Basic Electrical Theory. (Unit 17) Capacitance.
Three capacitors, a 12 μF, a 20 μF, and a 30 μF, are connected in parallel to a 400 Hz source. What is the total XC?
6.42 Ω.
Factors that determine the capacitance of a capacitor are the _____ the plates.
surface area. distance between. dielectric between.
Two capacitors, a 20 μF and a 30 μF, are connected in series. What is the total capacitance?
12 μF.
Two capacitors, a 20 μF and a 30 μF, are connected in series to a 400 Hz source. What is the total capacitive reactance?
33.16 Ω.
Two capacitors, a 20 μF and a 30 μF, are connected in parallel. What is the total capacitance?
50 μF.
Three capacitors, a 12 μF, a 20 μF and a 30 μF, are connected in series. What is the total capacitance?
6 μF.
Two capacitors, a 20 μF and a 30 μF, are connected in parallel to a 400 Hz source. What is the total capacitive reactance?
7.96 Ω.
If a capacitor becomes overcharged, the electrons from the negative metal plate can be pulled through the insulation (dielectric) to the positive metal plate by an excessive electric field.
True.
When alternating current is applied to a capacitor, the current continuously moves back and forth charging and discharging the capacitor.
True.
The opposition offered to the flow of alternating current by a capacitor is called "capacitive reactance," is expressed in ohms, and abbreviated _____.
XC.
Capacitance is measured in units of _____.
farads.
What is the reactance of a 25 μF capacitor when the applied frequency is 400 Hz?
15.92 Ω
A 1 μF capacitor has 2,652 Ω of reactance at 60 Hz. What is the reactance value at 400 Hz?
397.88 Ω.
Three capacitors, a 12 μF, a 20 μF and a 30 μF, are connected in parallel. What is the total capacitance?
62 μF.
A half-wave rectifier can be used to convert ac voltage into dc voltage to continuously charge a capacitor.
False.
Capacitors are used to start single-phase ac motors and to prevent arcing across the contacts of electric switches.
True.
Even when power is removed from the circuit, capacitors can store large amounts of energy for a long period of time, and can discharge and arc if inadvertently shorted or grounded out.
True.
Frequency is expressed as "cycles per second," or "Hertz" (Hz).
True.
When a capacitor has a potential difference between the plates, it is said to be _____. One plate has an excess of free electrons, and the other plate has a lack of them.
charged.
To discharge a capacitor, all that is required is a(n) _____ path between the terminals of the capacitor. The free electrons on the negative plate then flow through the external circuit to the positive plate.
conductive.
If a capacitor is overcharged, the electrons from the negative plate can be pulled through the insulation to the positive plate. The capacitor is said to have _____.
shorted.
A capacitor can be thought of as a device that resists changes in current. Because a capacitor introduces reactance to the circuit, it shifts the current waveform to _____.
lead the applied voltage by 90°.
