Exam 1: Unit 1-7 Delmar's Textbook of electricity Flashcards
1
Q
Direct current is described as ____
A
unidirectional
2
Q
Current that flows in only one direction is referred to as ____ current
A
direct current
3
Q
Current that flows in both directions is referred to as ___ current
A
alternating current
4
Q
The Greeks were the first to discover electricity about __ years ago.
A
2500
5
Q
Objects charged with the same type of charge will push each other away. This is referred to as ___
A
repulsion
6
Q
Objects charged with different type of charges will draw toward each other. This is referred to as ___
A
attraction
7
Q
An element cannot be chemically subdivided into other elements. The smallest part of an element is ___
A
an atom
8
Q
The three principle parts of an atom are the ___
A
electron, neutron and proton
9
Q
The part of an atom that has a positive charge is the ___
A
proton
10
Q
The part of an atom that has a negative charge is the___
A
electron
11
Q
The part of an atom that has no charge is the ___
A
neutron
12
Q
The nucleus of an atom contains ___
A
neutrons and protons
13
Q
The atomic number of an element is the number of __ in the nucleus
A
protons
14
Q
The law of charges states that like charges ___ and opposite charges ___
A
repel, attract
15
Q
The valence shell of an atom is the ___
A
outer
16
Q
Valence electrons are contained in the ___ shell.
A
outer
17
Q
A semiconductor contains ___ valence electrons.
A
four
18
Q
What is the term for an amount of charge equal to 6.25 x 10^18 electrons?
A
coulomb
19
Q
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. This is ___ law
A
Coulumbs
20
Q
The ___ is equal to one coulomb per second
A
amprere
21
Q
The velocity of AC through a conductor is __ the speed of light because magnetic fields travel more slowly in material dielectrics than they do through free air.
A
less than
22
Q
A complete circuit is often referred to as a ___ circuit
A
closed
23
Q
A ___ circuit generally occurs when the conductors leading from and back to the power source become connected.
A
short
24
Q
___ is also referred to as electromotive force. (EMF)
A
voltage
25
The unit of electrical "pressure" that causes current to flow is called the ___
volt
26
Opposition to the current flow is called ___
resistance
27
An opposition to current flow that occurs in aleternating currents is called ___
impedance
28
The ___ is used to measure electrical power being used in a circuit
watt
29
An electrical device is listed as 3,000 watts. Approximately how many horsepower is this?
4- 1 horsepower= 746 watts
30
The statement, "in a DC circuit, the current is directly proportional to voltage and inversely porportional to resistance" is known as ___ law.
Ohm's
31
An electrical circuit has a voltage of 50 V and a resistance of 5 ohms. What is the value of the current?
10A
32
An electrical circuit has a resistance of 20 ohms. The current is measured to be 6A. How many volts are applied to the circuit?
120
33
A static electric charge is an electric charge which __ moving
is not
34
Insulators are the only materials that can hold ___ stationary.
electrons
35
Electrostatic charges occur on ___
insulators
36
The current flow that occurs within a lightening bolt flows ___
negative to positive
37
When an object if protected by a lightening ___ is struck by a lightning bolt, it will bleed the lightning discharge to the grond before the protected object can be harmed.
rod
38
If a thunder cloud has a positive charge, the current in the lightning bolt will flow from the___
ground to the cloud
39
The lightning protection device that does not connect directly to the object to be protected is called the lightning ___
arrestor
40
If you walk across a carpet, touch the doorknob and get a shock, the shock was the result of a ___ static charge.
nuisance
41
The static charge sometimes used during spray painting is called a ___ static charge
useful
42
Selenium is a ___
semiconductor
43
The semiconductor material used as a coating on copy machine drums is ___
selenium
44
The static charge that accumulates on clothes in a dryer is a ___ charge
nuisance
45
Lodestrone is a name for a naturally occuring magnetic material that is also known as___
magnetite
46
The angular difference between true north and magnetic north is known as the angle of ___
declination
47
Man-made permanent magnets retain their magnetism ___ than natural magnets.
Longer
48
Magnetism can be explained in terms of ___ spin patterns.
electron
49
The regions formed in the molecular structure of magnetic metals is sometimes called magnetic___
domains
50
Magnetic lines of force are called___
flux
51
A basic law of magnetism stated that unlike poles ___ and like poles ___
attract, repel
52
A magnet the produces a magnetic field as long as a current is flowing is called a ___ magnet.
