AC Theory Lvl. 1 L1-5

The following is missing from this review

4Q25 b/ it's easy enough to ignore. =P

How many time constants does it take for current to reach its maximum value in an inductive circuit?

5 1Q15

How many time constants are required to charge a capacitor to a level where it is considered to be fully charged?

5 4Q21

How many time constants for a capacitor to fully discharge?

5 4Q21

When a graph is used to represent the rate-of-charge of a capacitor, it is broken down into ? time constants.

5 5Q14

What is the formula for inductance?

L = ( 0.4 * pi * N^2 *A* µ)/(l) Wherein: A = Cross sectional area of the core l = Length of core used N = Number of turns µ = Permeability of the type of core material used 1Q20

At what percentage is the current after two time constants?

86.4%

At what percentage is the current after three time constants?

94.9%

? charge is the term used to describe the stationary charge stored in a capacitor.

Electrostatic 5Q8

? Law states that an induced voltage or current opposes the motion that causes the induced voltage or current.

Lenz's 1Q8

Inductance is measured in ?.

Henries 3Q3

Capacitors ? at an exponential rate. I. charge II. discharge

I & II 5Q13

Current can flow only during the period of time that a capacitor is ? . I. charged II. charging III. discharged IV. discharging

II & IV 4Q11

Whenever an electric current flows through a conductor, a magnetic field is formed ? the conductor.

Around 1Q7

When a capacitor is connected in a circuit with a resistor, the amount of time needed to charge the capacitor is determined by the ? .

RC time constant 4Q22

What is the formula for determining the time constant in an inductive circuit?

T = L / R 1Q22

What is the formula to find a capacitors time constant.

T = R * C 5Q19

True or False A picofarad is also called a micromicrofarad and may be abbreviated µµF.

True 4Q6

Applying reverse polarity to polarized capacitor can cause dielectric breakdown and excessive current flow through the capacitor

True 5Q16

True of False A capacitor that has a high level of current flow through its insulating material would be considered to have a weak (or Leaky) dielectric

True 5Q6

True or False Current does not flow through a capacitor, but when connected to an alternating voltage supply, current appears to flow through the capacitor

True 5Q6

True or False When a capacitor becomes charged, a potential exhists between the plates of the capacitor.

True 5Q6

True or False An AC ammeter indicates a steady current when it is connected in series with a capacitor across an AC source.

True Note: Current cannot flow through a capacitor, but it does flow from one conductive plate to the other conductive plate each half cycle. The meter indicates a steady current while the capacitor's dielectric blocks electrons from flowing across the dielectric and actually flowing through the capacitor. 4Q17

Which items listed below are factors that work in combination to affect the inductance produced by an inductor. I. Cross sectional area of the core II. Number of turns of wire III. Permeability of the core material IV. Spacing between the turns V. All the Above

V. 1Q12

When no current flows in a conductor, free electrons move ? , and their magnetic fields cancel.

at random 1Q2

The direction of induced ? flow through a conductor is determined by the direction of the magnetic field surrounding the conductor and the direction the conductor is traveling through the magnetic field.

current 1Q1

Inductors always oppose a change of ? .

current 1Q9

When the dielectric of a capacitor is broken down, excessive ? will flow through the dielectric, shorting it.

current 5Q12

The term ? refers to the force holding an electrical charge across a capacitor's plates.

electrostatic 4Q12

The ? field is formed when electrons are removed from one plate and deposited on the other.

electrostatic 4Q13

Select factors that determine the capacitance of a capacitor. a. Area of the plates (conducting surfaces) b. Distance between the plates c. The type of dielectric used (insulating material) d. All of the above

d. 4Q9

Which job can a capacitor perform in electrical work? a. Produce large current pulses b. Timing circuits c. Power factor correction d. All of the above

d. 5Q1

Which is/are the proper safety rule(s) for working on circuits containing capacitance? Select one: a. Be sure to discharge the circuit capacitance after the circuit is turned off. b. Observe polarity marks when connecting capacitors to the circuit. c. Be sure the capacitor's voltage rating is greater than the peak voltage present in the circuit. d. All of the above.

