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Define the terms "capacitor" and "capacitance."
- A capacitor is a device that stores electrical energy in an electrostatic field.
- Capacitance is the property of a circuit which opposes changes in voltage.
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State four characteristics of electrostatic lines of force.
- They are polarized from positive to negative.
- They radiate from a charged particle in straight lines and do not form closed loops.
- They have the ability to pass through any known material.
- They have the ability to distort the orbits of electrons circling the nucleus.
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An electron moves into the electrostatic field between a positive charge and a negative charge. Toward which charge will the electron move?
Toward the positive charge.
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What are the basic parts of a capacitor?
Two pieces of conducting material separated by an insulator.
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Define the term "farad."
A farad is the unit of capacitance. A capacitor has a capacitance of 1 farad when a difference of 1 volt will charge it with 1 coulomb of electrons.
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What is the mathematical relationship between a farad, a microfarad, and a picofarad.
- One microfarad equals 10^-6 farad. (.000001)
- One picofarad equals 10^-12 farad. (.000000000001)
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State three factors that affect the capacitance of a capacitor.
- The area of the plates.
- The distance between the plates.
- The dielectric constant of the material between the plates.
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Name two types of power losses associated with a capacitor.
- Hysteresis
- Dielectric leakage
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Define the term "working voltage" of a capacitor. What should be the working voltage of a capacitor in a circuit that is operating at 600 volts?
- It is the maximum voltage the capacitor can work without risk of damage.
- 900 volts.
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State what happens to the electrons in a capacitor circuit when (a) the capacitor is charging and (b) the capacitor is discharging.
- (a.) When the capacitor is charging, electrons accumulate on the negative plate and leave the positive plate until the charge on the capacitor is equal to the battery voltage.
- (b.) When the capacitor is discharging, electrons flow from the negatively charged plate to the positively charged plate until the charge on each plate is neutral.
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At what instant does the greatest voltage appear across the resistor in a series RC circuit when the capacitor is charging?
At the instant of the initiation of the action.
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What is the voltage drop across the resistor in an RC charging circuit when the charge on the capacitor is equal to the battery voltage?
Zero.
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What is the RC time constant of a series RC circuit that contains a 12-megohm resistor and a 12-microfarad capacitor?
- 144 seconds (t = R x C)
- (144 seconds= 12,000,000 x .000012)
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What is the total capacitance of a circuit that contains two capacitors (10 �F and 0.1 �F) wired together in series?
- Ct = 1�F or .099 �F
- (Ct= C1 x C2 / C1 + C2)
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What is the total capacitance of a circuit in which four capacitors (10 �F, 21 �F, 0.1 �F and 2 �F) are connected in parallel?
- Ct = 33.1 �F
- (Ct = C1 + C2 + C3 + C4)
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An oxide-film dielectric is used in what type of capacitor?
Electrolytic capacitor
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A screw adjustment is used to vary the distance between the plates of what type of capacitor?
Trimmer capacitor
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