Electronics Theory Flashcards
Electronics
1
Q
What is an example of a DC source that supplies a constant value of voltage and current for a fixed load?
A
A battery.
2
Q
Define “average DC” for constant output vs pulsating
A
Average value of istantaneous values recorded at even intervals over a period of time
3
Q
One cycle of an AC source is represented as _____.
A
360 Degrees.
4
Q
The frequency of a sine wave is the number of cycles that occur in one second, true or false.
A
True
5
Q
How do you get the rms (effective) value of voltage?
A
V(eff) = V(max) x 0.707 or V(max) / √2
6
Q
How must a voltmeter be used to measure voltage?
A
In parallel
7
Q
How must an ammeter be used to measure current?
A
In series
8
Q
What could happen if the oscilloscope does not have the same reference point?
A
It may short circuit.
9
Q
What is the formula for frequency?
A
f = 1/T
T = time in seconds
10
Q
What is a way to eliminate a fault current condition with the oscilloscope without isolating from ground?
A
Flip the reference lead to the other side of the impedance (load)
11
Q
Semi-conductors have _____ valence electrons.
A
4
12
Q
Electronics made from semiconductor material are known as _____.
A
Solid state devices
13
Q
P-type semiconductors are considered to be _____ charged.
A
Positively
14
Q
N-type semiconductors are considered to be _____ charged.
A
Negatively
15
Q
A boran atom (trivalent atom) creates an _____ of a bond. The hole is the _____.
A
Absence.
Charge carrier.
16
Q
An antimony atom (pentavalent atom) has an _____ electron.
A
Excess
17
Q
Can you use an electronic switch as an isolating switch?
A
No
18
Q
At a PN junction, there is no _____ until there is an applied voltage.
A
Net charge
19
Q
Anode is the lead connected to the _____..
A
P type material
20
Q
Cathode is the lead connected to the _____.
A
N type material.
21
Q
A diode allows current flow in one direction, and _____flow in the opposite.
A
Prevents
22
Q
In order to conduct, a diode requires a minimum Voltage of _____.
A
0.7 V for silicon, 0.3 for germanium.
23
Q
Low current diodes typically are of ____ A or less and normally mounted by _____ or _____.
A
3 A
Soldering to a circuit board
Connected to exposed terminals
24
Q
Medium current diodes are usually up to _____ A and _______ mounted.
A
600 A
Stud mounted, or sometimes press fit.
25
Press fit diodes are often used in _____ applications.
Rectifier
26
Repetitive reverse maximum voltage is the _____.
Instantaneous reverse bias voltage that a diode can safely withstand
27
High current diodes are mounted by ______ that also function as _____.
Squeezing them between two conducting metal plates.
Heat sinks.
28
When checking a diode with a multimeter, a typical reading would be _____.
0.5 mA
29
To check a diode with a multimeter, where do you place the positive and negative leads?
Positive to anode, negative to cathode.
30
Arrows pointing towards a device with a light-dependant resistor, means the device is activated by _____.
Light.
31
Diodes are used in the _____ of fire alarm systems.
Signalling devices
32
Current flow when no light is applied to a diode is called _____.
Dark current.
33
How do you calculate instantaneous voltage from peak/max value?
Multiply peak value by sine of the angle of the instantaneous voltage to be calculated.
34
How do you calculate peak value from effective?
Divide effective by 0.707 or multiply √2
35
Voltage and current peak-to-peak value are symbolized how?
V(pp) and I(pp)
36
Peak to peak values in a sine wave are always _____.
Twice the peak value.
37
Can voltmeters and ammeters measure a moment in time?
No
38
The oscilloscope is a graph of _____ over _____.
Voltage, time.
39
Oscilloscope transducers converts an input value (measured quantity) into a _____.
Voltage signal
40
Heat sinks are most effective when mounted _____ to make use of the _____ effect, which means _____.
Vertically
Chimney
Air moves by convection over the fins
41
Covalent bonding means _____.
Each atom shares its valence electrons with adjoining atoms, making it as though each atom had 8 valence electrons.
42
The Fluke 125B Scopemeter (is, is not) a more versatile troubleshooting and commissioning tool than a bench style oscilloscope.
Is
43
The reference lead on a Fluke 125B Scopemeter (is, is not) grounded.
Is not
44
Using the Fluke 125B, what do you use to test ohms, continuity, diodes and capacitors?
Channel A
45
In a series circuit, if one three resistors were removed, what would happen to the overall current?
Would increase.
46
What is the approximate resistance in our emmenrerds.
