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F 1. Symbol for FORCE. 2. Symbol for FLUORINE.
3. Abbreviation of FAHRENHEIT. 4. Abbreviation
of FARAD. 5. Abbreviation of FERMI. 6. Symbol
for FOCAL LENGTH. 7. Symbol for FUSE.
8. Symbol for FARADAY CONSTANT.
f 1. Abbreviation of FEMTO. 2. Symbol for FRE-
QUENCY. 3. Symbol for FUNCTION.
F 0 Symbol for DAMPING FACTOR.
F1 layer The lower part of the ionosphere’s F RE-
GION. Also called F1 region.
F2 layer The upper part of the ionosphere’s F RE-
GION. Also called F2 region.
fA Abbreviation of FEMTOAMPERE.
fabrication tolerance The amount of variation
that can be tolerated in the manufacture of components.
Fabry-Perot interferometer A resonant cavity, often
used with lasers, that has mirrors at each
end; the interferometer produces the optical
equivalent of standing waves.
face 1. A flat crystal surface whose orientation can
be expressed as its position relative to other
faces. 2. The viewer’s side of a screen. 3. The
scale part of a meter.
face material In a tape recorder, the plastic used
to coat the face of a head.
face-parallel cut See Y-CUT CRYSTAL.
face-perpendicular cut See X-CUT CRYSTAL.
face side The side of pressure-sensitive insulating
tape that is coated with adhesive.
facom A radionavigation system that operates by
means of phase comparison at low frequencies.
Effective over long distances and under poor conditions.
facsimile Also called fax. The transmission and reception,
through the medium of radio or by wire,
of permanent pictures, writing, and other graphic
material.
facsimile receiver The complete device or system
that selects, amplifies, and demodulates a picture
signal received up from the air, wires, or cable,
and uses the elements of this signal to reproduce
the picture. Also see FACSIMILE.
facsimile recorder The machine that puts a transmitted
facsimile image on paper.
facsimile transmitter The complete device or system
that generates signals depicting graphic material
(pictures, writing, printing, etc.) and sends
them to a distant point via cable, wire lines, or radio
for subsequent reproduction. Also see FAC-
SIMILE.
factor
1. A data element that is an operand in an
arithmetic operation. 2. To find the two or more
numbers whose product is the number being factored.
3. One of two or more numbers whose
product is the number being factored.
factorial
Symbol, !. For an integer n, the product of
all positive integers up to and including n. Thus,
5! = 1 × 2 × 3 × 4 × 5 = 120. The term n! is read “n
factorial.”
factor of merit See FIGURE OF MERIT.
factor of safety See SAFETY FACTOR.
fade in To gradually increase an audio or video signal—especially
for recording.
fade out 1. To gradually decrease an audio or video
signal—especially for recording. 2. The complete
disappearance of a radio communications signal.
See FADING.
fader
1. In sound amplification systems, an attenuator
circuit that enables the operator to fade out
one signal and fade in another. Ordinarily, a
fader does not provide mixing action. 2. In an au-
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