NAVEDTRA 14173A NEETS MODULE 1 CHAPTER 3 Flashcards
1
Q
According to Ohm’s law, what happens to circuit current if the applied voltage (a) increases, (b) decreases?
A
(a) Current increases (b) Current decreases
2
Q
According to Ohm’s law, what happens to circuit current if circuit resistance (a) increases, (b) decreases?
A
(a) Current decreases (b) Current increases
3
Q
What is the equation used to find circuit resistance if voltage and current values are known?
A
R = E/I
4
Q
What is the term applied to the rate at which a mechanical or electrical force causes motion?
A
Power.
5
Q
How can the amount of current be changed in a circuit?
A
By changing the circuit resistance or the voltage of the power source.
6
Q
What are the three formulas for electrical power?
A
P = E x I, P = E to the second divided by R, P = I to the second x R
7
Q
What is the current in a circuit with 5 ohms of resistance that uses 180 watts of power?
A
6 amperes.
8
Q
What is the power used in a circuit that has 10 amperes of current through a 10-ohm resistor?
A
1 kilowatt.
9
Q
How much power is converted by a 1-horsepower motor in 12 hours?
A
8,952 watt hours or 8.952 kWh.
10
Q
What is the efficiency of the motor if it actually uses 9.5 kWh in 12 hours?
A
942 (rounded to 3 places).
11
Q
A series circuit consisting of three resistors has a current of 3 amps. If R1 = 20 ohms, R2= 60 ohms, and R3 = 80 ohms, what is the (a) total resistance and (b) source voltage of the circuit?
A
(a) . 160 ohms
(b) . 480 volts
12
Q
What is the voltage dropped by each resistor of the circuit described in question?
A series circuit consisting of three resistors has a current of 3 amps. If R1 = 20 ohms, R2= 60 ohms, and R3 = 80 ohms, what is the (a) total resistance and (b) source voltage of the circuit?
A
E1 = 60 volts E2 = 180 volts E3 = 240 volts
13
Q
If the current was increased to 4 amps, what would be the voltage drop across each resistor in the circuit described in question?
What is the voltage dropped by each resistor of the circuit described in question?
A series circuit consisting of three resistors has a current of 3 amps. If R1 = 20 ohms, R2= 60 ohms, and R3 = 80 ohms, what is the (a) total resistance and (b) source voltage of the circuit?
A
E1 = 80 volts E2 = 240 volts E3 = 320 volts
14
Q
What would have to be done to the circuit described in question 17 to increase the current to 4 amps?
A
The source voltage would have to be increased to 640 volts.
15
Q
A series circuit consists of two resistors in series. R1 = 25 ohms and R2 = 30 ohms. The circuit current is 6 amps. What is the (a) source voltage, (b) voltage dropped by each resistor, (c) total power, and (d) power used by each resistor?
A
(a) 330 volts
(b) E1 = 150 volts
E2 = 180 volts
(c) 1.98 kilowatts
(d) P1 = 900 watts
P2 = 1.08 kilowatts
16
Q
When using Kirchhoff’s voltage law, how are voltage polarities assigned to the voltage drops across resistors?
A
The point at which current enters the resistor is assigned a negative polarity and the point at which current leaves the resistor is assigned a positive polarity.
17
Q
A circuit has a source voltage of 100 volts and two 50-ohm resistors connected in series. If the reference point for this circuit is placed between the two resistors, what would be the voltage at the reference point?
A
50 volts.
18
Q
If the reference point in question (below) were connected to ground, what would be the voltage level of the reference point?
A circuit has a source voltage of 100 volts and two 50-ohm resistors connected in series. If the reference point for this circuit is placed between the two resistors, what would be the voltage at the reference point?
A
Zero volts.
19
Q
What is an open circuit?
A
A circuit where there is no longer a complete path for current flow.
20
Q
What is a short circuit?
A
An accidental path of low resistance which passes an abnormally high amount of current.
21
Q
Why will a meter indicate more voltage at the battery terminal when the battery is out of a circuit than when the battery is in a circuit?
A
The internal (source) resistance of the battery will drop some of the voltage.
22
Q
What condition gives maximum power transfer from the source to the load?
A
When the load resistance equals the source resistance.
23
Q
A circuit has a source voltage of 25 volts. The source resistance is 1 ohm and the load resistance is 49 ohms. What is the efficiency of power transfer?