0 amps
47
To verify DC Voltage value,, _____.
Multiply # of division x volts per division setting
48
When changing the v/div setting on an oscilloscope, what is being done?
Only changes the scale of the measured malues.
49
Peak voltage = _____.
of divisions x volts per division
50
A period is equal to _____.
of divisions x time per division setting
51
Which type of rectifier has a neutral?
3 phase 1/2 wave
52
How is current applied to the load in a half-wave rectifier?
Every second AC alternation
53
What is the simplest type of rectifier?
Single phase half wave
54
In a single phase half wave rectifier, a single diode is connected in (series, parallel) with the load
Series
55
The DC output of a single phase half wave rectifier is _____ the peak voltage.
31.8%
56
Forrmulas for DC voltage in a single phase half wave rectifier.
V (dc) = V peak x 0.318
Or
V (dc) = 1/π
57
In a single phase half wave rectifier, the peak load voltage is _____ the peak supply voltage.
The same as
58
The ripple frequency of a single phase half wave rectifier is _____.
The same as the supply
59
The diode current in a single phase half wave rectifier is _____.
Same as the load current
60
Full wave rectification is when _____.
The load sees a voltage during both alternations
61
What is the conversion factor for a single phase full wave rectifier?
0.637 of the peak value voltage
62
What is the average DC voltage output of a single phase full wave rectifier?
63.7% of peak instantaneous voltage
63
What are the formulas for the value of voltage output for a single phase full wave rectifier?
V(DC) = V(peak) x 0.637
V(DC) = V(peak) x 2/π
64
The half-wave rectifier splits an AC waveform into _____ that add together to equal the input voltage.
Postive and negative half cycles
65
The average value of a 120 V(ac) sine wave is _____.
0 V
66
What is the rating of a diode represents reverse bias limit?
V(rrm)
67
What does a suppression diode do?
Control the cemf spike when an inductive DC circuit is opened.
68
If a silicon diode is connected in series to a load, and a voltage is applied to the circuit, what would the voltage reading at the diode be if the diode is forward bias?
0.7 V
69
Conductors have how many valence electrons?
1-3
70
Insulators have how many valence electrons?
5-8
71
What percentage of the peak voltage in a three-phase half wave rectifier is the output voltage?
82.7%
72
What percentage of the peak voltage in a three-phase full wave rectifier is the output voltage?
95.5%
73
In which rectifier must a 4-wire wye connection be used?
Three phase half wave
74
Is a neutral required in a three phase half wave rectifier?
Yes
75
What is the ripple frequency in a three-phase half wave rectifier?
3x the supply
76
What is the ripple frequency in a three-phase full wave rectifier?
6x the supply
77
In a three-phase half wave rectifier, the peak load voltage is equal to the ______ voltage.
Peak phase (line to neutral)
78
In a three-phase half wave rectifier, when one diode is conducting the other two must ______.
Block the line to line voltage
79
What is the load current of each diode in a three phase half wave rectifier?
1/3 of the load current
80
The assembly of a three phase full wave rectifier has how many leads? What are they?
Five.
3 AC input leads
2 DC output leads
81
Three sets of modular assemblies containing two diodes each could be used as a ________ rectifier, and would be mounted to a _____ for heat dissipation.
Three phase full wave.
Heat sink
82
In a three phase full wave rectifier, the peak load voltage is equal to ______.
Peak line voltage
83
How do battery chargers restore the electrical charge to storage batteries?
Rectifying AC voltage to provide DC voltage
84
Battery chargers are rated in what capacity?
Current
85
What is "trickle charge"?
Charging at a slow rate, ie a 6 or 12 V battery @ 2 A
86
A fast charge would be __ V at __ A
12 V at 10 A
87
What are the two main components of a battery charger?
A transformer with adjustable tap settings
A rectifier
88
The secondary of a transformer in a battery charger is connected in _____ with ______ windings.
Parallel
Two center-tapped
89
Connecting the transformer secondary of a battery charger in parallel achieves what?
Increased current capacity with lower cost (smaller conductors)
90
Four of the eight ends of the transformer secondary windings are connected solidly to the ______ rail of the rectifier.
Negative rail
91
Four ends of the transformer secondary windings are connected to the _____ of four _____.
Anodes
Press-fit diodes
92
What might happen if two diodes in parallel aren't closely matched?
One diode might carry more of the load and cause it to overheat
93
The diodes in the rectifier of a battery charger are press-fit into a _____ that forms part of the ______ rail.
Heat sink
Positive
94
In a center-tapped rectifier of a battery charger, each leg carries ____ of the load current, _____ of the time.
