Exam 2 Study Guide chapters 1-5
magnetic lines of force are called
flux
wire-wound resistors are often used because they are to operate at ___________ power levels than other resistors
higher
the three substances that form the natural magnets are
iron, nickel, and cobalt
The valence shell of an atom is the
outer shell
An electrical circuit has a voltage of 50 V and a resistance of 5 ohms. What is the value of current
10 amps
A resistor has color bands of brown, black, red, and silver. what is the resistance and the tolerance of the resistor
1000 ohms, 10%
An electric circuit has a resistance of 20 ohms. the current is measured to be 6 A. How many volts are applied to the circuit.
120 volts
A toaster is listed as 1560 W. When it is plugged into a 120 V circuit and starts to make toast, how many amperes will it draw?
13 amps
The Greeks were the first to discover electricity about
2500 years ago
A resistor has a color bands of red, violet, brown, and gold. what is the resistance and tolerance of the resistor
270 ohms, 5%
An electrical device is listed as 3000 watts. Approximately how many horsepower is this
4
An electric motor is running on 120 V. The current is measured to be 2 A. How many ohms of resistance is the motor
60
Current that flows in both directions is referred to as
Alternating current
Nuisance Static Charges
An unintended build up of static electricity. Happens on car and truck as they move through the air, builds on a person as they walk across the carpet, and occurs is a clothes dryer. Mostly on man-made materials.
The lightning protection device that does not connect directly to the object to be protected is called the lightning
Arrestor
An element cannot be chemically subdivided into other elements. The smaller part of an element is a(n)
Atom
Objects charged with different type of chargers will draw toward each other. This is referred to as
Attraction
Current that flows in one direction is referred to as
Direct. Current
The three principles parts of an atom are the
Electron, neutron, and proton
Insulators are the only materials that can hold
Electrons stationary
24 ohms is a standard value for ten percent tolerance resistors
False
A thundercloud cannot contain both positive and negative electric charges.
False
Current always flow from positive to negative
False
the north pole of a compass needle points in the direction of a south geographic pole
False
the word potentiometer comes from the word production
False
The current flow that occurs within a lightning bolt flows
From negative to positive
If a thundercloud has a positive charge, the current in the lightning bolt will flow from the
Ground to the cloud
The neutral conductor is also referred to as the
Grounded conductor
A static electricity charge is an electric charge which
Is not moving
The velocity of AC through a conductor is
Less than the speed of light because magnetic fields travel more slowly in material dielectrics than they do in free air
The most common method of producing electricity is
Magnetism
The unit of resistance to current flow is
Ohm
A conductor is made from a material that contains between
One and three valence electrons
Bringing a charged test object near the ball of a charged electroscope causes the leaves to move close together. This indicates that the test object charge is the
Opposite polarity as the electroscope charge
When an object protected by lightning - is struck by a lightning bolt, it will bleed the lightning discharge to the ground before the protected object can be harmed
Rod
An insulator is a material contains
Seven or eight valence electrons
A(n) - circuit generally occurs when the conductors leading from and back to the power source become connected.
Short
Magnetic North
The direction a compass needle points (in the northern hemisphere) it's also attracted to the south magnetic pole
An electroscope can be used to determine the polarity of an electrostatic charge
True
Lightning is the result of static charges built up in clouds that contain large amount of moisture.
True
Lightning rods provide an easy path to ground for current
True
The application of static electricity is used during the manufacture of sandpaper
True
The discharging of static electricity in thunder clouds creates lightning bolts
True
The grounding conductor is used to help prevent a shock hazard in the event that the ungrounded, or hot, conductor comes in contact with the case or frame of the appliance
True
Voltage pushes current through a wire, but voltage cannot flow through a wire
True
the value of a resistor can often be determined by the "color code"
True
The unit of electrical pressure that causes current to flow is called the
Volt
What is also referred to as electromotive force (EMF)
Voltage
What is used to measure electrical power being used in a circuit.
