IE 222 Flashcards
1
Q
why is resistance inserted into a cct
A
-reduce current
-produce voltdrop
2
Q
2 main types of resistors used in electronic ccts
A
- carbon composition
- wire wound
3
Q
desribe carbon composition resistrors
A
-finley divided carbon powdered with insulating material to get the right resistance
-enclosed in a plastic case for insulation and mechanical strength
4
Q
what are axis leads on carbon resistors
A
-metal caps on the ends of the resistors used for soldering to a cct
5
Q
carbon resistors are avalible in resistance values of _______ to __________ohms
A
0.1 to 20 megaohms
6
Q
value and tolerance of resistors are found from what
A
colour coded bands on the resistor
7
Q
A resistor should have a wattage rating high enough to dissipate the Ir squared power produced by the _____________ flowing through the resisor without becoming too hot
A
current
8
Q
The power rating is a physical property depending on what 2 things
A
-resistor construction
-physical size
9
Q
carbon resistors are used in low power applications and are avalible in what sizes
A
- 1/8W
-1/4W
-1/2W
-1W
2W
10
Q
the bigger the wattage of a resistor the ____________- the physical size
A
bigger
11
Q
how to find power (w) when tou know the current and resistance
A
I squared R
12
Q
How to find the current in a resistor when you know the power and the resistance
A
P divided by R square rooted
13
Q
What is the construction of wire wound resistors
A
-resistance wire wrapped around an insulating core
14
Q
What insulating materials are commonly used in wire wound resistors
A
-procelin
-cement
-bakelite
-plain pressed paper
15
Q
the wire is bare in a wire wound resistor but usually the entired unit is ___________ in an insulator
A
encased
16
Q
In a wire wound resistor the length of the wire used and its specific resistance determine the ____________ of the unit
A
resistance
17
Q
where to find the resistance value, tolerance and power rating on a wire wound resistor
A
-stamped on the case of wire wound resistors
18
Q
The tolerance of most wire wound resistors is ________
A
+- 5%
19
Q
wire wound precision resistors have a tolerance of _________. And where are they used
A
+-1%
-used where accurate stable resistance values are required such as meter shunts and multipliers
20
Q
________________ resistors are avalible in power ratings from 1 watt to 2 watts
A
carbon composition
21
Q
Resistors are used in 3 different applications:
A
- heat
2.cause voltage drop
3.limit current
22
Q
A heating resistor creates _____ when a voltage is applied to it
A
heat
23
Q
Where are heating resistors used
A
-appliance heating elements
-filiaments
-incadescent lamps
-electric heating.
usef to warm up a certain part of the cct
24
Q
Heating resistors are usually __________
A
wire wound
25
Heating resistors are rated in ___________ and ___________
watts
volts
26
A resistor places in ________- with other cct components would have a volt drop theorfore reducing the voltage to the rest of the cct
Series
27
Current limiting resistors are placed in _________ with and ahead of other cct compenents in electrical ccts
series
28
The _________ in the cct even with all other components short circuted, is limited by the resistance of the current limiting resistor
maximum current
29
the colour code of a resistor is a system to indicate the _____________
resisitance value of fixed resistors
30
On a resistor what does the
A) first colour band coloses to the edge indicate
B)The second colour band
C)The third colour band
D) the forth colour band
a)first digit in the numerical value of resistance
b)Second digit
c)The decimal multiplier giving the number of zeros after the 2 digits
d) Gives the tolerance
31
What is the acurname for the resistor band colours and their values
Bad (black) 0, x1 (no zeros)
Beer( Brown)!, x10, (1zero)
Rots(Red), 2, x100, (2 zeros)
Our (orange),3, x 1000, (3 zeros)
Young (yellow), 4, x 10000 (4 zeros)
Guts(green), 5, x 100000 (5 zeros)
But (blue), 6, x 1000000 (6 zeros)
Vodka (violet), 7, x 10000000 (7 zeros)
Goes (grey) 8,x 100000000 (8 zeros)
Well (white), 9, x1000000000 (9 zeros)
Get (gold), multiplier is x 0.1, tolerance is +-5%
Some (silver), multiplier is x0.01, tolerance is +-10%
Now (no colour), tolerance +- 20%
32
Variable resistors can be __________ or _______ type and are called __________.
