F

f number - ratio of the focal length of a lens to its diameter e.g f/4
Fahrenheit scale - temperature scale where the melting ice is 32 ^oF and boiling water 212 ^oF
farad - unit of capacitance (symbol F)
fast breeder reactor - a nuclear fission reactor that produces more fuel than it uses
fast neutrons - energetic, high speed neutrons produced during nuclear fission
feedback - returning a fraction of the output to the input of a device such as an amplifier
femto - one thousand million millionth (10^-15) as in femto metre
fermi - one thousand million millionth (10^-15) of a metre
ferrite - a material made of a metallic oxide and a low density ceramic oxide of iron
ferromagnetic - material with magnetic domains, e.g. iron and steel
fibre optics - method of transmitting light (usually laser light) down a thin glass fibre
field - region around an energy source affected by that source, as in magnetic, electric
field of view - angular diameter of the region visible through a telescope
field effect transistor - transistor where the current depends on the motion of majority carriers alone
filament - fine wire in a light bulb that glows when a current is passed through it
finder - a small telescope with a wide field of view fixed to the top of a larger telescope
first harmonic - in music the fundamental frequency of vibration
fish-eye lens - lens giving a wide angle but distorted field of view
fissile - material that can undergo (nuclear) fission
fission - splitting apart, as with neutrons and uranium in nuclear fission.
floating - this happens when the density of the object is less than the density of the liquid
fluid - a material that takes the shape of its container – e.g. liquid or a gas
fluorescence - the emission of light from an object immediately following absorption of radiation
flux - flow of energy in a field, as in magnetic flux
flux density - the concentration of flux in a field
FM - frequency modulated
focal length - distance from lens or mirror to the principal focal point
focal plane - flat surface on which a lens or mirror forms an image, as in 'focal plane shutter'
force - a push or pull on an object
forced vibrations - motion of a vibrating system that is acted on by an external force
fragment - piece
frame of reference - 'background' (coordinate system) relative to which we take measurements
Fraunhofer lines - dark absorption lines in the spectrum of the Sun
free electrons - electrons in a metal not bound to any particular atom
free fall - object falling freely in a gravity field, no resistance
freezing point - temperature at which a liquid changes to a solid
freezing mixture - mixture of ice and salt (e.g.) to give low temperatures (down to –15^oC or so)
frequency - number of vibrations of an object or wave every second
frequency modulation - modulation where the frequency of the carrier wave is changed
fresnel biprism - apparatus for demonstrating interference and measuring the wavelength of light
friction - a resisting force when one object moves over (or though) another
fringes - areas of destructive and constructive interference
fuel cell - apparatus for making electrical energy directly from an oxidation/reduction process
fulcrum - pivot point
fundamental - basic, as in fundamental frequency
fundamental particles - ones that cannot be spilt into smaller ones, e.g. quarks and leptons
fuse - device (often a wire) that breaks when the current through it is too large
fusion - joining together as in nuclear fusion. Two deuterium atoms make one helium