A
98% (12.25 watts / 12.5 watts X 100)
24
Q
There is a relationship between total current and current through the individual components in a circuit. What is this relationship in a series circuit and a parallel circuit?
A
Total current in a series circuit flows through every circuit component but in a parallel circuit total current divides among the available paths.
25
In applying Kirchhoff’s current law, what does the polarity of the current indicate?
Whether the current is entering the junction (+) or leaving the junction (-).
26
Four equal resistors are connected in parallel; each resistor has an ohmic value of 100 ohms, what is the equivalent resistance?
25 ohms (Req = R/N )
27
Three resistors connected in parallel have values of 12 kΩ, 20 kΩ, and 30 kΩ. What is the equivalent resistance?
6 kΩ (Req = 1 divided by 1/R1 + 1/R2 + 1/R3 ) (use power of tens)
28
Two resistors connected in parallel have values of 10 kΩ and 30 kΩ. What is the equivalent resistance?
7.5 kΩ (Req = R1 X R2 / R1 + R2 )
29
What term identifies a single resistor that represents total resistance of a complex circuit?
Equivalent resistor or Req.
30
The total power in both series and parallel circuits is computed with the formula: PT = P1 + P2 + P3 +...Pn. Why can this formula be used for both series and parallel circuits?
In both cases all the power used in the circuit must come from the source.
31
A circuit consists of three resistors connected in parallel across a voltage source. Rl = 40Ω, R2 = 30Ω, R3 = 40Ω, and PR3 = 360 watts. Solve for RT, ES and IR2. (Hint: Draw and label the circuit first.)
RT = 12Ω ( 1RT= 1/R1+1/R2+1/R3)
ES = 120V (ES = ER3 = the root of Pr3 x r3
IR2 = 4A (IR2 = ES/ R2)
32
What is the effect on total resistance and total current in a circuit if an open occurs in (a) a parallel branch, and (b) in a series portion?
(a) Total resistance increases, total current decreases (b) Total resistance becomes infinite, total current is equal to zero
33
What is the effect on total resistance and total current in a circuit if a short occurs in (a) a parallel branch, and (b) in a series portion?
(a) Total resistance decreases, total current increases (b) Total resistance decreases, total current increases
34
If one branch of a parallel network is shorted, what portion of circuit current flows through the remaining branches?
None.
35
What information must be known to determine the component values for a voltage divider?
The source voltage and load requirements (voltage and current).
36
If a voltage divider is required for a load that will use 450 mA of current, what should be the value of bleeder current?
45 mA rule-of-thumb.
37
If the load in question below requires a voltage of +90 V, what should be the value of the bleeder resistor?
If a voltage divider is required for a load that will use 450 mA of current, what should be the value of bleeder current? (45 mA)
2 kΩ.
38
If the source voltage for the voltage divider in question below supplies 150 volts, what is the total current through the voltage divider?
If a voltage divider is required for a load that will use 450 mA of current, what should be the value of bleeder current? (45 mA)
495 mA.
39
In figure 3-67, why is the value of R1 calculated first?
R1 is the bleeder resistor. Bleeder current must be known before any of the remaining divider resistor ohmic values can be computed.
40
figure 3-67, how is (a) the current through R2 and (b) the voltage drop across R2 computed?
(a) By adding the bleeder current (IR1) and the current through load 1(b) By subtracting the voltage of load 1 from the voltage of load 2.
41
In figure 3-67, what is the purpose of the series-parallel network R3, R 4, and R5?
The series-parallel network drops the remaining source voltage and is used to take the place of a single resistor (75 ohms) when the required ohmic value is not available in a single resistor.
42
If the load requirement consists of both positive and negative voltages, what technique is used in the voltage divider to supply the loads from a single voltage source?
The ground (reference point) is placed in the proper point in the voltage divider so that positive and negative voltages are supplied.
43
Is it considered safe for a person to touch any energized low-voltage conductor with the bare hand?
NEVER! All energized electric circuits should be considered potentially dangerous.
44
What should you do if you become aware of a possible malfunction in a piece of electrical equipment?
You should immediately report this condition to a qualified technician.
45
Who should perform CPR?
Only trained, qualified personnel.
46
If circuit voltage is held constant, circuit current will react in what manner as the resistance (a) increases, and (b) decreases?
(a) Decrease (b) increase
47
If circuit resistance is held constant, circuit current will react in what manner as the voltage (a) increases, and (b) decreases?
(a) Increase (b) decrease
48
Which of the following terms applies to the rate at which an electrical force causes motion?
