NCTI Installer Tech/November
List gold, silver, and copper in the order of best conductivity. (List the best conductor first.)
#1 Silver; #2 Copper; #3 Gold
20 milliamperes is the same as ________. (Remember, 1 milliampere = 0.001 ampere.)
0.02 amperes
What are two alternate ways to express 2 megavolts?
2 MV or 2 million volts.
What are two alternate ways to express 4 kilovolts?
4 kV or 4,000 volts.
5 kilovolts is the same as
5 kV.
What are three alternate ways to express 5 µV and 3 mA?
5 microvolts, 5/1,000,000 volt or 0.000005 volt, and 3 milliamperes, 3/1,000 ampere or 0.003 A.
Explain how a basic loudspeaker produces sound.
A basic loudspeaker utilizes both a permanent magnet and an electromagnetic coil to produce sound. Current produced by a sound wave is made to flow through the voice coil. The resultant magnetic field of the coil interacts with the magnetic field of the permanent magnet, which causes the coil to move. The cone to which the coil is attached moves back and forth in relation to the varying current of the original sound, which causes the air around the cone to move, thus producing sound.
hat aspect of an electrical system does a block diagram show?
A block diagram shows the circuits as rectangles (and other shapes) and shows how they relate to one another.
How many electrons are in one coulomb?
A coulomb is equal to 6.28 × 1018 electrons.
How many valence electrons are there in a good conductor?
A good conductor has only one or two valence electrons.
What aspect of an electric circuit does a parts layout show?
A parts layout shows the physical location of the components or devices in a circuit.
Name the three basic parts of every electrical circuit.
A power source, a load, and connecting conductors comprise every electrical circuit, when viewed in its basic form.
What are the three basic elements of an electrical circuit?
A power source, a load, and the connecting conductors.
What aspect of an electric circuit does a schematic diagram show?
A schematic diagram shows the electrical connections of the components or devices in a circuit.
How many valence electrons are in a semiconductor?
A semiconductor has four valence electrons.
Identify the device normally used to open and close an electrical circuit.
A switch normally opens and closes an electrical circuit.
What will happen to a valence electron that has enough energy added to it?
A valence electron that has enough energy added to it will move away from its atom.
What is the maximum electron capacity of a valence shell?
A valence shell can hold a maximum of eight electrons.
Magnetic poles that are ___________ will ____________ each other when those poles are near each other.
Alike, repel
Flux lines
Always curve around through the body of the magnet to form complete loops.
Define ampere in terms of coulombs.
An ampere is equal to 1 coulomb passing a given point during 1 second.
Why are some materials magnetic and others not?
An atom of magnetic material has more electrons spinning in one direction than in the other; nonmagnetic material has an equal number of electrons spinning in opposite directions.
What is an electromagnet?
An electromagnet is a temporary magnet that is made by applying a potential difference to a wire that is wrapped around a core of magnetic material.
An ______________ has no current flow because a complete path for current flow does not exist.
An open circuit has no current flow because a complete path for current flow does not exist.
What can force electrons to all move in the same direction?
Applying a negative charge to one end of the wire and a positive charge to the other can force electrons to all move in the same direction. The electrons in the wire will travel toward the positive charge as they are directed by the effects of the unlike charges.
Both _____________ and ____________ current flow can damage or destroy devices and appliances in a circuit.
Both insufficient and excessive current flow can damage or destroy devices and appliances in a circuit.
What essential function do conductors in an electrical circuit provide?
Conductors provide a path for current flow from the power source to the load and from the load back to the power source.
Identify the conducting metal used extensively in electrical circuits and give its relative conductance rating.
Copper is used extensively as the conductor in electrical circuits and has a relative conductance rating of 1.
The magnetic field
Created by a straight piece of wire is weaker than that created by forming loops of wire.
Which device do designers install to reduce the damage resulting from an excessive current condition?
Designers install a fuse or similar protective device in a circuit to reduce the damage resulting from an excessive current condition.
The strength of an electromagnetic field is
Determined by the magnitude of the magnetomotive force (mmf).
Define direct current.
Direct current is continuous electron flow in the same direction.
Simplify and solve the equation: If E = IR then what is the formula for finding I?
E/R.
To what basic principle does each axiom adhere?
Each axiom adheres to the basic principle that whatever is done must be done to both sides of the equation.
The recording head of a tape recorder is actually a(an)
Electromagnet.
Electrons in orbits nearest the nucleus contain _________ energy than those in more distant orbits.
Electrons in orbits nearest the nucleus contain less energy than those in more distant orbits.
