• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

Card Range To Study

through

image

Play button

image

Play button

image

Progress

1/125

Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

125 Cards in this Set

  • Front
  • Back
What is matter, and in what three states is it found?
Anything that occupies space and has weight. Solids, liquids, gases.
What is an element?
A substance which cannot be reduced to a simpler substance by chemical means.
What is a compound?
A substance consisting of two or more elements.
What is the difference between a compound and a mixture?
A compound is a chemical combination of elements that cannot be separated by physical means. A
mixture is a physical combination of elements and compounds that are not chemically combined.
What is a molecule?
A chemical combination of two or more atoms.
What are the three types of subatomic particles, and what are their charges?
Electrons-negative, protons-positive, and neutrons-neutral
What is energy of motion called?
Kinetic energy.
How is invisible light changed to visible light in a fluorescent light?
Invisible light photons (ultraviolet) bombard the phosphor atom in the light tube. The phosphor
atoms emit visible light photons.
What determines the valence of an atom?
The number of electrons in the outer shell.
What is an ion?
An atom with more or less than its normal number of electrons.
What determines whether a substance is a conductor or an insulator?
The number of valence electrons.
How is a negative charge created in a neutral body?
Through the accumulation of excess electrons.
How are static charges created?
By friction.
What is the electrical charge of an atom which contains 8 protons and 11 electrons?
Negative.
What is the relationship between charged bodies?
Like charges repel, and unlike charges attract with a force directly proportional to the product of
their charges and inversely proportional to the square of the distance between them.
What is an electrostatic field?
The space between and around charged bodies.
In what direction are electrostatic lines of force drawn?
Leaving positive, entering negative.
What are some examples of electrical equipment which use magnetism?
Motors, generators, speakers, computers, televisions, tape recorders, and many others.
What are magnetic materials?
Those materials that are attracted by magnets and have the ability to become magnetized.
What characteristics do all ferromagnetic materials have in common?
The relative ease with which they are magnetized.
What type of magnetic material should be used to make a temporary magnet?
A material that exhibits low reluctance and high permeability, such as iron or soft steel.
What is retentivity?
The ability of a material to retain magnetism.
How does the law of magnetic poles relate to the law of electric charges?
They are very similar; like charges repel, unlike charges attract, like poles repel —unlike poles
attract.
A compass is located at the geographical North Pole. In which direction would its needle point?
To the magnetic north pole.
Using Weber’s molecular theory of magnetism, describe the polarity of the magnetic poles
produced by stroking a magnetic material from right to left with the south pole of a magnet.
South pole at the right, north pole at the left.
What is the difference between the domain theory and Weber’s theory of magnetism?
The domain theory is based upon the electron spin principle; Weber’s theory uses the concept of
tiny molecular magnets.
Refer to figure 1-13. For what purpose would you sprinkle iron filings on the glass plate?
To enable you to "see" the magnetic field.
Refer to figure 1-13. What pattern would be formed if sawdust was sprinkled on the glass instead
of iron filings?
No specific pattern, sawdust is a nonmagnetic material.
What is a magnetic line of force?
An imaginary line used to illustrate magnetic effects.
In what way do magnetic lines of force differ from electrostatic lines of force?
Electrostatic lines of force do not form closed loops.
How should a delicate instrument be protected from a magnetic field?
By shielding or surrounding the instrument with a soft iron case, called a magnetic shield or
screen.
How should bar magnets be stored?
In pairs, with opposite poles together to provide a complete path for magnetic flux.
What is the definition of energy?
The ability to do work.
What type of energy does a rolling stone have?
Kinetic energy.
What kind of energy does the stone have if it is at rest at the top of a hill?
Potential energy.
What term describes voltage or emf?
Difference of potential.
Convert 2.1 kV to volts.
2100 volts.
Express the following in more simple terms. (a) 250,000 volts, (b) 25,000,000 microvolts, (c)
0.001 millivolt.
(a) 250 kV, (b) 25 V, (c) 1 9
A device which supplies a voltage is commonly referred to by what name?
A voltage source.
Name the six methods of producing a voltage.
Friction, pressure, heat, light, chemical action, and magnetism.
The piezoelectric effect is an example of a voltage being produced by what method?
Pressure.
A thermocouple is a device that produces voltage by what method?
Heat.
A battery uses what method to produce a voltage?
Chemical.
A generator uses what method to produce a voltage?
Magnetic.
According to electron theory, an electric current flows from what potential to what potential?
Electron theory assumes that electron flow is from negative to positive.
The effects of directed drift take place at what rate of speed?
The speed of light (186,000 miles per second, 300,000,000 meters per second).