Watt
A circuit is open, current
Will not flow
A precipitator is a type of _________________.
air filter
Matter has mass and occupies space
always true
the strength of an electromagnet is primarily proportional to its
ampere-turns
a basic law of magnetism states that unlike poles ____ and like poles_____
attract, repel
Alternating current is described as
bidirectional
electrons can form spin patterns that_______ the magnetic field of the material
cancel
a________ resistor is made by applying a film of carbon to a ceramic rod
carbon film
a magnet that produces a magnetic field as long as current is flowing is called a(n)
electromagnet
The part of an atom that has a negative charge is the
electron
magnetism can be explained in terms of _________ spin patterns
electron
Electrical current is the flow of
electrons
resistors that only have one ohmic value are called
fix resistors
The law of charges states that like chargers- and opposite charges
like chargers repel and opposite charges attract
Man-made permanent magnets retain their magnetism _____ than natural magnets.
longer
lodestone is a name for a naturally occurring magnetic material that is also called
magnetite
in the English system, the total force producing a magnetic field is the
magneto motive force
A_________ resistor is made by applying a film of metal to a ceramic rod in a vacuum
metal film
a ________ resistor operates by moving the wiper arm with a screw of some number of turns
multi turn variable
The nucleus of an atom contains
neutrons and protons
if you walk across a carpet, touch a doorknob and get a shock, the shock was the result of a(n)
nuisance static charge
Valence electrons are contained in the
outer shell
____ do not require any power of force to maintain their field
permanent magnets
the measure of a material's ability to be magnetized is called
permeability
The part of an atom that has a positive charge is the
proton
Opposition to current flow is called
resistance
the semiconductor material used as a coating on copy machine drums is
selenium
selenium is a(n)
semiconductor
in a(n) ________ circuit, there is very little resistance and a large amount of current flows
short
the north magnetic pole of of a compass needle is attracted to the
south magnetic pole of the earth
the _________ of a resistor indicates the plus and minus limits of a resistor's ohmic value
tolerance
what does the fourth band of color on a resistor indicate
tolerance
the static charge sometimes used during spray painting is called a(n)
useful static charge
A _________ resistor is made by winding a piece of resistive wire around a ceramic core
wire-wound
A complete circuit is often referred to as a(n)
Closed circuit
In normal operation, current flows through the hot, grounding, and neutral conductors
False
Matter can exist in only two states: solid and liquid
False
A semiconductor contains
Four valence electrons
Electrostatic charges occur on
Insulators
The statement in a DC circuit, the current is directly proportional to voltage and inversely proportional to resistance is know as
Ohm's law
True North
The direction to the geographic North Pole
The precipitator uses a high voltage DC power supply to provide a set of wires with a positive charge and a set of plates with a
Negative charge
The part of an atom that has no charge is the
Neutron
Useful Static Charges
Static electric charges that are intentionally placed on objects
The grounding pong of a plug should never be cut off or bypassed
True
a _________ resistor is made from a compound of carbon graphite and resin bonding material
composition carbon
the angular difference between true north and magnetic north si known as the angle of
declination
if an object is placed in the field of an strong electromagnet connected to an AC line, the object will be
demagnetized
the regions formed in the molecular structure of magnetic metals is sometimes called magnetic __________
domains
in the English system of measure, magnetic strength is measured in a term called
flux density
a _________ resistor is made by combining metal with glass and then applying it to a ceramic base as thick as film
metal glaze
a variable resistor is also called a
potentiometer
a variable with three terminals is called a
potentiometer
The atomic number of an element is the number of
protons in the nucleus
the measure of a material's resistance to magnetism is
reluctance
Objects charged with the same type of charge will push each other away. This is referred to as
repulsion
the amount of magnetism left in a material after the magnetizing force has stopped is called
residual magnetism
a variable resistors with two terminals is called a
rheostat
when a magnetic material's molecules are all lined up, and increases in current flow no longer cause increases in magnetic field strength, the material has reached
saturation
earth contains magnetic poles
true
Direct current is described as
unidirectional
a resistor whose values can be varied over a range of values is called ___________ resistor
variable
______ were used in vacuum-tube circuits many years ago and are still used today in applications involving field-effect transistors (FETs) and multi range voltmeter circuits
voltage dividers