Define electromotive force (emf).
Emf is the electrical force that motivates electrons to move in a wire.
A permanent-magnet loudspeaker
Has a cone that moves back and forth in relation to the varying current of the original sound.
A semiconductor material
Has four valence electrons.
Elements that are called conductors
Have very few valence electrons.
The left-hand rule for electromagnetism in a wire states that
If you wrap the fingers of your left hand around the wire with your thumb pointing in the direction of the current flow, your fingers will be wrapped in the direction of the magnetic field.
Describe the complete path for electrons moving in an electrical circuit.
In an electrical circuit, electrons move from the negative terminal of the power source, through the load, and back to the positive terminal of the source.
The ampere
Indicates how many coulombs pass a given point during 1 second.
The power source
Is the part of an electrical circuit that provides a difference of potential.
The load
Is the part of the electrical circuit that uses the electrical energy provided by the power source to carry out some desired function.
What would happen if you suspended magnetite by a string and allowed it to swing freely?
Magnetite will always align itself in a north and south direction when you suspend it by a string and allow it to swing freely.
What can manufacturers use to actuate (open or close) a reed switch?
Manufacturers can use a permanent magnet or an electromagnet to provide the magnetic field needed to actuate (open or close) a reed switch.
Why do metals that each have only one valence electron differ in their conductivity?
Metals that each have one valence electron differ in their conductivity because of the way their atoms pack together into a solid structure.
10 to the power of -3 has a metric prefix of ______.
Milli
Moving a quantity or term from one side of the equal sign to the other side and changing its sign is called ______________.
Moving a quantity or term from one side of the equal sign to the other side and changing its sign is called transposing.
Describe a normal current flow in a circuit.
Normal current flow occurs when the circuit operates properly and no circuit components are damaged.
Define a volt in terms of current and resistance.
One volt is the amount of force required to produce a current of 1 ampere through a resistance of 1 Ω.
Why do only the outer electrons leave their orbit shells?
Only outer electrons leave their orbit shells because electrons farthest from the nucleus are more easily freed from their orbits due to a weaker electrostatic force.
What does the term potential difference mean?
Potential difference is the algebraic difference between the electrical individual potentials of two points.
Name the three terms that are used interchangeably to refer to the force that causes current flow.
Potential difference, electromotive force (emf), and voltageare used interchangeably to refer to the force that causes current flow.
A conductor
Provides a path for the current flow from the power source to the load and from the load back to the power source.
Name the two types of electron current flow.
Random drift and directed flow are the two types of electron current flow.
What do scientists believe causes magnetism?
Scientists believe that magnetism results from the spinning action of each electron on its own axis and orbiting around its own nucleus.
List the capacity of each of the first four orbital shells of an atom.
Shell: #1 = 2 electrons; #2 = 8 electrons; #3 = 18 electrons; and #4 = 32 electrons.
The metal that has the greatest conductance is
Silver.
The amount and direction of rotation of the needle pointer in a D'Arsonval meter movement are _______________ (proportional/inversely proportional) to the amount and direction of the applied current.
The amount and direction of rotation of the needle pointer in a D'Arsonval meter movement are proportional to the amount and direction of the applied current.
What is the basic measurement unit of electron current?
The ampere is the basic measurement unit for electron current.
What prevents the electrons that orbit an atom's nucleus at high speeds from breaking away from the nucleus due to centrifugal force?
The attraction between the positive nucleus and the negative electron.
Give an example of a familiar and commonly used power source.
The battery is a familiar and commonly used power source.
Identify a common DC power source.
The battery is probably the most familiar and widely used DC power source.
How does the speed of electric current compare to that of electron travel?
The effective speed of electric current (186,000 miles per second) is much faster than the actual speed of electron travel (a few hundred miles per second).
List the five basic rules that magnetic flux lines follow.
The five basic rules that magnetic flux lines follow are: (1) they have direction or polarity; (2) they always form complete loops; (3) they cannot cross one another; (4) they tend to form the smallest possible loops; (5) they can pass through magnetic and nonmagnetic materials.
Explain the law of attraction and repulsion between two magnets.
The law of attraction and repulsion between two magnets states that like magnetic poles repel each other, while unlike magnetic poles attract each other.
The ____________ is the part of the circuit that uses electrical energy to carry out some desired function.
The load is the device or part of the circuit that uses electrical energy to carry out some desired function.
Describe the pattern arrangement of the magnetic domains in nonmagnetized and magnetized materials.