-wire wound\
-carbom
-controls
33
carbon controls are commonly avalible in resistance values from ____ohms to _______ohms. and their power ratings are usually__________
-100 ohms to 5 Mega Ohms
-1/2 watts to 2 watts
34
wire wound controls are avalible in __ ohm to _________ohms
1 ohm to 100K ohms
35
A rheostat is a variable resistance connected in ___________ with the load to vary the current
series
36
A moving-coil meter movement responds to _____________
current
37
A moving coil meter movement is used for measuring ___________ by the addition of a high resistance in series with the movement
voltage
38
A movings-coil meter movement will have full scale deflection current ratings of _______ to _________
50 micro amps to 250 microamps
39
A moving coil meter has ________ internal resistance
low
40
Voltage range can be___________a lot by adding a series resistor (multiplier resistor) to the meter cct.
increased
41
What is the value of the Imeter or I full scale deflection current and what are the typical values?
-amount needed to deflect the pointer all the way to the right to the last mark on the printed scale.
-typical values: 100 micro amps to 30 milliamps
42
What is the value of Rmeter?
-internal resistance of the wire of the moving coil
43
What is the purpose of a multiplier resistor or series resistor and how are they hooked up in the cct? what happens to the resistance when the voltage is increased?
-added in series with the meter movement
-limits curent flow in the meter so it wont exceed the meter full scale deflection rating.
-Resistance has to be increased for each increase in the voltage range
44
What is internal resistance or total resistance? What happens when voltage range is increased?
-the sum of the meter coil resistance plis the resistance of the multipliers or resistors
-as voltage range of the voltmetrer is increased the internal resistance of the meter must also must be increased to limit current to meter coil. The full scale deflection current must never be exceeded
45
How is the sensitivity measured and what is it
-measured in ohms-per-volt
-amt of resistance required for 1 volt of deflection
-ohms-per-volt value is the same for all ranges
-determined by the FSD current Im of the meter movement
46
on a variable resistor what happens as the shaft control rotates
-variable arm moves wiper to make contact at different points
-When contact moves closer to terminal 1 the resistance decreases between terminal 1 and terminal 2 but increases between terminal 2 and terminal 3
47
The current for full-scale deflection for a typical moving coil meter movement is:
50 to 250 micro amps
48
To convert a moving-coil meter movement to a voltmeter a _____ resistance is connected in ______ with the coil
- high
-series
49
The resistor used in series with the moving coil in a voltmeter is called a ?
multiplier or series resitor
50
What is the formula for finding resistance of a miltiplier ?
Rmult= Full scale voltage divided by Full scale current =___ then subtract by the resistance of the meter
51
For internal resistance as the voltage range of a voltmeter is increased, the internal resistance of the instrument must be ________
increased
52
Formula for finding internal resistance of a volt meter?
Rint= full scale deflection voltage x ohms-per-volt
53
What are the 2 voltmeter ccts that are in common use
-individual multiplier
-series multiplier
54
Do sensitivity ratings change?
no they stay the same
55
Formula to find the sensitivity rating?
= 1 divided by the full scale deflection current
56
What is voltmeter loading
-meter gives a lower indication of the voltage drop than actually existed before the meter was connected
57
Whats the rule of thumb for internal resistance
-If the internal resistance of the voltmeter is 10 or more times the resistance across where the measurement is made, the loading effect is ignored
58
How can considerable improvement in meter preformance can be achived
- vaccum-tube
-transirot amplifier in a multimeter type of instriment
59
What does an amplifier in a meter do
-allows measurement of smaller voltages and presents higher impedance to the cct under test
-reduced loading effect
60
on a osciliscope what happens when you rotate the time/div control
-time changes at bottom centre of the screen
-the longer the time the longer it takes the trace to travel from left to right
61
What does the trigger level of an osciliscope determine
-determine where the scope will trigger
-As arrow goes up, voltage at the bottom of the screen is positive
-below the centre line the voltage is negative
62
on a osciliscope what happens on the AC and DC positions
AC- inserts a capacitor put into the cct to block any DC current
DC- allows AC and DC to be measured
63
on a osciliscope what values are on the X and Y axis
x- time
y-voltage (1v/division)
64
on an osciliscope of the sine wave doesnt start and end at the same points, it can be corrected by what
Adjust the trig level
65
on an osciliscope if the trigger voltage is ser above or below the peak of the wave , the display becomes unstable or goes blank, why does this happen?
