ELEC 2A MIDTERM EXAM
A three-phase generator has each of its windings out-of-phase with each other by _____. 90° 120° 180° 360°
120
Approximately how many horsepower is an electrical device listed as 3,000 watts?
4
Step-down substations reduce the voltage from the high-voltage transmission lines to a primary distribution voltage of _____. 4 kV to 35 kV 50 kV to 60 kV 69 kV to 100 kV over 169 kV
4 kV to 35 kV
A step-up substation located at the generating facilities transforms the 13.80 kV generator output to _____. 13.20 kV 13.80 kV 69 kV or higher none of these
69 kV or higher
The electric utility grounds the primary and secondary neutral conductor to the earth at multiple locations for the purpose of reducing the _____ of the return current path. ac resistance dc resistance a or b none of these
Ac resistance
A common practical use of induction is for _____. motors transformers generators all of these
All of these
One coulomb per second is equal to one _____. ampere ohm volt watt
Ampere
The number of complete waveforms in one second is called the "frequency." Frequency is expressed as "_____" or "cycles per second." degrees a sine wave phase Hertz
Hertz
The unit of resistance to current flow is the _____. ampere ohm volt watt
Ohm
What type of circuit generally occurs when the conductors leading from and back to the power source become connected? short grounded open closed
Short
A simple ac generator consists of a loop of wire rotating between the lines of force between the opposite poles of a magnet. T or F
T
The effective value is equal to the peak value _____. times 0.314 times 1.41 divided by 1.41 times 0.707
Times 0.707
Delmar
Units
What meter is designed to be connected directly across the power source? voltmeter analog meter galvanometers ammeter
Voltmeter
Self-induced voltage opposes the change in current flowing in the conductor. This is called "inductive reactance" and it is abbreviated _____. XL XC Z none of these
XL
A nonsinusoidal waveform is created when _____ loads distort the voltage and current sine wave. linear resistive inductive nonlinear
nonlinear
"_____" describes the steps necessary to determine the effective voltage or current value. Peak Root-mean-square Instantaneous none of these
root mean square
An electric circuit has a resistance of 20 Ω. The current is measured to be 6 A. How many volts are applied to the circuit?
120
The electrical system usually begins at the generating plant that converts energy to _____, three-phase power. 13.20 kV 13.80 kV 69 kV 138 kV
13.80 kV
In a purely inductive circuit, the CEMF waveform is _____ out-of-phase with the applied voltage waveform. 90° 120° 180° 360°
180
The waveform of the CEMF is _____ out-of-phase with the applied voltage. 90° 120° 180° 360°
180
Phase differences are expressed in degrees; one full waveform is equal to _____. 90° 120° 180° 360°
360
Conductor power losses are directly proportional to the length of the conductor and the square of the current. If the current is doubled, the power loss will be increased by _____ percent. 100 200 300 400
400
In an inductive circuit, the CEMF waveform is 90° out-of-phase with the current waveform and 180° out-of-phase with the applied voltage waveform by, making the voltage waveform lead the current waveform by _____. 90° 120° 180° 360°
90
Electrical power is generated and transmitted across long transmission lines to the customer. These conductors have a very low resistance, but because of their length, the conductor _____ losses can be significant. voltage drop power current a and b
A and b
High-voltage transmission lines are usually connected to transmission lines from other generating plants. This is known as a(n) "_____." interconnected system electrical power grid power system a or b
A or b
Power is transferred from the utility's distribution transformer to the customer via the _____. overhead service drop underground service lateral a or b none of these
A or b
Factors that determine the capacitance of a capacitor are the _____ the plates. surface area of distance between dielectric between all of these
All of these
For ac circuits, the ac _____ of a conductor must be taken into consideration. eddy currents skin effect resistance all of these
All of these
The induced voltage in a conductor carrying alternating current opposes the change in current flowing through the conductor. The induced voltage that opposes the current flow is called "_____." CEMF counter-electromotive force back-EMF all of these
All of these
The output voltage of a generator depends upon the _____. number of turns of wire strength of the magnetic field speed at which the coil rotates all of these
All of these
What meter measures resistance? an ammeter an ohmmeter a voltmeter a wattmeter
An ohmmeter
What meter measures an amount of voltage during a period of time and produces a two-dimensional image? a Wheatstone bridge a bridge circuit an oscilloscope a low impedance voltage tester
An oscilloscope
A test meter that uses a scale and pointer to indicate values is a(n) _____ meter. analog digital
Analog
Distribution transformers reduce the primary distribution voltage to secondary distribution voltage, such as _____. 120/208V 120/240V 277/480V any of these