The magnetic domains in a nonmagnetized material arrange in a random pattern, which causes the effects to cancel, resulting in no magnetic field. Those in a magnetized material align in the same direction, which causes their magnetic fields to add, making the material magnetized.
Does the magnetic field around a wire that is conducting current become stronger or weaker as the distance from the wire increases? Why?
The magnetic field around a current-carrying conductor becomes weaker as the distance from the conductor increases because the flux lines become farther apart.
How do the magnetic fields between two closely spaced parallel wires that are conducting current interact with each other if the current flow in both wires is in the same direction?
The magnetic fields of two closely spaced parallel wires that are conducting current in the same direction will add together because the flux lines will go in the same direction, forming loops around the wires. The flux lines will attract one another, causing the wires to draw together.
What determines the strength of an electromagnetic field and the number of lines of flux in that field?
The magnitude of the magnetomotive force (mmf) determines the strength of an electromagnetic field and the number of lines of flux in that field.
The term voltage normally refers to
The measurement of the difference in potential between two charges.
What causes electrons to be knocked loose and travel randomly from one atom to another?
The movement of atoms in materials that are conductors and the agitation as they collide cause electrons to be knocked loose and travel randomly from one atom to another.
What major factor determines which category a particular element belongs?
The number of electrons in the valence shell determines the element category.
The major factor for determining whether a particular element is a conductor, a semiconductor, or an insulator is
The number of electrons in the valence shell.
What is required to have a balanced (or stable) atom?
The number of electrons must equal the number of protons in order to have a balanced atom.
Why is the overall magnetic field created by forming loops of wire stronger than that created by a straight piece of wire, both having the same current flow?
The overall magnetic field created by forming loops of wire is stronger than that created by a straight piece of wire because the flux lines in a coil of wire are closer together, and thus the majority of the flux lines are concentrated in the center or core of the loops.
What is the potential difference between two negative charges of equal value?
The potential difference between two negative charges of equal value is zero. There is no potential difference.
What is the part of the circuit that provides a difference of potential?
The power source, or voltage supply, provides the difference of potential in a circuit.
The recording head of a tape recorder is actually an ________________ .
The recording head of a tape recorder is actually an electromagnet.
Electric current is actually produced by
The transfer of energy from valence electron to valence electron as a result of applied charges.
What actually produces electric current?
The transfer of energy from valence electron to valence electron, as a result of applied charges, is what actually produces electric current.
Describe the two characteristics of an insulator.
The two characteristics of an insulator are as follows: 1. Its valence shell is almost filled and tends to be fairly stable. 2. It tries to finish filling its valence shell by capturing additional free electrons.
What is the unit used to indicate the strength or size of the potential difference?
The volt is the unit used to indicate the strength or size of the potential difference.
The orbital shell that has a maximum electron capacity of 18 electrons is the ___________ shell.
Third
Name three ways to increase the strength of an electromagnetic field.
Three ways to increase the strength of an electromagnetic field are: (1) increasing the current flow; (2) increasing the number of turns in the coil; and (3) placing an iron core inside the coil, increasing the flux line density.
Describe two methods for creating a magnet.
Two methods for creating a magnet include: (1) stroking a magnetic metal with a magnet; and (2) wrapping wire around a magnetic metal and passing electric current through the wire.
Describe two methods for demagnetizing a magnet.
Two methods for demagnetizing a magnet are vibration and heat.
Explain how to determine the direction of the magnetic field of an electromagnet.
Use the left-hand rule for electromagnetism in a coil to determine the location of an electromagnet's north pole, and thus the direction of its magnetic field. When you wrap the fingers of your left hand around the coil of wire in the direction of current flow, your thumb will point to the electromagnet's north pole. The direction of the magnetic field leaves from the electromagnet's north pole and re-enters at its south pole.
Magnetism
Was discovered when the Greeks noticed that magnetite always aligned itself in a north and south direction.
Define an equation.
We define an equation as a mathematical statement in which two quantities are equal.
Why do we use symbols and diagrams to represent electrical components and circuitry?
We use symbols and diagrams to save time and space in representing electrical components and circuitry.
Which of the following is a true axiom?
When A = C and B = C, then A = B because both are equal to C, which supports the axiom: Quantities equal to the same quantity are equal to each other.
Normal current flow results
When the circuit operates properly and no damage occurs to the circuit components.
In a magnetic material,
Where only some of the magnetic domains are pointing in the same direction, the magnetic field is weaker.
To create an electromagnet,
Wrap a coil of insulated wire around an iron bar and pass an electric current through the wire.
Define alternating current.
ating current is electron flow that periodically changes direction.