-triggering is lost
-set the source or coupling incorrect
66
on a oscilisope, higher volts/division setting ____________ the height of a displayed wave
increases
67
on a osciliscope increasing frequency of the input signal _________ the number of cycle displayed. Why does this happen?
increases
-happens bc more cycles occur in the same time period
-decreasing the frequency gives the opposite result.
68
on a oscilicope what does adjusting the output level of the signal genrator do
-change the voltage applied to the scope
69
how to calculate rms voltage
0.707 x peak value or 0.707 x peak-peak voltage divided by 2
70
peak voltage is ____________- the peak to peak voltage
half
71
What does a scope-meter do
-combines the finctions of a voltmeter and osciliscope
72
What happens when you press the end of a rocker switch on a scope meter
volts/division and time/divsion can be moved up and down
73
What creates the glowing trace on the screen of a CRT oscilliscope
-narrow beam of electrons that strikes the phospher coating on the inside of the tube which makes it glow
74
Why is the trace sometimes only a dot and othertimes a line on a CRT oscilliscope?
dot- when the beam is stopped or moving across the screen very slowly
line- when speed is increased it turns into a line
75
What is th epurpose of the variable volts/ division controls, and where should they be set for all voltage measurements on a CRT oscilliscope
-allow for vertical scaling of display to ve ajusted to values within the normal range settings
-set to the calibrate position for all voltage measurements
76
will a shorter time base increase or decrease the width of each cycle displayed on the screen on a CRT oscilliscope
inctrases
77
Compare the method used to display and alter volts/division and time/ divison settings on a CRT oscilliscope to the method used on a scope-meter
Oscilliscope- Rotarty switches, read from position of pointer
Scope- rocker switches, listed on display
78
______________ are the basic building materials from which all mater is constructed. what are some examples
elements
-gold,ion,carbon,hydrogen
79
How many valence electrons does each have:
a) conductor
B)insulator
c)semi-conductor
a) 1-3
b)5-8
c)4
80
The smallest partical an element can ve reduced to is an _________-
atom
81
an atom can be broken down into what
-electrons
-protons
-neutrons
82
Protons and neutrons make up the centre of the atom and its called the ________
neucleus
83
what is electrostatic force
negative attracted to positive and vise versa
84
What is coulombs law
-like charges repel and unlike charges attract
85
What effects atoms and upsets their balanced state
-heat
-light
-electrostatic field
-chemical and magnetic reactions
86
An atom that is no longer in its neutral state is called a _______
ion
87
If an atom loses one or more electrons its called a ____________ ion and has a ___________charge because it has more _________ than ________
-positive
-positive
-protons
-electrons
88
An atom that gains one or more electrons is called a ________ ion because it has more ____________ than _________
negative
electrons
protons
89
Electrons oribit the neucleus at a _________ speed
high
90
The outer shell of an atom is called a __________
valence shell
91
The valence shell of an atom cant hold more then __________ electrons
8
92
A material that has one to three electrons in its valence shell is called a _______
conductor
93
Why can the electron in the valience shell easily be set free? what are some examples
-bc of the weak attraction of the neucleus. these become free electrons
-copper,silver,gold,aluminum
94
the ____________ valence electrons the better a conductor
less
95
The _________-- valence electrons the better the insulator
more
96
Semi conductors have a valence shell of _________ electrons
4
97
What are 2 pure semiconductor materials
1.silicon
2.germanium
98
Components that are made of semi-conductor materials are often referred to as ______________
-solid state components bc they are made up of solid materials.