Any of these
Self-induced voltage is 180° out-of-phase with the _____. When the applied voltage is at its maximum in one direction, the induced voltage is at its maximum in the opposite direction. applied current applied voltage induced voltage induced current
Applied voltage
"_______" is the property of an electrical circuit that enables it to store electrical energy by the means of an electric field and to release this energy at a later time Capacitance Induction Self-induction None of these
Capacitance
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. induced charged discharged shorted
Charged
A complete circuit is often referred to as a(n) _____ circuit. closed open shorted grounded
Closed
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 insulating open all of these
Conductive
What law states that the force of electrostatic attraction or repulsion is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them? Ampere's Law Coulomb's Law Ohm's Law Volt's Law
Coulomb's Law
Phase differences are expressed in _____. sine waves phases Hertz degrees
Degrees
A half-wave rectifier can be used to convert ac voltage into dc voltage to continuously charge a capacitor. T or F
F
A waveform image is used to display the level and direction of current, but not voltage. T or F
F
Conductor resistance is directly proportional to the conductor's length and cross-sectional area. T or F
F
Eddy currents are small independent currents induced within the conductor because of direct current. T or F
F
To prevent fires and electric shock, the NEC specifies that neutral current can flow on metal parts of the electrical system. T or F
F
What standard prefix in engineering notation indicates multiplication by 1,000,000,000? kilo (K) tera (T) giga (G) mega (M)
Giga
The neutral conductor is also referred to as the _____ conductor. hot grounded short safety
Grounded
A voltmeter has a very _____ resistance connected in series with the meter movement. low high
High
Because of the earth's _____ resistance to current flow, it cannot be used for the purpose of clearing a line-to-case ground fault. low high variable unpredictable
High
The series ohmmeter is used to measure _____ values of resistance. low high
High
In a purely resistive ac circuit, the current and voltage are _____. This means that they both reach their zero and peak values at the same time. in-phase out-of-phase a or b none of these
In-phase
The most effective way to reduce conductor voltage drop and power loss is to lower the current flowing through the conductors. This is accomplished by _____ the transmission voltage. reducing applying increasing none of these
Increasing
The movement of electrons caused by an external magnetic field is called "_____ current," and the associated potential that is established is called "_____ voltage." circuit applied induced none of these
Induced
When the current waveform finishes before the voltage waveform, the voltage "_____" the current waveform. leads lags is in-phase with none of these
Lags
If the voltage waveform finishes before the current waveform, the voltage is said to "_____" the current waveform. lead lag be in-phase with none of these
Lead
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° lag the applied voltage by 90° lead the applied voltage by 180° lag the applied voltage by 180°
Lead the applied voltage by 90
The direction of the overall magnetic field around the conductor follows the _____ rule, based on the Electron Current Flow Theory. left-hand right-hand law of attraction none of these
Left-hand
Metal parts of the electric utility equipment are bonded to the utility neutral to provide a _____ path to the power source to assist in clearing a line-to-case fault. high-resistive low-impedance ground none of these
Low-impedance
In order to induce voltage, relative motion is required between a conductor and a _____ field. This is the basis of the generator and transformer. voltage current magnetic none of these
Magnetic
A(n) _____ ammeter operates on more than one range by connecting the meter movement to different shunts. full scale single range multirange omnirange
Multirange
The voltage drop over a conductor is directly proportional to the _____ of the conductor. area circular mils length none of these
None of these
The combination of alternating-current and direct-current waveforms results in a _____ waveform. nonsinusoidal nonsymmetrical sine any of these
Nonsymmetrical
What meter must NEVER be connected to a circuit when the circuit power is turned on? an ammeter a voltmeter an ohmmeter a wattmeter
Ohmmeter
"_____" is the maximum value that ac current or voltage reaches, both for positive and negative polarity. Peak Root-mean-square Instantaneous none of these
Peak
The multipoint grounded neutral is intended to help reduce the _____ utility neutral voltage drop, assist in clearing line-to-neutral/ground utility faults, and to reduce elevated line-to-neutral voltage caused by line-to-neutral/ground faults. primary secondary tertiary all of these
Primary
In dc circuits, the only property that affects current and voltage flow is _____. impedance reactance resistance none of these
