Unit 20: Capacitors
The three factors that determine the capacitance of a capacitor are
1. The surface area of the plates 2. The distance between the plates. 3. The type of dielectric used.
A capacitor has a capacitance if ____ farad when a charge of ____ volt across its plates results in a movement of 1 _____
1/1/Coulomb
Capacitors connected in parallel
C1+C2+C3=CT
Capacitors connected in series
CT= 1/(1/C1)+(1/C2)+(1/C3)
Variable capacitors
Contain a set of movable plates and stationary plates
The rating of the dielectric material is called _________
Dielectric constant
The capacitors energy is stored in the __________
Dielectric material
Attraction causes electron orbit to stretch. Stretching of atoms of the dielectric is called _________
Dielectric stress
If a ______ capacitor connection become reversed it will not reform and be destroyed
Dry-type electrolytic
Polarized capacitors are
Electrolytic capacitors / sensitive to polarity connection (DC Capacitors)
A capacitor stores energy in an ________
Electrostatic field
Capacitors charge and discharge at an __________rate
Exponential
The basic unit of capacitance is the _________ and symbolized by the letter ___
Farad/F
The curve is divided into ____________. Each one changes by____
Five time constants/63.2%
A dry- type electrolytic capacitors has a advantage of being
Leak proof
Current flow through the dielectric is called ___________
Leakage current
Capacitors are generally rated at _______
Microfarads, nanofarads, or picofarads
Nonpolarized capacitors are
Not sensitive to polarity connection (AC capacitor)
Large AC oil filled caps can be tested for shorts with a ______ and capacitance. The dielectric strength can be tested with a ______
Ohmmeter / HIPOT
Capacitors are used for __________
Power factor correction, control frequency
Leakage current in ___________ to the ___________ of the dielectric and charge across the plate.
Proportional/resistance
When a capacitor is connected in a circuit with a resistor, the amount of time needed to charge the capacitor is _________
RC time constant (T=RxC)
Small capacitors are tested for _______ with a _____. To test for leakage apply ______ and connect to _____ and expect_____
Shorts / ohmmeter. DC / micrometer / zero current flow
A capacitor is constructed by
Sperating two metal plates by insulating material called dielectric
The greater the _______________ of the plates, the more capacitance a capacitor will have
Surface area
__________ indicates the amount of capacitance change with temp.
Temperature coefficients
Current can only flow when
The capacitor is charging or discharging
Capacitors are devices that oppose a change in
Voltage
If polarity of a ______ capacitor becomes reversed, the capacitor becomes shorted but if corrected can be resotred
Wet-type capacitor
Capacitors have the ability to supply almost ____ amount of current. capacitors have enough energy to cause _____
infinite, a persons heart to fibrillate
The greater the ______ the more capacitance a capacitor will have
surface area of the plates
