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Capacitors isolate the stages with regard to DC, but allow them to operate at the same AC potential.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 101
capacitive feedback (electronic circuit). A process in which part of the energy in the output of an
electronic circuit is fed back to the input through a capacitor.
capacitive load (electrical circuit). An electrical load that produces more capacitive reactance than
inductive reactance in the circuit. Current leads the voltage in a capacitive load.
capacitive reactance. Opposition to the flow of alternating current caused by capacitance in the circuit.
Capacitive reactance, whose symbol is XC, is measured in ohms and is determined by the
capacitance in the circuit and the frequency of the AC.
The formula for capacitive reactance is:
XC = 1 / (2π f C)
XC = Capacitive reactance in ohms
2π = A constant, 6.28
f = Frequency of the AC in hertz
C = Capacitance in farads
capacitive time constant. The amount of time, measured in seconds, needed for the voltage across a
capacitor to rise to 63.2% of the source voltage. The time constant is determined by the resistance and the
capacitance of the circuit.
The formula for capacitive time constant is:
TC = R C
TC = Time constant in seconds
R = Resistance in ohms
C = Capacitance in farads
capacitor. An electrical component made of two conductors separated by an insulator, or dielectric. A
capacitor can store an electrical charge in an electrostatic field. The capacitance of a capacitor is measured
in farads, microfarads (10-6 farad), or picofarads (10-12 farad).
The capacitance of a capacitor is determined by three things: the area of the plates, the amount of
separation between the plates, and the kind of insulating material, or dielectric, between the plates.
Capacitors were at one time called condensers.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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capacitor-discharge ignition system (gas turbine engine ignition system). A type of high-energy
ignition system that produces a hot spark for starting a gas turbine engine.
In a capacitor-discharge ignition system, electrons are stored under high voltage in capacitors.
When these electrons are released, they cause a high-intensity spark to jump across the gap in the igniters.
capacitor-input filter (electronic filter). A type of electrical filter used to smooth the pulsations in the
output of an electronic power supply. A capacitor is installed in parallel with the rectifier output, and an
inductor is in series.
capacitor-start induction motor. An AC motor whose rotor is excited by voltage induced into it from the
stator windings. A capacitor-start motor has two stator windings: a start winding and a run winding. The
start winding is in series with a capacitor that shifts the phase of the current flowing through it, so it is out
of phase with the current flowing through the run winding.
The magnetic field produced by the start winding and the field produced by the run winding work
together to produce a magnetic field that rotates within the motor housing. The rotor follows this rotating
field. When the rotor has accelerated to a specified speed, a centrifugal switch opens the start winding
circuit, and the motor continues to operate on the run winding alone. Capacitor-start motors have a good
starting torque.
capacity (battery specification). The total amount of current available in a battery or electrical cell.
Capacity is normally measured in ampere-hours.
cap cloud (meteorology). A standing, or stationary, cap-like cloud crowning a mountain summit.
cape chisel. A narrow-blade cold chisel with either a single or double bevel. Cape chisels are used to knock
the head off a rivet after it has been drilled through, and to cut narrow grooves and keyways in metal
components.
capillary action. The action that causes a liquid to climb the walls of a container or to be drawn up into
extremely tiny tubes or between close-fitting parts.
The force of adhesion between the liquid and the solid wall of the container is greater than the
force of cohesion between the molecules of the liquid. The stronger force of adhesion causes the liquid to
try to spread out and wet the walls.
Capillary action causes a piece of blotting paper to pick up a liquid, and the lack of capillary
action causes a drop of water to form into a ball on a waxed surface.
capillary tube. A metal or glass tube with such a small inside diameter that capillary action causes liquid to
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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move in the tube.
A soft copper capillary tube is used with a vapor-pressure thermometer connecting the
　
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