1/2
1/2
95
If two sets of two 25 A parallel-connected diodes are used in the rectifier of a charger, what is the load current capacity?
100A
96
Overcurrent circuit breakers on a battery charger are connected in _____.
Parallel
97
When does the current transfer in a battery charger take place?
When the charger voltage is higher than the battery voltage.
98
Why is the current greater when a battery has a lower voltage? When it is nearing full charge the current is less... what is this process called?
The difference between peak charger voltage and battery voltage is higher.
Tapered charging
99
If the peak output voltage of a battery charger is normal but the DC avg is half the expected value, what is most likely the issue? What does this do to the waveform
One pair of diodes has failed.
It appears like that of a half wave rectifier
100
Corrosion is an ______-______ process.
Electro-chemical
101
What occurs by an 'anodic' reaction?
Change from a metallic form to combined form (ie iron oxide
102
What does an anodic reaction produce?
Free electrons
103
Does corrosion occur at the cathode?
No
104
Where does corrosion occur?
At the anode
105
What is cathodic protection?
Connection of an external anode to the metal being protected - passes a DC current to make all protected metals cathodic, so they do not corrode.
106
What are the four parts of the corrosion process?
Anode, cathode, electrolyte, metallic path.
107
When does corrosion occur?
When all four parts are present.
108
Where does current flow by chemical means in relation to the anode in a corrosion cell?
From the surface of the Anode metal to the electrolyte
109
An oxidation reaction occurs when _____.
Current is carried by the metal moving into solution as positively charged ions
110
Where does current flow by chemical means in relation to the cathode in a corrosion cell?
From the electrolyte to the metal
111
What is a reduction reaction?
The cathode gaining electrons from the electrolyte
112
Where do ions flow?
In the electrolyte
113
What is the electrolyte?
Any material in contact with both the anode and cathode that allows oxidation and reduction reactions.
114
What is the metallic path?
Any metal that completes a path between the anode and cathode, allowing electrons to flow
115
Electron flow must be present for _____-_____ corrosion to occur
Electro-chemical
116
Can a pipeline be used as the metallic path in a cathodic protection system for the pipeline itself?
Yes
117
What are the two most common types of cathodic protection systems?
Sacrificial (galvanic) anode
Impressed current system
118
What are three common materials used for the sacrificial anode type of system?
Aluminum
Zinc
Magnesium
119
What are some applications of a cathodic protection system?
Storage tank
Potable water distribution
Sewage lifts
Steel pipe
Pier support
Concrete reinforcing steel
120
Cathodic protection rectifiers are powered by __ equipment that provide __ for what type of protection systems?
AC current
DC current
Impressed current systems
121
The seven parts of a rectifier used for cathodic protection system are:
1: Adjustable step down transformer
2: Rectifier stacks
3: Shunt to measure output current
4: Meters to indicate output current and voltage
5: Circuit breakers
6. Lightning arresters
7: Transformer tap connections
122
What are the two general types of rectifier stacks?
Selenium plates
Silicon diodes
123
Which type of rectifier stack should be used for high current & high voltage?
Silicon diode
124
A selenium plate unit is more efficient than a silicon diode unit. T or F
False
125
Surge protection is provided to silicon diode units via _____ _____ _____.
Metal Oxide Varistors
126
On manually controlled rectifier units, the center tap is the _____ connection and the negative/positive lugs are the _____ from the stacks.
Input
Output
127
Automatic rectifiers are sometimes used when _____ and _____ is changing.
Structure size
Cathodic protection circuit resistance
128
How can an automatic rectifier be controlled?
Potential control, current control, voltage control
129
Can a current or voltage controlled rectifier be used in an elevated water tank?
No
130
Current controlled rectifiers would be used in what type of situation?
Changing cathodic protection circuit resistance
131
Meters and/or a shunt would be located between the _____ and the ______.
Stacks
Output lug
132
What part(s) of a cathodic protection system are considered the 'input' section?
Supply circuit, incoming circuit breaker
133
What part(s) of a cathodic protection system are considered the 'output' section?
Rectifier circuit, anodes, instrumentation and reference leads
134
What section of the CEC covers cathodic protection systems?
Section 80
135
What materials are normally used as an anode in an impressed current system?
Graphite, high silicon cast iron, platinum or mixed metal oxide
136
What is usually used as the earth contact backfill to provide a uniform electrolyte?
Coke breeze or calcined fluid petroleum coke
137
What must be done to prevent the copper lead wire from becoming part of the anode system?
Special insulation