electromagnet
53
The strength of an electromagnet is primarily proportional to its ___
ampere-turns
54
The measure of a material's ability to be magnetized is called ___
permeability
55
The measure of a material's resistance to magnetism is __
reluctance
56
When a magnetic materials molecules are all lined up, and increase in current flow no longer cause increases in magnetic field strength, the material has reached
saturation
57
The amount of magnetism left in a material after the magnetizing force has stopped is called
residual magnetism
58
In the English system of measure, magnetic strength is measured in a term called ___
flux density
59
In the English system, the total force producing a magnetic field is the
magnetomotive
60
In a ___ circuit, there is little resistance and a large amount of current flows
short circuit
61
___ were used in vacuum-tube circuits many years ago and are still used today in applications involving field-effect transistors (FETs) and multirange voltmeter circuits
voltage dividers
62
Resistors that only have one ohmic value are called ___ resistors
fixed resistors
63
A ___ resistor is made from a compound of carbon graphite and resin bonding material
composition carbon
64
The ___ of a resistor indicates the plus and minus limits of a resistor's ohmic value
tolerance
65
A ___ resistor is made by combining metal with glass and then applying it to a ceramic base as a thick film
metal glaze
66
A ___ resistor is made by applying a film of carbon to a ceramic rod
carbon film
67
A ___ resistor is made by winding a piece of resistive wire around a ceramic core
wire-wound
68
What does the fourth band of color on a resistor indicate
tolerance
69
A resistor has color bands of brown, black, red and silver. What is the resistance and tolerance of the resistor?
1000 ohms, 10%
70
A resistor has color bands of red, violet, brown and gold. What is the resistance and tolerance of the resistor?
270 ohms, 5%
71
True/False: All insulators perform equally well under dry, damp or wet conditions.
False
72
True/False:The amount of voltage induced into a conductor depends on the turns of wire, the strength of the magnetic field and the speed of cutting action
true
73
True/False: If current is flowing in a circuit containing an inductor and the power switch is opened, the magetic field surrounding the inductor collapses amd induces voltage into the inductor, resulting in a voltage spike
true
74
True/False: When a conductor becomes heated the value of resistance decreases
False
75
a circuit that has only one path for the current to flow is a ___ circuit
series
76
When a circuit has only one path, the ___ is the same at any point
current
77
A device that is designed to open and disconnect a circuit in the event of excessive current is a ___
fuse
78
___ is the force that pushes the electrons through a resistance
voltage
79
The amount of ___ across a resistor is proprtional to its resistance
voltage drop
80
The total amount of resistance to current flow in a series cicuit is equal to the ___ of the resistance in that circuit
sum
81
The current, voltage, power and resistance in a series circuit can be found by using ___ law
Ohm's
82
A series cicuit has a total resistance of 180 ohms and an applied voltage of 120V. What is the current flow?
.666A
83
A series cicuit has a total resistance of 240 ohms and a current flow of 4 A. What is the applied voltage?
960V
84
The two resistors in a series circuit have voltages of 25V and 60V. The applied voltage is___
85V
85
A two-resistor series circuit has an applied voltage of 100V. The voltage across one of the resistors is 40V. The voltage across the other resistor is___
60V
86
A series cicuit has two resistors. The resistors dissipate 10W and 15W. What is the total power dissipation of the circuit?
25W
87
A three-resistor circuit has a total power of 25W. Two of the resistors dissipate 10W and 5W respectively. How much power does the third resistor dissipate?
10W
88
A voltage __ is ised to proved different voltages between certain points in a circuit
divider
89
A ___ must never be connected to a circuit when the circuit power is turned on
ohmeter
90
The National Electric Code* ___ contains tables dealing with conductors for general wiring.
NEC 310
91
The National Electrical Code* the current carrying abilities on conductors is called
ampacities
92
The ambient air temperature considered in relation to a conductor ampacity is the temperature of the___
surrounding air
93
The noninductive covering around a wire is the ___
insulation
94
The insulation used on conductors cannot operate in all possible temperatures. The highest allowable temperature is called the ___ temperature
maximum operating temperature
95
The ampacities listed in table 319.16 are based on an ambient temperature of__
86 degrees
96
If there are more than ___ conductors in a raceway, the ampacity of the conductors must be derated.
three
97
There are 6 current carrying conductors in a raceway that is to be installed in an area with an ambient temp of 90 degrees. It is necessar to___
correct for temp and derate
98
the unit circular mill is equal to the __
diameter of the wire in mils squared
99
A wire that has a diameter of 162 mils has an area of ___circular mils
26,244
100
The longer the conductor, the more ___ it will have
resistance
101
Materials that increase their resistance with an increase in temperature have a ___ coeficient of temp
positive coefficient
102
In the american Engineers Handbook, the standard temperature of material resistance is ___
20 degrees celsius
103
When a conductor is very large it may become necessary to connect them in ___
parallel
104
When a conductor cuts magnetic lines of force, a voltage is induced into the conductor. This principle is called ___
electromagnetic induction
105
If a voltage is being induced into a conductor by electromagnetic induction, reversing the direction of motion of the conductor will ___
reverse the polarity of the induced voltage
106
During the period of time called the first time constant of an exponetial curve, the current will rise to about ___ % of its full value
63.2%
107
The unit of inductance is the ___
henry(H)
108
The time required for a current in an inductor to reach its full Ohm's law value is called the ___ time constant
R-L
109
A coil has an inductance of 3H and a wire resistance of 15 ohms. How long will it take for the current to reach its full value?
1 second. L/Rx5
110
One device used for spike suppression in either direct or alternating current circuits is the ___
metal oxide varistor