What is the relationship of current to voltage in a circuit?
Current increases as voltage increases.
Convert 350 mA to amperes.
0.35 amperes.
What is the symbol for ohm?
Ohm
When would silver be used as a conductor in preference to copper?
When the need for conductivity is great enough to justify the additional expense.
Which wire has the least resistance? Wire A-copper, 1000 circular mils, 6 inches long. Wire
B-copper, 2000 circular mils, 11 inches long.
Wire B.
Which temperature coefficient indicates a material whose resistance increases as temperature
increases?
Positive.
What term describes a material whose resistance remains relatively constant with changes in
temperature?
Zero temperature coefficient.
What is the unit of conductance and what other term is sometimes used?
The mho (v), siemens.
What is the relationship between conductance and resistance?
They are reciprocals of each other.
What is schematic symbol for a resistor?
zig zag line
What does the wattage rating of a resistor indicate?
Its ability to dissipate heat.
What are the two disadvantages of carbon-type resistors?
1. Change value with age. 2. Limited power capacity.
What type resistor should be used to overcome the disadvantages of the carbon resistor?
The wirewound resistor.
Describe the differences between the rheostat connections and those of the potentiometer.
The rheostat may have two connections, one fixed and one moveable; the potentiometer always has
three connections, one moveable and two fixed.
Which type of variable resistor should you select for controlling a large amount of current?
The rheostat.
A carbon resistor has a resistance of 50 ohms, and a tolerance of 5 percent. What are the colors of
bands one, two, three, and four, respectively?
The bands are green, black, black, and gold.
A carbon resistor has the following color bands: The first band is yellow, followed by violet,
yellow, and silver. What is the ohmic value of the resistor?
470,000 ohms (470 kilohms).
The same resistor mentioned in question 63 has a yellow fifth band. What does this signify?
The resistor’s chance of failure is 0.001 percent for 1000 hours of operation.
A resistor is handed to you for identification with the following color code: the first band is blue,
followed by gray, green, gold, and brown. What is the resistor’s value?
6,800,000 ohms (6.8 megohms), with 5% tolerance, and a 1% reliability level.
What is the purpose of a cell?
A cell is a device that converts chemical energy to electrical energy.
What are the three parts of a cell?
The electrodes, the electrolyte, and the container.
What is the purpose of each of the three parts of a cell?
The electrodes are the current conductors of the cell. The electrolyte is the solution that acts upon
the electrodes. The container holds the electrolyte and provides a means of mounting the
electrodes.
What are the two types of cells?
Primary and secondary.
What is the main difference between the two types of cells?
The secondary cell can be restored to its original condition by an electric current. The primary cell
cannot.
What is electrochemical action?
The process of converting chemical energy into electrical energy.
What is another name for the (a) positive electrode, and the (b) negative electrode?
a) The anode, (b) the cathode.
In the primary cell, why are negative ions attracted to the negative terminal of the cell?
The positive charge caused by electrons leaving the negative electrode attracts the negative ions.
How do electrons get from the negative electrode to the positive electrode?
By current flow through the load.
What causes the negative electrode to be eaten away?
The chemical action between the negative electrode and the electrolyte.
Refer to figure 2-3(B). Why is the sulfuric acid decreasing?
The sulfuric acid is chemically acting upon the anode and cathode which creates a current flow
through the load.
Refer to figure 2-3(D). How is it possible for the sulfuric acid to be increasing?
The charging currents causes the lead sulfate in the anode and cathode to be changed back to lead
peroxide, sponge lead, and sulfuric acid.
Refer to figure 2-3(D). When all the lead sulfate has been converted, what is the condition of the
cell?
Fully charged.
Describe three ways to prevent polarization.
Vent the cell, add a material rich in oxygen, and use a material that will absorb hydrogen.
Describe local action
Current flow in a cell with no external load.
What serves as the cathode of a dry cell?
The zinc container.
Why is a dry cell called a DRY cell?
The electrolyte is not a liquid but is in the form of a paste.
What does the term "shelf life" mean?
The period that a cell can be stored and still be useable.
Why should a mercury cell NOT be shorted?
The danger of explosion.
What factors should be considered when selecting a primary cell for a power source?
Cost, size, ease of replacement, and voltage or current needs.
What are the four basic types of secondary (wet) cells?
Lead-acid, nickel-cadmium (NICAD), silver-zinc, and silver-cadmium.
What are the advantages of a nicad cell over a lead-acid cell?
Can be charged in a shorter time, can deliver a larger amount of power, and stays idle longer.
What type of cell is most commonly used for emergency systems?
Silver-zinc cell.
What three cells use the same electrolyte?
Silver-cadmium, silver-zinc, and nickel-cadmium.
What does the term battery normally refer to?
A voltage source in a single container made from one or more cells.
What are the three ways of combining cells, and what is each used for?