99
Advantages of semi conductors
-more rugged
-more reliable
-operate cooler
-more efficient
-operate at low-voltages and use less power
-safer
-smaller in size
-less expensive
100
Disadvantages of semi conductors
-highly susceptable to changes in temperature
-damaged if operated at high temps
-easily damaged if exceed power distrivution limits
101
Sharing electrons creates a ___________
bond
102
What does a crystalline structure of a semi conductor look like
-each atom tends to be stable and will not easily give up or accept electrons
103
when electrons break away from a covalent bond it creates a ________
open space
104
What does doping do to electrons
the conductivity of these materials can be increased
105
The dopant atom used to form an N-type crystal is said to be _________, having _____ valence electrons
prevalient
5
106
In a N-type crystal the _______ are the majority and the ___________ are the minority
Electrons
holes
107
how is a P-type crystal is produced
-adding to the pure semiconductor a dopant material that has 3 valence electrons
108
In a P-type crystal the ________ are the majority carriers and the __________ are the minority carriers
holes
electrons
109
In a P-N junction both p-type and n-type crystals will conduct __________
electricity
110
A P-N junction acts like a __________
resistor abd will conduct current in both directions
111
When P type and N type crystals are placed together as a pair they form a ________
p-n junction
112
what is diffusion
Electrons from the N-type material are attracted across the junction and fill holes in the P-type material at the junction
113
The internal voltage that is set up is called _______ and the area in which it is set up in is the depletion area
potential barrier or barrier voltage
114
The barrier voltage depends on the extent of doping and is about ___________________v for silicon
0.6v
115
how do you overcome the depletion region
0.6V has to be applied to the diode
116
When the positive terminal of a DC power supply is connected to the N-crystal an dnegative terminal is connection to the P-crystal the diode is connected __________ biased and __________ conduct
reverse
wont
117
What happens if P-crystal and N-crystal are connected reversed biased
-causes a widening of the depletion area and no current will flow
118
What will happen if the reverse voltage is increased to a value that exceeds the peak reverse voltage of the diodein a N-crystal and P-crystal
- diode will go into avalance and the reverse current will destroy the diode
119
The P type material of a junction has an excess of __________
holes
120
the majority carriers in P type material are ___________ and the minority carriers are _________________
holes
electrons
121
A forward biased diode has _________ resistance and a reversed biased diode has _____________ resistance
low
high
122
The forward break over voltage for a silicon PN junction is about ___________ volts
0.6
123
In reversed biased the junction tries to block _________ from flowing
current
124
What happens if you exceed peak inverse voltage
-avalange and diode is destroyed
125
In an "ideal" silicon diode what would happen when it is forward biased by 0.6V
go into immediate conduction
126
what would happen in a diode if the forward current doesnt exceed the diodes forward current rating
diode will be able to continue in the forward biased state
127
what will happen when theres leakage in a diode
-current will increase to the point where at near rated peak reverse voltage, the leakage current will become high and diode will be destroyed and damaged an a avalanch will occur
128
Diodes are rated for the _______________- that the diode can safley handle. and what is it called
max reverse biase voltage
Peak inverse voltage or peak reverse voltage
129
What happens if the PRV/PIV rating is exceeded and what is it called
-diode will breakdown
-damaging current will flow
-called avalanch current
130
What are the 2 terminals on a diode called
annode
Cathode
131
what is a rectifier or rectification
changes AC to DC
132
how are diodes used to steer current
only conduct when switches are in a certain position
133
How can a diode be used as a dimmer switch
-switch in high- the light will get full AC input
low- position the light will only see the positive alternations and wont be as bright
134
How can a diode be used as meter protection
-Protect meters from reverse polarity by connectin gthe diode in series with the meter movement
-protects from heavy excessive fault curren tby paralleing diodes across the meter movements
135
the lower the ripple frequency % the ___________
better it is
136
For the % ripple always go by the __________ voltage
output
137
the average value for one half cycle of an AC sine wave is _____________
0.637 Emax
138
The average DC output voltage that a half wave rectifier will deliver to a resistive load is _________ times the ___________ input voltage. what is the formula
0.45 times
-VDC= 0.45 x Vrms
139
The peak instantaneous voltage in an ac voltage is ___________ times the RMS values. what is the equation
1.414
-PRV= 1.414 x Erms
140
IF the half wave cct supplies a capacitive load, the diode must have a PRV rating ___________ than ________ the peak line voltage
greater than twice
141
in a diode the average forward current rating must be ___________ the average current load
equal
Idc=I load
142
What is a centre tapped transformer
Has a secondary that supplies 2 equal output voltages connected in series with a tap off the cenrre connection
143
When DC current is allowed to flow in the load for both hald cycles of the input, the cct is known as a ____________.
full wave rectifier
144
What does a full wave bi-phase rectifer use for diodes and the transformer?
