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.
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.
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.
What are the basic parts of a capacitor?
Two pieces of conducting material separated by an insulator.
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.
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)
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.
Name two types of power losses associated with a capacitor.
- Dielectric leakage
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.
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.
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.
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?
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)
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)
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)
An oxide-film dielectric is used in what type of capacitor?
A screw adjustment is used to vary the distance between the plates of what type of capacitor?