Series, to increase voltage but not current. Parallel, to increase current but not voltage. Series-
Parallel, to increase both current and voltage.
Other than the type of cell used, what is the major difference between the construction of the leadacid
and nicad battery?
The cells in the nicad battery can be replaced.
How is the type of battery most easily determined?
By looking at the nameplate data.
What is the purpose of the hydrometer?
To measure the amount of active ingredient in the electrolyte.
Which electrolyte has more active ingredient? Electrolyte A, specific gravity 1.015? Electrolyte B,
specific gravity 1.125?
Electrolyte B. It is heavier per unit volume.
When should safety precautions pertaining to batteries be observed?
At all times.
How long should a 200 ampere-hour battery be able to deliver 5 amperes?
Forty hours.
Can a battery be recharged by adding more electrolyte?
No, a current must be passed through the battery.
If violent gassing occurs during a battery charge, what action should be taken?
Reduce the charging rate.
Q4. According to Ohm’s law, what happens to circuit current if the applied voltage (a) increases, (b)
decreases?
(a) Current increases (b) Current decreases
According to Ohm’s law, what happens to circuit current if circuit resistance (a) increases, (b)
decreases?
(a) Current decreases (b) Current increases
What is the equation used to find circuit resistance if voltage and current values are known?
R=I/E
What is the term applied to the rate at which a mechanical or electrical force causes motion?
Power.
How can the amount of current be changed in a circuit?
By changing the circuit resistance or the voltage of the power source.
What are the three formulas for electrical power?
P=IxE, P=E2sqxR, P=I2sqxR
Define direct current.
An electrical current which flows in one direction only.
Define alternating current.
An electrical current which is constantly varying in amplitude, and which changes direction at
regular intervals.
What is a disadvantage of a direct-current system with respect to supply voltage?
The dc voltage must be generated at the level required by the load.
What disadvantage of a direct current is due to the resistance of the transmission wires?
The I 2R power loss is excessive.
What kind of electrical current is used in most modern power distribution systems?
Alternating current (ac).
When placed in the vicinity of a current-carrying conductor, the needle of a compass becomes
aligned at what angle to the conductor?
The needle aligns itself at right angles to the conductor.
What is the direction of the magnetic field around a vertical conductor when (a) the current flows
upward and (b) the current flows downward.
(a) clockwise (b) counterclockwise.
The "left-hand rule" for a conductor is used for what purpose
It is used to determine the relation between the direction of the magnetic lines of force around a
conductor and the direction of current through the conductor.
In what direction will the compass needle point when the compass is placed in the magnetic field
surrounding a wire?
The north pole of the compass will point in the direction of the magnetic lines of force.
When two adjacent parallel wires carry current in the same direction, the magnetic field about
one wire has what effect on the magnetic field about the other conductor?
It combines with the other field.
When two adjacent parallel conductors carry current in opposite directions, the magnetic field about
one conductor has what effect on the magnetic field about the other conductor?
It deforms the other field.
What is the shape of the magnetic field that exists around (a) a straight conductor and (b) a coil?
(a) The field consists of concentric circles in a plane perpendicular to the wire (b) the field of each
turn of wire links with the fields of adjacent turns producing a two-pole field similar in shape to
that of a simple bar magnet.
What happens to the two-pole field of a coil when the current through the coil is reversed?
The polarity of the two-pole field reverses.
What rule is used to determine the polarity of a coil when the direction of the electron current flow
in the coil is known?
Use the left-hand rule for coils.
State the rule whose purpose is described in Q14.
Grasp the coil in your left hand, with your fingers "wrapped around" in the direction of electron
flow. The thumb will point toward the north pole.
When a conductor is rotated in a magnetic field, at what points in the cycle is emf (a) at maximum
amplitude and (b) at minimum amplitude?
(a) When the conductors are cutting directly across the magnetic lines of force (at the 90º and
270º points). (b) When the conductors are moving parallel to the magnetic lines of force (at the
0° , 180° , and 360° points).
One cycle is equal to how many degrees of rotation of a conductor in a magnetic field?
360° .
State the left-hand rule used to determine the direction of current in a generator.
Extend your left hand so that your thumb points in the direction of conductor movement, and your
forefinger points in the direction of the magnetic flux (north to south). Now point your middle
finger 90° from the forefinger and it will point in the direction of electron current flow in the
conductor.
How is an ac voltage produced by an ac generator?
Continuous rotation of the conductor through magnetic fines of force produces a series of cycles
of alternating voltage or, in other words, an alternating voltage or a sine wave of voltage.
Define Frequency.
Frequency is the number of complete cycles of alternating voltage or current completed each
second.