Power
49
What is the current in a circuit with 15 ohms of resistance that uses 135 watts of power?
3 A
50
What is the total power used by a 15-ohm resistor with 4 amps of current?
240 W
51
How much total energy is converted by a l-horsepower motor in 10 hours?
7.46 kWh
52
When Kirchhoff’s voltage law is used to assign polarities to the voltage drop across a resistor, which of the following references is used to indicate the end of the resistor that the current enters?
Negative
53
Which of the following terms applies to a circuit in which there is NO complete path for current?
Open
54
A circuit in which the resistance is almost zero ohms is referred to by which of the following terms?
Short
55
Maximum power is transferred from a source to a load when the value of the load resistance is of what value when compared to the source resistance?
Equal
56
When maximum power is transferred from a source to a load, what is the efficiency of power transfer?
50%
57
A circuit consists of three resistors connected in parallel. R1 = 30 ohms, R2 = 15 ohms, and R3 = 10 ohms. If the current through R2 = 4 amperes, what is the total source voltage?
60 V
58
What is the relationship of total current to the current through a component in (a)
a series circuit, and (b) a parallel circuit?
(a) Equals (b) divides
59
If a current has a negative polarity when Kirchhoff’s current law is applied, which of the following, statements is true of the current?
It is leaving a junction
60
Three equal resistors are connected in parallel and each resistor has an ohmic value of 300 ohms. What is the equivalent resistance of the circuit?
100Ω
61
Three resistors with ohmic values of 120 ohms, 60 ohms, and 40 ohms are connected in parallel. What is the equivalent resistance of the circuit?
20Ω
62
Two resistors with ohmic values of 90 ohms and 45 ohms are connected in parallel. What is the equivalent resistance of the circuit?
30Ω
63
Which of the following terms describes a single resistor that represents a complex circuit?
Equivalent resistor
64
If an open occurs in a series portion of a circuit, what is the effect on (a) total resistance, and (b) total current?
(a) Becomes infinite
| (b) Decreases to zero
65
If an open occurs in a parallel branch of a circuit, what is the effect on
(a) total resistance, and (b) total current?
(a) Increases
| (b) decreases
66
If a short circuit occurs in a series portion of a circuit, what is the effect on
(a) total resistance, and (b) total current?
(a) Decreases
| (b) increases
67
If a short circuit occurs in a parallel branch of a circuit, what is the effect in
(a) total resistance, and (b) total current?
(a) Decreases
| (b) increases
68
If one branch of a parallel network shorts, what portion of the circuit current, if any, will flow through the remaining branches?
All
69
Which of the following circuit quantities need NOT be known before designing a voltage divider?
1. The current of the source
2. The voltage of the source
3. The current requirement of the load
4. The voltage requirement of the load
70
A single voltage divider provides both negative and positive voltages from a single source voltage through the use of a
ground between two of the dividing resistors
71
If you discover a possible malfunction in an electric circuit, which of the following actions should be taken?
Report the malfunction to a qualified technician
72
If a person has stopped breathing and there is NO detectable heartbeat, who should perform CPR?
Trained, qualified personnel only
73
The basic unit of electrical current.
AMPERE
74
The force that tends to make two objects approach each other. Attraction exists between two unlike magnetic poles (North and South) or between two unlike static charges (plus and minus).
ATTRACTION
75
The current through a bleeder resistor. In a voltage divider, bleeder current is usually determined by the 10 percent rule of thumb.
BLEEDER CURRENT
76
A resistor which is used to draw a fixed current.
BLEEDER RESISTOR
77
An individual current path in a parallel circuit.
BRANCH
78
A series-parallel circuit.
COMBINATION CIRCUIT
79
The ability of a material to conduct or carry an electric current. It is the reciprocal of the resistance of the material, and is expressed in mhos or siemans.
CONDUCTANCE
80
Ease with which a substance transmits electricity.
CONDUCTIVITY
81
1) A material with a large number of free electrons. (2) A material which easily permits electric current to flow.
CONDUCTOR
82
A measure of the quantity of electricity.
COULOMB
83
Also called the law of electric charges or the law of electrostatic attraction.
COULOMB’S LAW—states that charged bodies attract or repel each other with a force that is directly proportional to the product of their individual charges and inversely proportional to the square of the distance between them.
84
CPR
Cardio-Pulmonary Resuscitation.
