Fundamentals of Alternating Current

P = E x I x PF E means I means PF means

E - means volts I - means amps PF - means Power Factors

The power factor for a certain AC circuit is .8. If the voltage is 480 volts and the current is 50 amps, what is the true power used by the circuit? a) 19,200 watts b) 30,000 watts c) 7.68 watts d) 12 watts

a) 19,200 watts P=480 x 50 x .8

What are two ways to increase inductive reactance in an AC circuit? a)Coil a conductor and add a metal core. b)Remove CEMF and add a magnetic field. c)Induce reactive metal and add a coil of wire. d)Reactivate a voltage and reduce the resistance.

a)Coil a conductor and add a metal core.

The middle line on the secondary side of a three-wire single-phase system is: a)called the neutral line. b)connected in a delta pattern. c)never used. d)110 volts.

a)called the neutral line.

Before a capacitor can store energy, it must first be ___________. a)charged b)discharged c)shorted d)grounded

a)charged

Capacitive reactance is measured in ____________. a)ohms b)volts c)current d)amp

a)ohms

When current flowing through a conductor is increasing: a)the magnetic field around the conductor is building up. b)the magnetic field around the conductor is collapsing. c)no voltage is induced. d)there is no magnetic field around the conductor.

a)the magnetic field around the conductor is building up.

Apparent power is the result of multiplying voltage times current in any circuit. a)true b)false

a)true

Capacitance is a physical property of all AC circuits that opposes a change in voltage. a)true b)false

a)true

In a delta-connected system, phase voltage equals line voltage, but phase current does not equal line current. a)true b)false

a)true

True power is the amount of power actually used to do work. a)true b)false

a)true

When a capacitor is fully charged, the source voltage and the voltage across the capacitor are equal in amount, but opposite in polarity. a)true b)false

a)true

When a sine wave is used to represent voltage, voltage below the horizontal line is negative. a)true b)false

a)true

When CEMF opposes the applied voltage in an AC circuit, it has the effect of increasing current. a)True b)False

b)False

_______ is the measure of the opposition to current flow that is created by inductance. a)Inductance creator b)Inductive reactance c)Inductance opposer d)Inductive creator

b)Inductive reactance

The letters used to express effective AC values are a)EAC b)RMS c)RAC d)COW

b)RMS

Positive power is power that _________ useful work. a)does b)does not do c)reacts to d)will do

b)does not do

A dielectric in a capacitor: a)increases the flow of protons to the positive terminal. b)keeps electrons from flowing from one plate to the other. c)aids electrons in their flow from positive to negative. d)decreases the number of electrons on any plate.

b)keeps electrons from flowing from one plate to the other.

The voltage and current sine waves for reactive power are always ____ phase. a)in b)out of c)reacting to the d)creating multi-

b)out of

Whenever voltage and current increase of decrease at different times, they are said to be ________. a)in phase b)out of phase c)three-phased d)two-phased

b)out of phase

In a three-phased system, the current that flows through the coils or resistors is called ________ current. a)line b)phase c)circuit d)resistance

b)phase

The ________ of an AC power sources changes periodically. a)circuitry b)polarity c)magnets d)brushes

b)polarity

The component that changes a two-wire single-phase system into a three-wire single-phase system is a __________. a) capacitor b) regulator c) transformer d) battery

c) transformer

What is capacitive reactance? a)The measure of voltage in a capacitor created by resistance in a circuit. b)The opposition of a resistance in a battery negative output. c)The measure of opposition to current flow created by capacitance. d)The opposition of current in a purely resistance induced circuit.

c)The measure of opposition to current flow created by capacitance.

In a wye-connected three-phase system, phase current and line current are: a)different than a power factor in a resistive circuit. b)equal to line voltage. c)equal to each other. d)equal to phase voltage.

c)equal to each other.

In a purely inductive circuit, ________ is the only current-limiting factor. a)limited current magnets b)circuit inducers c)inductive reactance d)capacitive reactance

c)inductive reactance

Which of the following are two requirements for inducing a voltage? a)magnets and current b)circuits and motion c)magnetic field and conductor d)relative motion and hertz

c)magnetic field and conductor

When a conductor rotating in a magnetic field is cutting through the maximum number of flux lines, a)the conductor stops moving b)no voltage is induced c)maximum voltage is induced d)none of the above

c)maximum voltage is induced

To calculate the line voltage of a wye-connected three-phase system, multiply the phase voltage by _________. a)delta voltage b).707 c).173 d)1.73

d)1.73

Given the following values, calculate true power. E = 110 volts I = 10 amps PF = .5 a)2.2 watts b)220 watts c)2,200 watts d)550 watts

d)550 watts P= 110 x 10 x .5

The number of cycles completed each second by a given AC voltage is called frequency, and is measured in____________. a)frequent cycles b)current and amps c)horizontal waves d)Hertz

d)Hertz

The physical property of all AC circuits that opposes any change in ___________ is called inductance. a)voltage inducer b)voltage flow c)current indicator d)current flow

d)current flow

Capacitance causes _________ and __________ to be out of phase. a)resistance;current b)current;inductance c)voltage;indcutance d)current;voltage

d)current; voltage

The combined effect of resistance, inductance, and capacitance on current flow in an AC circuit is called ___________. a)applied resistors b)reactance c)induction d)impedance

d)impedance