Ch 1 Flashcards
The Law of Attraction and Repulsion of magnets states:
Like poles repel each other and unlike poles attract each other
This is the result of the atomic bonding of two or more atoms
Compounds
What would you use to protect the electrical equipment in a building?
Surge protectors
What will a magnet align itself with if it is hung freely from a piece of string?
Earth’s magnetic field
What keeps electrons from breaking out of their orbit around the nucleus?
Law of electrical charges
When a magnet is hung freely, what do you call the end that is pointing north?
north-seeking pole
What do you call a switch that uses an electromagnetic field to open or close a set of contacts?
Electromagnetic Relay
When atoms of elements combine they produce _____
Compounds
Some crystalline materials produce a small electrical voltage when bending or twisting pressure is applied to them, what is the effect?
Pressure (Piezoelectricity)
Illumination is produced when a source of energy strikes phosphorus materials
Phosphorescent illumination
The conductor that rotates between the stationary magnetic field poles of the stator is called what?
Rotor or armature
What is the maximum let-go threshold for women and men?
10mA and 16 mA
What is the only naturally occurring magnet?
Lodestone
When energy is applied to valence electrons, it is divided evenly among them, how does that affect them?
Fewer valence electrons for a given amount of energy means each valence electron receives more available energy.
What causes the armature of a dc motor to rotate?
The repelling forces of similar magnetic polarities and the attracting force of opposing polarities.
How many shells are around the nucleus of an atom where electrons orbit?
7
This is the process where heat is applied to dissimilar metals that are joined together to produce about 5 to 30 thousandths of a volt.
Thermoelectric effect
(T/F) A magnet will affect a compass?
True
What forces the rotor to rotate in a generator?
Prime Mover
What materials make up permanent and temporary magnets?
Hard Steel & Soft Iron
What do you call the stationary magnetic field around a dc motor?
Stator
Compounds can change the _____ _______ of the individual atoms
electrical characteristics
What does a clamp-on AC ammeter detect?
The rising and falling and falling of the magnetic field around the conductor.
What dictates the distance an arc can jump?
Voltage & Dielectric
(T/F) Lightning strikes both metallic and nonmetallic objects with the same frequency?
True
(T/F) Both AC and DC electromagnetic fields are used to operate motors and relays
True
(T/F) Ions can be positively or negatively charged?
True
The smallest particle of a compound is called what?
Molecule
(T/F) You cannot have normally open and normally closed contacts in a single relay?
False
What is lightening protection intended to protect?
The building itself, not the electrical equipment.
What happens when you demagnetize a magnet?
The molecules are disarranged to their original orientations
What is the condition in which an atoms valence shell is completely filled?
Chemical Stability
Which direction do the lines of force on electrons and protons go?
Electrons - In : Protons - Out
This has a moving coil, a dc battery supply, and is connected in series with he resistor being measured.
Ohmmeter
Illumination is produces when a high-resistance tungsten metal filament is heated in a vacuum glass lamp
Incandescent
The closer the flux lines and the greater number of flux lines means what?
The stronger the magnetic field
What device would you use to measure very high resistance and what is the voltage range it would be used in?
Megohmmeter, (500-1000V)
Once enough energy has been applied to force an electron out of it orbit, where will it go?
Towards a positive charge or away from a negative charge
Why is copper a better conductor than aluminum?
It has less valence electrons
The complete path electrons take is called ______
electrical circuit
How many valence electrons do insulator atoms have?
6-8
What is the outermost shell of an atom called?
Valence
In DC ammeters, actual circuit current is connected in _______ with the meter coil?
Series
How does a voltmeter work? (analog)
There is a coil around a soft iron bar and when current flows through the coil it creates an electromagnetic field which exerts force on the iron bar and moves it.
What is it called when there is an excess of, or a deficiency of, electrons between objects that have been separated?
Static Charge
What do you call the movement of electrons for the purpose of transferring energy to perform useful functions?
Electricity
(T/F) Flux lines travel North to South and can cross
False
What is a voltmeter is used to measure?
AC / DC voltage
When you magnetize and iron bar, what happens that makes it become magnetic?
The molecules align in the same direction
If you are measuring a current larger than 10 mA, with a directly connected meter what is often required? How is it installed?
A resistor, called a “shunt” ; In parallel with the meter movements coil.
How and where is most of the electrical energy utilized today created?
Power plants, they rotate a magnetic field through a conductor
What happens to electrons when two conductive materials separate?
They go back to their original surface before the separation is complete
The movement of electrons from their atoms is the basis of_____
Current flow (electricity)
Everything on earth that occupies space and has weight is called what?
Matter
(T/F) A bar of soft iron makes a stronger magnet than hard steel?
True
Air terminals are often called what?
Lightening rods
What is the law of electrical charges?
Particles with like charges repel each other and particles with unlike charges attract
A DC generator requires the magnetic field of the stationary field (stator) to be produced from a _______ or ____ that is always in the same direction.
permanent magnetic : electromagnetic field
Are semiconductor atoms better used for insulating or conducting?
They can be used for both
This is a term that refers to the relative ease at which material can be magnetized
Permeability
This process builds up layers of metal on one surface and removes the same metal from another by the chemical action of an electric current in a solution
Electroplating
Conductive materials are made up of materials that have how many valence electrons?
1-3
The magnetic field of a magnet is visualized as what?