85
The area of a "slice" of an object. When applied to electrical conductors, it is usually expressed in circular mils.
CROSS-SECTIONAL AREA
86
The flow of electrons past a reference point. The passage of electrons through a conductor. Measured in amperes.
CURRENT
87
A short circuit having minimum resistance.
DEAD SHORT
88
The space between and around charged bodies in which their influence is felt. Also called Electric Field of Force or an Electrostatic Field.
DIELECTRIC FIELD
89
An electric current that flows in one direction only.
DIRECT CURRENT
90
A theory of magnetism based upon the electron-spin principle. Spinning electrons have a magnetic field. If more electrons spin in one direction than another, the atom is magnetized.
DOMAIN THEORY
91
The ratio of output power to input power, generally expressed as a percentage.
EFFICIENCY
92
The flow of electrons.
ELECTRIC CURRENT
93
Symbol Q, q. Electric energy stored on or in an object. The negative charge is caused by an excess of electrons; the positive charge is caused by a deficiency of electrons.
ELECTRICAL CHARGE
94
An electrically excited magnet capable of exerting mechanical force, or of performing mechanical work.
ELECTROMAGNET
95
The term describing the relationship between electricity and magnetism. Having both magnetic and electric properties.
ELECTROMAGNETIC
96
The production of a voltage in a coil due to a change in the number of magnetic lines of force (flux linkages) passing through the coil.
ELECTROMAGNETIC INDUCTION
97
Pertaining to electricity at rest, such as charges on an object (static electricity).
ELECTROSTATIC
98
A substance, in chemistry, that cannot be divided into simpler substances by any means ordinarily available.
ELEMENT
99
The force which causes electricity to flow between two points with different electrical charges or when there is a difference of potential between the two points. The unit of measurement in volts
EMF—(Electromotive Force)
100
The ability or capacity to do work.
ENERGY
101
A resistance that represents the total ohmic values of a circuit component or group of circuit components. Usually drawn as a single resistor when simplifying complex circuits.
EQUIVALENT RESISTANCE—(Req)
102
A highly magnetic material, such as iron, cobalt, nickel, or alloys, make up these materials.
FERROMAGNETIC MATERIAL
103
A term used to describe the total force exerted by an action-at-a-distance phenomenon such as gravity upon matter, electric charges acting upon electric charges, magnetic forces acting upon other magnets or magnetic materials.
FIELD OF FORCE
104
A resistor having a definite resistance value that cannot be adjusted.
FIXED RESISTOR
105
In electrical or electromagnetic devices, a general term used to designate collectively all the electric or magnetic lines of force in a region.
FLUX
106
The number of magnetic lines of force passing through a given area.
FLUX DENSITY
107
Zero potential with respect to the ground or earth.
GROUND POTENTIAL
108
The English unit of power, equal to work done at the rate of 550 foot-pounds per second. Equal to 746 watts of electrical power.
HORSEPOWER
109
An electrostatic charge produced on an object by the electric field that surrounds a nearby object.
INDUCED CHARGE
110
Current due to the relative motion between a conductor and a magnetic field
INDUCED CURRENT
111
The electromotive force induced in a conductor due to the relative motion between a conductor and a magnetic field.
INDUCED ELECTROMOTIVE FORCE
| "induced voltage"
112
The act or process of producing voltage by the relative motion of a magnetic field across a conductor.
INDUCTION
113
An electrically charged atom or group of atoms.
ION—Negative ions have an excess of electrons; positive ions have a deficiency of electrons.
114
(1) The algebraic sum of the currents flowing toward any point and the current flowing from that point in an electric network is zero. (2) The algebraic sum of the products of the current and resistance in each of the conductors in any closed path in a network is equal to the algebraic sum of the electromotive forces in the path.
KIRCHHOFF,S LAWS
115
The space in which a magnetic force exists.
MAGNETIC FIELD
116
MHO
Unit of conductance: the reciprocal of the ohm. Replaced by siemens.
117
A prefix meaning one million
MEGA
118
A prefix meaning one-millionth.
MICRO
119
A prefix meaning one-thousandth.
MILLI
120
The unit of electrical resistance. It is that value of electrical resistance through which a constant potential difference of 1 volt across the resistance will maintain a current flow of 1 ampere through the resistance.
OHM
121
The current in an electric circuit is directly proportional to the electromotive force in the circuit. The most common form of the law is E = IR, where E is the electromotive force or voltage across the circuit, I is the current flowing in the circuit, and R is the resistance of the circuit.
