# AC theory Part 2

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 Author: johnbowens ID: 124557 Filename: AC theory Part 2 Updated: 2012-01-14 23:46:32 Tags: Ac theory JATC IBEW NJATC capacitance Folders: Description: Ac theory in partnership with the NJATC 2009 copyright Show Answers:

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1. Capacitance is measured in what? AC Theory, NJATC 2009 PP 91
2. Capacitors have the characteristic to oppose what? AC Theory, NJATC 2009 PP 91
To oppose a change in voltage.
3. Capacitors are used to block and pass what? AC Theory, NJATC 2009 PP 91

Regarding the above statement, do the electrons pass through the insulating dielectric and/ or exert electrical pressure? AC Theory, NJATC 2009 PP 91
Block DC and pass AC

The electrons do not pass through the dielectric plate but do exert electric pressure.
4. Using scientific notation, what is Micro, Nano, and Pico? AC Theory, NJATC 2009 PP 91
• Micro 10>6
• Nano 10>9
• Pico 10>12
5. The symbol for a fixed and variable capacitor is what? AC Theory, NJATC 2009 PP 91
6. The general formula for capacitance is what? AC Theory, NJATC 2009 PP 92

This formula is used to do what? AC Theory, NJATC 2009 PP 92
• C = Q/V
• where:
• C= capacitor value in farads
• Q= charge in coulombs
• V= voltage applied

This formula is used to compare the charge a capacitor can hold per volt that is applied to the capacitor. The larger the plates the more the voltage.
7. Capacitors ________ to oppose a change in ______. AC Theory, NJATC 2009 PP 93
• appear
• voltage
8. The formula for calculating the capacitance of a capacitor measured in farads is? AC Theory, NJATC 2009 PP 92
• C = .225AK/10^6D
• where:
• C = capacitance in microfarads
• A = cross-sectional area of one plate in square inches
• K = dielectric constant of the material between the plates (for air K is 1)
• d = the thickness of the dielectric (or the distance between the plates) measured in inches
9. What is the relationship between the current and voltage in a capacitor? AC Theory, NJATC 2009 PP 97
The current in the capacitor circuit leads the voltage across the capacitor by 90 electrical degrees.
10. Capacitors designed for use in AC circuits are considered what? AC Theory, NJATC 2009 PP 98
Non-polarized, meaning no specific voltage polarity.
11. What abbreviation means that a capacitor is rated for a maximum voltage in DC terms? AC Theory, NJATC 2009 PP 99
WVDC: working volts DC
12. Polarized capacitors are indicated how and used in what type of voltage? AC Theory, NJATC 2009 PP 99
By a positive or negative marked leads and used only in DC voltage.
13. The plate with a lack of electrons in a capacitor has a ______charge, where the plate with an excess of electrons has a ______ charge. AC Theory, NJATC 2009 PP 100
• positive
• negative
14. What is the relationship between the voltage rating and the thickness of the dielectric in a capacitor? AC Theory, NJATC 2009 PP 104
The voltage rating is decreased proportionally to the thickness of the dielectric.
15. How do you test a capacitor? AC Theory, NJATC 2009 PP 105

What are the symptoms of a leaky / shorted capacitor?
By using an ohm-meter and watching for an ohmic spike as he capacitor charges and current flow decreases, and then as current ceases an infinite ohmic value is given.

• Leaky: current flows = never reaches infinite ohms
• Shorted: current flows = really low ohmic value
16. Capacitors charge and discharge at an exponential rate when connected with what? AC Theory, NJATC 2009 PP 106

Proven by the Time Constant formula for capacitors which is what?
When connected with resistors or in series with resistors

T=RxC
17. Is there Capacitive reactance in a D.C. circuit and what does it oppose? AC Theory, NJATC 2009 PP 110

What is the formula for capacitive reactance?

What does this formula show?
NO, capacitive reactance only exists in an AC circuit and it opposes current.

XC= 1/ (2pieFC)

That as the frequency increases XC decreases, or that they are inversely proportional to each other.
18. What is the formula for Capacitance? AC Theory, NJATC 2009 PP 113
C=1/(2pieFXc)
19. Inductors store energy in a _________, and capacitors store energy in a__________. AC Theory, NJATC 2009 PP 91
• magnetic field
• electrostatic field
20. It has two leads, the anode and the cathode, which is where it gets its name from. http://www.funtrivia.com
Diode
21. ______ were used for logic circuits in some of the earliest computers. They were later replaced by modern semiconductors and are used to switch high voltage circuits. http://www.funtrivia.com
Relays
22. This is a type of semiconductor in which the flow of current can be controlled though a base or gate terminal it is usually used for electronic switching or amplifiers. http://www.funtrivia.com
Transistor
23. This consists of usually two coil windings which usually share a magnetic core. It is used to convert an ac source or signal into another ac source or signal with same power (ideally) but different voltage and current. http://www.funtrivia.com
transformers
24. This is a special type of diode that breaks down when a critical reverse voltage is applied. it is most commonly used to regulate voltage. http://www.funtrivia.com
Zener diode
25. This is a special type of diode that lights up when a small voltage is applied. They are usually used as indicators or in numerical or alphanumerical displays. http://www.funtrivia.com
LED. LED's use mili-amps and therefore large amounts of power is displays and therefore LCD's using milliamps are preferred.
26. A multi-segment rotating connection that is connected to the armature windings defines what term? AC Theory NJATC 2nd Ed. 2009, PP 341
A Commutator is connected to this.

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