Flux lines
The attracting and repelling force of subatomic particles is sometimes referred to as what?
Electrostatic Field
(T/F) DC current is used to produce an alternating electromagnetic field that is necessary for the operation of transformers
False
Materials that are good conductors of magnetic force are called _____
Magnetic Materials
Power source consisting of voltaic cells combined in a series arrangement
Battery
What is the maximum number of electrons allowed in valence shell?
8
If a magnet loses its magnetism quickly, what is it called?
Temporary magnet
What dictates the temperature of an arc?
Amperage
______ Means that the contacts are closed when the relay is not energized, but open when the relay is energized
Normally Closed
______ Means that the contacts are open when power is not applied to the coil, but the contacts close when power is applied
Normally Open
What do you call charged atoms?
Ions
Photoelectricity works on the principle that ____
light (photons) striking a semiconducting plate causes it to release electrons to another semiconducting plate
An electric fault can cause a severe arc blast with temperature up to how high?
30,000 degree F
How many shells are around an atom?
7
Which electrons are more susceptible to being separated from their atomic structure and why?
The electrons furthest away because their attraction becomes weaker the farther away their orbit is from the nucleus.
Light is produced when an electric arc flows through a charged gas lamp
Electric Discharge Lighting
Illumination results from the combination of electroluminescence and phosphorescence when electric current flows through a charged gas or vapor causing the emission of invisible, ultraviolet radiation, which strikes a phosphorescent coating.
Fluorescent lighting
What would you do to prevent corrosion on low voltage electronic circuitry conductors?
Apply gold or silver plating to the copper cable terminals
In order for current to flow from the power source through the appliance / equipment and back to the power source the current flow path must be _______
conductive
Semiconductor atoms contain how many valence electrons?
4-5
Electric current can produce light in these four different ways:
Incandescent, Electric Discharge, Phosphorescent, and Fluorescent
What are the principles in which electric motors work?
Attracting and repelling forces of a magnetic field
How does an atom become chemically stable?
Atomic bonding
What subatomic particle is the lightest?
Electrons
This converts gaseous fuel, such as natural gas or propane, into electrical energy
Fuel Cells
Steel and ____ metals have magnetic properties (excepts stainless steel)
ferrous
What do you use to protect buildings and structures from lightening discharges?
Air terminals (lightening rods)
What are 5 ways to force electrons to move?
Heat, Pressure, Light, Magnetism, and Chemical Activity
DC voltmeters are connected in ______ with the circuit and measure the _________ of potential between the two test leads.
Parallel : Difference
In a holding relay, what makes it safe?
One the relay is de-energized, the power to the equipment will be removed and the only way to re-energize the circuit is to push the start button.
An electric shock from as little as ____ volts ac for as little as ______ can disrupt the heart’s electrical circuitry causing it to go into ventricular fibrillation
30V , One second
What is the generally accepted theory about what magnets are made of?
They are made up of a very large number of small magnets. If molecules in an iron-based metal are pointing in the same direction, the magnetic fields add together.
What happens if you connect a dc ammeter in parallel with the load?
The meter will operate at the source voltage and the current flowing through it will be extremely high. It will most likely destroy the meter if it doesn’t have internal protection.
How does magnetism (magneto electricity) work?
It isn’t the force of the magnetic field moving through a conductor that produces electricity, it is the relative motion of the magnetic field to the electrons within the conductor. The magnetic field pulls or pushes electrons through the circuit.
What do you call the attractive force between a proton and electron?
Electrostatic field
What do you call a high-current discharge that temporarily neutralizes the positive and negative charges between objects?
Stroke
Are high-voltage cells in lightning usually positively or negatively charged?
Negatively
What are two ways to magnetize an iron bar?
Electric current or magnetic stroking
Term that refers to how much magnetic materials can retain magnetism?
Retentativity
This is used for extremely accurate resistance measurements
The Wheatstone Bridge
How does an electric motor work?
A conductor that has current flowing through it creates an electromagnetic field around the conductor and is placed inside a stationary magnetic field of a dc motor which causes the free moving conductor to move
What is the principle behind appliances such as toasters and ovens?
Heat (resistance) electricity is sent through a high resistance heating element that produces heat as electrons flow through the circuit.
What are the three methods used to demagnetize a magnet?
Hard blow, heat, or ac field
What do you call the discharge of high voltage cells within clouds to each other, the earth, and sometimes space?
Lightning
In a voltmeter, what would cause the iron bar to go farther into the coil?
The greater the voltage, the greater to current flow through the meter, the greater the magnetic field is produced which pulls the iron bar is drawn in.
What does an ohmmeter measure?
Resistance or opposition to the current flow of a circuit or component.
Ionized paths that zigzag toward earth
Stepped Leaders
On an AC generator, which of these is stationary and which of these is revolving: Magnetic Field & AC Winding.
Magnetic field is revolving and the AC Windings are stationary.
How does a generator operate?
Prime Mover forces the armature to rotate while it is subjected to the static magnetic field of the stator which forces electrons in the conductor to move
How high of voltage & current can a lightening bolt have?
30 million volts / 20 thousand amps
Using electric current to alter the effects of chemical bonding so as to separate or encourage the formation of new compounds is the basis of ______ & ______
Electroplating and Electrolysis
An atom contains how many subatomic particles and what are they?
3, Electrons : Protons : Neutrons