OHM'S LAW
122
Two or more electrical devices connected to the same pair of terminals so separate currents flow through each; electrons have more than one path to travel from the negative to the positive terminal.
PARALLEL CIRCUIT
123
The measure of the ability of a material to act as a path for magnetic lines of force.
PERMEABILITY
124
A prefix adopted by the National Bureau of Standards meaning 10-12.
PICO
125
The effect of producing a voltage by placing a stress, either by compression, expansion, or twisting, on a crystal and, conversely, producing a stress in a crystal by applying a voltage to it.
PIEZOELECTRIC EFFECT
126
The condition in an electrical circuit by which the direction of the flow of current can be determined. Usually applied to batteries and other direct voltage sources. (2) Two opposite charges, one positive and one negative. (3) A quality of having two opposite magnetic poles, one north and the other south.
POLARITY
127
The effect of hydrogen surrounding the anode of a cell which increases the internal resistance of the cell.
POLARIZATION
128
Energy due to the position of one body with respect to another body or to the relative parts of the same body.
POTENTIAL ENERGY
129
A 3-terminal resistor with one or more sliding contacts, which functions as an adjustable voltage divider.
POTENTIOMETER
130
The rate of doing work or the rate of expending energy.
POWER—The unit of electrical power is the watt
131
A measure of the opposition that a material offers to magnetic lines of force.
RELUCTANCE
132
The mechanical force tending to separate bodies having like electrical charges or like magnetic polarity.
REPULSION
133
Magnetism remaining in a substance after removal of the magnetizing force.
RESIDUAL MAGNETISM
134
(1) The property of a conductor which determines the amount of current that will flow as the result of the application of a given electromotive force. All conductors possess some resistance, but when a device is made especially for the purpose of limiting current flow, it is called a resistor. A resistance of 1 ohm will allow a current of 1 ampere to flow through it when a potential of 1 volt is applied. (2) The opposition which a device or material offers to the flow of current. The effect of resistance is to raise the temperature of the material or device carrying the current. (3) A circuit element designed to offer a predetermined resistance to current flow.
RESISTANCE
135
The electrical component which offers resistance to the flow of current. It may be a coil of fine wire or a composition rod.
RESISTOR
136
The ability of a material to retain its magnetism.
RETENTIVITY
137
(1) A resistor whose value can be varied. (2) A variable resistor which is used for the purpose of adjusting the current in a circuit.
RHEOSTAT
138
An arrangement where electrical devices are connected so that the total current must flow through all the devices; electrons have one path to travel from the negative terminal to the positive terminal.
SERIES CIRCUIT
139
A low resistance connection between two points of different potential in a circuit, usually accidental and usually resulting in excessive current flow that may cause damage.
SHORT CIRCUIT
140
The new and preferred term for mho.
SIEMANS
141
Stationary electricity that is in the form of a charge. The accumulated electric charge on an object.
STATIC ELECTRICITY
142
A wire-wound, fixed resistor having one or more additional terminals along its length, generally for voltage-divider applications.
TAPPED RESISTOR
143
A junction of two dissimilar metals that produces a voltage when heated.
THERMOCOUPLE
144
1) The maximum error or variation from the standard permissible in a measuring instrument. (2) A maximum electrical or mechanical variation from specifications which can be tolerated without impairing the operation of a device.
TOLERANCE
145
.The measure of the extent to which an atom is able to combine directly with other atoms. It is believed to depend on the number and arrangement of the electrons in the outermost shell of the atom.
VALENCE
146
A wire-wound or composition resistor, the value of which may be changed.
VARIABLE RESISTOR
147
The term used to signify electrical pressure
VOLTAGE—Voltage is a force which causes current to flow through an electrical conductor. (2) The voltage of a circuit is the greatest effective difference of potential between any two conductors of the circuit
148
The difference in voltage between two points. It is the result of the loss of electrical pressure as a current flows through a resistance.
VOLTAGE DROP
149
The practical unit of electrical power. It is the amount of power used when one ampere of dc flows through a resistance of one ohm.
WATT
150
A rating expressing the maximum power that a device can safely handle
WATTAGE RATING
151
A theory of magnetism which assumes that all magnetic material is composed of many tiny magnets. A piece of magnetic material that is magnetized has all of the tiny magnets aligned so that the north pole of each magnet points in one direction.
WEBER'S THEORY
152
The product of force and motion.
WORK
