Exam 1: Unit 1-7 Delmar's Textbook of electricity Flashcards
Direct current is described as ____
unidirectional
Current that flows in only one direction is referred to as ____ current
direct current
Current that flows in both directions is referred to as ___ current
alternating current
The Greeks were the first to discover electricity about __ years ago.
2500
Objects charged with the same type of charge will push each other away. This is referred to as ___
repulsion
Objects charged with different type of charges will draw toward each other. This is referred to as ___
attraction
An element cannot be chemically subdivided into other elements. The smallest part of an element is ___
an atom
The three principle parts of an atom are the ___
electron, neutron and proton
The part of an atom that has a positive charge is the ___
proton
The part of an atom that has a negative charge is the___
electron
The part of an atom that has no charge is the ___
neutron
The nucleus of an atom contains ___
neutrons and protons
The atomic number of an element is the number of __ in the nucleus
protons
The law of charges states that like charges ___ and opposite charges ___
repel, attract
The valence shell of an atom is the ___
outer
Valence electrons are contained in the ___ shell.
outer
A semiconductor contains ___ valence electrons.
four
What is the term for an amount of charge equal to 6.25 x 10^18 electrons?
coulomb
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
Coulumbs
The ___ is equal to one coulomb per second
amprere
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.
less than
A complete circuit is often referred to as a ___ circuit
closed
A ___ circuit generally occurs when the conductors leading from and back to the power source become connected.
short
___ is also referred to as electromotive force. (EMF)
voltage
The unit of electrical “pressure” that causes current to flow is called the ___
volt
Opposition to the current flow is called ___
resistance
An opposition to current flow that occurs in aleternating currents is called ___
impedance
The ___ is used to measure electrical power being used in a circuit
watt
An electrical device is listed as 3,000 watts. Approximately how many horsepower is this?
4- 1 horsepower= 746 watts
The statement, “in a DC circuit, the current is directly proportional to voltage and inversely porportional to resistance” is known as ___ law.
Ohm’s
An electrical circuit has a voltage of 50 V and a resistance of 5 ohms. What is the value of the current?
10A
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
A static electric charge is an electric charge which __ moving
is not
Insulators are the only materials that can hold ___ stationary.
electrons
Electrostatic charges occur on ___
insulators
The current flow that occurs within a lightening bolt flows ___
negative to positive
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
If a thunder cloud has a positive charge, the current in the lightning bolt will flow from the___
ground to the cloud
The lightning protection device that does not connect directly to the object to be protected is called the lightning ___
arrestor
If you walk across a carpet, touch the doorknob and get a shock, the shock was the result of a ___ static charge.
nuisance
The static charge sometimes used during spray painting is called a ___ static charge
useful
Selenium is a ___
semiconductor
The semiconductor material used as a coating on copy machine drums is ___
selenium
The static charge that accumulates on clothes in a dryer is a ___ charge
nuisance
Lodestrone is a name for a naturally occuring magnetic material that is also known as___
magnetite
The angular difference between true north and magnetic north is known as the angle of ___
declination
Man-made permanent magnets retain their magnetism ___ than natural magnets.
Longer
Magnetism can be explained in terms of ___ spin patterns.
electron
The regions formed in the molecular structure of magnetic metals is sometimes called magnetic___
domains
Magnetic lines of force are called___
flux
A basic law of magnetism stated that unlike poles ___ and like poles ___
attract, repel
A magnet the produces a magnetic field as long as a current is flowing is called a ___ magnet.
electromagnet
The strength of an electromagnet is primarily proportional to its ___
ampere-turns
The measure of a material’s ability to be magnetized is called ___
permeability
The measure of a material’s resistance to magnetism is __
reluctance
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
The amount of magnetism left in a material after the magnetizing force has stopped is called
residual magnetism
In the English system of measure, magnetic strength is measured in a term called ___
flux density
In the English system, the total force producing a magnetic field is the
magnetomotive
In a ___ circuit, there is little resistance and a large amount of current flows
short circuit
___ 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
Resistors that only have one ohmic value are called ___ resistors
fixed resistors
A ___ resistor is made from a compound of carbon graphite and resin bonding material
composition carbon
The ___ of a resistor indicates the plus and minus limits of a resistor’s ohmic value
tolerance
A ___ resistor is made by combining metal with glass and then applying it to a ceramic base as a thick film
metal glaze
A ___ resistor is made by applying a film of carbon to a ceramic rod
carbon film
A ___ resistor is made by winding a piece of resistive wire around a ceramic core
wire-wound
What does the fourth band of color on a resistor indicate
tolerance
A resistor has color bands of brown, black, red and silver. What is the resistance and tolerance of the resistor?
1000 ohms, 10%
A resistor has color bands of red, violet, brown and gold. What is the resistance and tolerance of the resistor?
270 ohms, 5%
True/False: All insulators perform equally well under dry, damp or wet conditions.
False
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
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
True/False: When a conductor becomes heated the value of resistance decreases
False
a circuit that has only one path for the current to flow is a ___ circuit
series
When a circuit has only one path, the ___ is the same at any point
current
A device that is designed to open and disconnect a circuit in the event of excessive current is a ___
fuse
___ is the force that pushes the electrons through a resistance
voltage
The amount of ___ across a resistor is proprtional to its resistance
voltage drop
The total amount of resistance to current flow in a series cicuit is equal to the ___ of the resistance in that circuit
sum
The current, voltage, power and resistance in a series circuit can be found by using ___ law
Ohm’s
A series cicuit has a total resistance of 180 ohms and an applied voltage of 120V. What is the current flow?
.666A
A series cicuit has a total resistance of 240 ohms and a current flow of 4 A. What is the applied voltage?
960V
The two resistors in a series circuit have voltages of 25V and 60V. The applied voltage is___
85V
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
A series cicuit has two resistors. The resistors dissipate 10W and 15W. What is the total power dissipation of the circuit?
25W
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
A voltage __ is ised to proved different voltages between certain points in a circuit
divider
A ___ must never be connected to a circuit when the circuit power is turned on
ohmeter
The National Electric Code* ___ contains tables dealing with conductors for general wiring.
NEC 310
The National Electrical Code* the current carrying abilities on conductors is called
ampacities
The ambient air temperature considered in relation to a conductor ampacity is the temperature of the___
surrounding air
The noninductive covering around a wire is the ___
insulation
The insulation used on conductors cannot operate in all possible temperatures. The highest allowable temperature is called the ___ temperature
maximum operating temperature
The ampacities listed in table 319.16 are based on an ambient temperature of__
86 degrees
If there are more than ___ conductors in a raceway, the ampacity of the conductors must be derated.
three
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
the unit circular mill is equal to the __
diameter of the wire in mils squared
A wire that has a diameter of 162 mils has an area of ___circular mils
26,244
The longer the conductor, the more ___ it will have
resistance
Materials that increase their resistance with an increase in temperature have a ___ coeficient of temp
positive coefficient
In the american Engineers Handbook, the standard temperature of material resistance is ___
20 degrees celsius
When a conductor is very large it may become necessary to connect them in ___
parallel
When a conductor cuts magnetic lines of force, a voltage is induced into the conductor. This principle is called ___
electromagnetic induction
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
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%
The unit of inductance is the ___
henry(H)
The time required for a current in an inductor to reach its full Ohm’s law value is called the ___ time constant
R-L
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
One device used for spike suppression in either direct or alternating current circuits is the ___
metal oxide varistor