Resistance
What causes a wire to become warm when current flows through it? amperage resistance voltage divergence
Resistance
As the alternating current through a conductor increases, an expanding and collapsing electromagnetic field through the conductor induces a voltage within the conductor. This is known as "_____ voltage." applied circuit self-induced none of these
Self-induced
An ammeter is connected in _____ with the load to permit the load to limit current flow. parallel series
Series
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 _____. charged discharged induced shorted
Shorted
The _____ wave is a waveform that is symmetrical with positive above and negative below the zero reference level. nonsinusoidal nonsymmetrical sine any of these
Sine
The expanding and collapsing magnetic field within the conductor induces a voltage in the conductors (CEMF) that repels the flowing electrons toward the surface of the conductor. This is called "_____." eddy currents induced voltage impedance skin effect
Skin effect
Alternating current is primarily used because it can be transmitted inexpensively. T or F
T
Because an iron core provides an easy path for magnetic flux, windings with soft iron cores produce a greater self-inductance than windings with air cores. T or F
T
Capacitors are used to start single-phase ac motors and to prevent arcing across the contacts of electric switches. T or F
T
Effective ac voltage or effective ac current is the equivalent value of dc voltage or dc current that would produce the same amount of heat in a resistor. T or F
T
Electrons leaving a power supply are always trying to return to the same power supply; they are not trying to go into the earth. T or F
T
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. T or F
T
In ac generators that produce large quantities of electricity, the conductor coils are stationary and the magnetic field revolves within the coils. T or F
T
Metal parts of premises wiring must be bonded to a low-impedance path designed so that the circuit protection device will quickly open and clear a ground fault. T or F
T
The earth generally has low enough impedance to permit sufficient fault current to return to the source, thereby opening the utility's circuit protection device. T or F
T
The magnitude of self-induced voltage within a winding is directly proportional to the current flow, the winding, and the frequency at which magnetic fields cut through the winding. T or F
T
The movement of electrons themselves does not produce any useful work. It's the effects that the moving electrons have on the loads they flow through that are important. T or F
T
The term "phase" is used to indicate the time or degree relationship between two waveforms, such as voltage-to-current or voltage-to-voltage. T or F
T
The waveform for ac circuits displays the level and direction of the current and voltage for every instant of time for one full revolution of the rotor. T or F
T
When a magnetic field moves through a coil of wire, the lines of force of the magnetic field cause the electrons in the wire to flow in a specific direction. When the magnetic field moves in the opposite direction, electrons in the wire flow in the opposite direction. T or F
T
When alternating current increases, the polarity of the CEMF within the conductor tries to prevent the current from increasing. T or F
T
When alternating current is applied to the primary of a transformer, it induces a voltage in the secondary which causes electrons to leave one end of the transformer's secondary through the load and return over the remaining circuit's conductors to the transformer's secondary. T or F
T
When electrons move, the magnetic fields of the individual electrons combine to produce an overall magnetic field. The greater the current flow, the greater the overall magnetic field around the conductor. T or F
T
When the alternating current decreases, the polarity of the induced voltage within the conductor tries to prevent the current from decreasing. T or F
T
The peak value is equal to the effective value _____. times 0.707 times 1.41 divided by 2 times 0.58
Times 1.41
Distribution feeders transfer the primary distribution voltage to distribution _____ mounted on poles or on the ground next to the building being served. capacitors generators transformers all of these
Transformers
The amount of potential necessary to cause one coulomb to produce one joule of work is a(n) _____. ampere ohm volt watt
Volt
What is another term for electromotive force (EMF)? Amperage Ohmage Voltage Wattage
Voltage
When describing the relationship between voltage and current, the reference waveform is always _____. current resistance voltage none of these
Voltage
What meter measures true power in a circuit? ohmmeter wattmeter voltmeter ammeter
Wattmeter
The opposition offered to the flow of alternating current by a capacitor is called "capacitive reactance," is expressed in ohms, and abbreviated _____. XC XL Z none of these
XC
"_____" is the value of the voltage or current at a moment of time. Peak Root-mean-square Effective Instantaneous
instantaneous