d. 5Q23

Which physical factor determines the amount of capacitance? a. Area of the plates b. Distance between the plates c. Type of dielectric d. All of the above

d. 5Q3

If a capacitor is subjected to a voltage in excess of that for which it is designed, the electron flow may puncture the insulation, causing an arc-through, which destroys the ? and, therefore, the capacitor.

dielectric 4Q15

Air has a ? constant of 1.

dielectric 5Q11

A capacitor consists of two conductors, usually referred to as plates separated by an insulator called the ? .

dielectric 5Q2

Inductance is ? proportional to the cross sectional area of the core.

directly 1Q21

Inductance is ? proportional to the number of turns of wire.

directly 1Q21

Inductance is ? proportional to the permeability of the type of core material used.

directly 1Q21

The rate of current change in an inductive circuit can be described as a(n) ? curve.

exponential 1Q14

Electrolytic capacitors are the ? type.

polarized 5Q20

When a DC voltage source is connected to a capacitor, electrons will be moved from the plate connected to the ? and deposited on the plate connected to the ? pole. This will continue until the voltage across the capacitor equals the voltage source.

positive / negative 4Q10

Whenever a conductor cuts through magnetic lines of flux, a ? is induced into the conductor.

voltage 1Q1

A capacitor has the capacitance of one ? when a change of one volt across its plates results in the movement of one coulomb of electrons.

farad 5Q5

The unit of capacitance is the ? and is symbolized by the letter ? .

farad / F 5Q4

Capacitors often have their ? value and ? rating printed on them.

farad / voltage 5Q22

The length of one time constant is dependent on the ? of the capacitor and the resistance in series with the capacitor.

farad rating 5Q17

The important factors needed for generation of an induced voltage are a conductor, a magnetic field, and ? .

relative motion 1Q4

If an oil-filled capacitor has a terminal with an identification mark, this mark indicates that the terminal is connected to the plate that is located ? the outer metal container or can.

nearer to 5Q19

CEMF ? the applied EMF when current is increasing and ? the applied EMF when current is decreasing.

subtracts from / adds to 1Q11

If a change of one ampere in one second causes one volt to be induced, you have ? of inductance.

one henry 1Q18

The following questions are not included

1Q13 & 24

When current flows in a conductor, a magnetic field is produced. As free electrons move in one direction, their individual magnetic fields ? .

add together 1Q3

The unit of inductance is the ? , and inductance is represented by the letter ? .

henry / L 1Q17

At what percentage is the current after four time constants?

98.1%

As current flow decreases, the magnetic field surrounding the conductor will ? .

Decreases 1Q5

The unit of capacitance is the farad, abbreviated ? . a. capacitor b. C c. is not d. F e coulomb

F 4Q3

When a capacitor of one farad is connected to a source of one volt, its charge is one ? .

coulomb 4Q3

If the electrical stress across a capacitor is excessive, it will be destroyed. Therefore, the ? rating of capacitors should never be exceeded.

voltage 5Q9

A 120-VAC source is applied to a capacitor. The ? rating on the capacitor would have to be a minimum of 170 volts DCWV.

voltage 5Q10

What is the schematic symbol of a capacitor?

---I C---- 4Q8

One picofarad is one farad times 10^?

-12 4Q7

At what percentage is the current after five time constants?

100%

One picofarad in decimal form is written as ? F.

.000 000 000 001 4Q5

Calculate the amount of time it will take for the current to reach its maximum value in a circuit having 125 millihenries of inductance and 50 ohms of resistance.

.0125 seconds Note: T = L / R = 0.125 / 50 = 0.0025 I_MAX_ = 5T = 5 * 0.0025 = .0125 1Q23

One microfarad in decimal form is ? and may be abbreviated ? .

