this temperature there is no movement or vibration in the atoms. The temperature is 0 K or -273 C Acceleration The rate of change of velocity measured in m/s/s. Aberration, Astronomical Is a difference in the position of a star due to the motion of the earth. Aberration, Chromatic Is caused by the dispersion of the lens material, the variation of its refractive index n with the wavelength of light. Since the focal length f of a lens is dependent on n, if follows that different wavelengths of light will be …

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