Page 72 - The Illustrated Dictionary of Electronics

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backbone • back resistance 57

backbone A form of transmission line with capaci- cone feeds sound into the same area through a
tive connections between the generator and the folded horn.
load. backloading In a cascaded series of amplifiers, the
back conduction Conduction of current in the re- tendency of loading effects to be passed to earlier
verse direction, as across a semiconductor junc- stages. A change in the output impedance of a fi-
tion that is reverse-biased. nal amplifier circuit, for example, could also re-
back contact A contact that closes a circuit when a sult in a change in the output impedance of the
relay, switch, or jack is in its normal rest position. driver circuit, and perhaps even in a change in
back current Symbol, I b . The normally small cur- the output impedance of the predriver.
rent flowing through a reverse-biased pn semicon- back lobe In the pattern of a directional antenna,
ductor junction. Also called reverse current and the lobe directly opposite the major lobe, repre-
inverse current. Compare FORWARD CURRENT. senting the radiation or response in or from a di-
back diode A semiconductor diode that is normally rection 180 degrees from that in which the gain is
back-biased (reverse-biased). greatest.
back echo An echo resulting from the rear lobe of
an antenna radiation pattern.
back emf See BACK VOLTAGE.
Back-Goudsmit effect See ZEEMAN EFFECT.
background 1. The context or supporting area of a
picture (e.g., the background of a television pic-
ture). 2. Background noise.
background control In a color television receiver,
a potentiometer used to set the dc level of the
color signal at one input of the three-gun picture
tube.
background count Residual response of a ra-
dioactivity counter in an environment as free as
practicable of radioactivity. This background is
caused largely by cosmic rays and inherent ra-
dioactivity of surrounding buildings and other
bodies.
background job A low-priority, relatively long-
running computer program that can be inter-
rupted so that a higher-priority program can be
run.
background noise Electrical noise inherent to a
particular circuit, system, or device that remains
when no other signal is present. backplate A flat electrode in a television (TV) cam-
background processing In a computer, the run- era tube that receives the stored-charge image via
ning of programs having low priority. capacitive coupling.
background radiation Nuclear radiation from ma- back porch In a television (TV) horizontal sync
terials in the environment. Also see BACK- pulse, the time interval between the end of the
GROUND COUNT. rise of the blanking pedestal and the beginning of
background response The response of a radiation the rise of the sync pulse. That portion of the flat
detector to background radiation. top of the blanking pedestal behind the sync
backing store In a computer, a device that stores pulse. Compare FRONT PORCH.
large amounts of information. In most small com- back-porch effect In transistor operation, the con-
puters, this is done via MAGNETIC DISK and/or tinuation of collector-current flow for a short time
MAGNETIC TAPE. A backing store can also be an after the input signal has fallen to zero.
optical storage medium, such as CD-ROM (com- back-porch tilt The departure of the top edge of a
pact disk, read-only memory). back porch from true horizontal.
backlash 1. Slack or lag in action of moving parts. back pressure sensor A device that detects and
Example: delay between initial application of a measures the torque that a motor is applying,
force (such as that required to turn a knob) and and produces a signal whose amplitude is pro-
movement of a part or device (e.g., a potentiome- portional to the torque. This signal can be used
ter or variable capacitor). 2. On a mechanical for various purposes. In a robotic device, for ex-
analog tuning dial, an arc within which slack or ample, the sensor output can be fed back to the
lag is discernible. motor control to limit the applied force.
backloaded horn A loudspeaker enclosure in back resistance Symbol, R b . The resistance of a re-
which the front of the speaker cone feeds sound verse-biased pn semiconductor junction. Also
directly into the listening area, and the rear of the called REVERSE RESISTANCE.