0.000 001 F / 1 µF 4Q4

Counter Electromotive Force is sometimes called back EMF, and CEMF is ? out-of-phase with the applied voltage.

180 degrees 1Q10

How long will it take for a 50 µF capacitor to fully charge if it is in a series circuit with a 100 KΩ resistor?

25 seconds note: t = R * C =100,000 * .000 005 = 5 seconds 5 time constants 5 * 5 = 25 4Q24

The symbol for inductance is ?.

L 3Q3

At what percentage is the current after one time constant when the circuit is first energized?

63.2% 1Q16

One time constant is the amount of time required to charge a capacitor to ? of the amount left to reach its full charge.

63.2% 4Q20

During each time constant, the curve will see a change equal to ? of the amount of voltage left to reach the fully charged state.

63.2% 5Q15

What is the formula for determining counter EMF (induced voltage of a coil)

CEMF = - L * <(delta of I) / (delta of T)>

A(n) ? will not hold its charge indefinitely. a. capacitor b. C c. is not d. F e coulomb

Capacitor 4Q3

When a conductor moves through a stationary magnetic field an EMF is induced, but when the magnetic field moves and the conductor remains stationary no EMF is induced.

False 1Q6

True or False Two conductors feeding a load would not have capacitance.

False 4Q2

True or False Capacitors charge at a slower rate than they discharge

False 5Q16

True or False A charged capacitor has a voltage potential across it. The plate with a deficiency of electrons is the negative plate.

False 5Q6

True or False Electrons flow through a capacitor.

False Note: Electrons do not flow through a capacitor. The dielectric between the plates prevents the electrons from flowing through the capacitor; the electrons flow from one conductive plate to the other conductive plate through the circuitry connected to the capacitor's two terminals. 4Q14

True or False The type of dielectric used has no effect on a capacitor.

False Note: The type of dielectric is a factor in determining the amount of capacitance a capacitor will have. 4Q18

As the current passing through a coil increases, the magnetic field around the coil will ? .

Increase 1Q5

? capacitors can be used in either AC or DC circuits.

Non-polarized 5Q11

Inductive reactance is measured in ?

Ohms 3Q3

? capacitors are often used in motor circuits.

Oil-filled non-polarized. 5Q12

In a DC circuit, what limits current flow?

The resistance of the circuit. 3Q1

The symbol for inductive reactance is ?.

X_L_ 3Q3

Give the formula used to calculate inductive reactance.

X_L_ = 2πFL 3Q4

In high frequency applications, ? inductors are used because of eddy current loss and hysteresis loss in the core material.

air core Note: Remember from earlier chapters, that some core materials such as soft iron are affected when used at higher frequencies. The eddy current losses and hysteresis loss make soft iron a poor choice for use in high frequency applications. 1Q19

? is the letter designation for capacitance. a. capacitor b. C c. is not d. F e coulomb

b. C 4Q3

The physical structure of a(n) ? consists of two conducting surfaces separated by an insulating material.

captacitor

The dielectric in the reference text table with the ? constant is ceramic with a dielectric constant of up to 7,500.

highest 5Q12

What is the opposition to current flow in an AC circuit caused by an inductor called?

inductive resistance 3Q2

Inductance is ? proportional to the length of the core used.

inversely 1Q21

One farad ? a practical unit of capacitance. a. capacitor b. C c. is not d. F e coulomb f. is

is not 4Q3

Whenever current flows through a conductor, a ? is created around the conductor.

magnetic field 1Q1

In a capacitive circuit, the current will ? the voltage by ? .

lead / 90 degrees 4Q17

The flow of electrons through the insulating material of a capacitor is called ? .

leakage 5Q7

A capacitor has the same area of plates and the same distance between the plates. The capacitance will be ? if air is used instead of insulating oil.

lower 4Q19

What is the equation to find the time constant for a resistive-capacitive circuit.

t = R * C 4Q23