1. the full wave bi-phase rectifier cct uses 2 diodes with a centre tapped transformer
145
What would happen if both diodes were connected in reverse
output polarity would be reversed
146
in a bi-phase or centre tapped transformer There are _______ output pules for each input cycle and th eoutput frequency is ___________ the input frequency
two
doubled
147
The average value of one half cycle of a AC wave form in a Bi phase is _______
0.637 Emax
148
Each diode conducts for only one half cycle and the average current through the diode will be __________ of the average load current
half
149
The bridge rectifier cct does not need a centre tapped transformer but does require _________ diodes
4
150
For a full wave bridge rectifier the output wave form occurs _______ for each input wave form
twice
151
For a full wave rectifier each diode must have a PRV rating ___________ than the peak of the AC supply voltage
equal or greater
152
Each diode on a bridge rectifier for only conducts for one half cycle and the average cuurent through each diode, theirfore the cure nt of the diode will be _________ of the average load curent?
one half
If=0.5x Idc
153
the ripple frequency on a bridge rectifier will be ________ the AC line frequency
twice
Hz of the ripple= 2 x Hz ac
154
what are the 3 applications of capactitors
1. charged capacitor as a power supply
2. Resistor and capicitor together can be a timing cct
3. Capacitors used as filters in rectified DC power supplies to smooth out the pulses of DC and get a higher quality DC supply
155
what is a capacitor
-charge storage device formed by seperating two conductive "plates" with a dielectric (insulating material)
156
In a capacitor current stops when the current has _____________
charged to the full supply voltage
157
A charging time of a capacitor can be reduced by what
-Adding resistance in series with the capacitor
158
A capacitor opposes changes in ______________
voltage
159
What happens when the supply voltage exceeds the capacitor voltage
-Capacitor draws a charging current
160
what happens when the supply voltage and the capacitor voltage is equal
-capacitor voltage balances the pressure of the supply voltage and there is no current
161
What happens in a capacitor when the supply voltage drops below the capacitor voltage
-capacitor discharges back into the cct
162
How are commercials capacitors classified
-according to the dielectric
-ex: mica,paper,ceramic, electrolytic
163
What precaution do you have to use with electrolytic capacitors
-careful with the polarity
164
What is mica
- a rock
-its a stable material
165
what happens when mica is used as the dielectric (insulator) in a capacitor
-stable
-reliable
166
how do mica sheets give the required capacitence to the capacitor
-sheets are stacked between tinfoil sections for the conducting plates to provide the required capacitance
167
advantages of polystyrene plastic film
-high insulation resistance
-low losses
-longer life
168
How are ceramic capacitors made
earth fired under extreme heat. Very high values
169
What capacitors provide the most capacitence in the smallest space with the smallest cost
electrolytic
170
why must electrolytic capacitors must be connected
-applied voltage maintains the positive electrode more positive than the negative terminal
171
What happens if an electrolytic capacitor is connected with the wrong polarity
-reversed electrolysis forms gas and the capacitor becomes hot and may explode
172
Ceramic disc capacitors usually have a tolerance of ______________
+- 20%
173
paper capacitors usually have a tolerance of________________
+-10%
174
Why is the AC voltage lower for a capacitor
-should be operated close to rated voltage to provide the rated capacitence
175
What does an RC cct have
resistor and capacitor in series
176
Why will an RC cct charge a capacitor quicker
lower resistance
177
Why wont electrons flow through a capacitor
dielectric prevents it
178
The charging rate (current) ________ as the capacitor voltages approaches the source voltage
decreases
179
The time required to charge a capacitor is determined by what
-amt of charge to ve moved (capacitence) and the current flow in the cct determined by R
180
How can you determine the charge that any capacitor will take to charge
Q= c x E
181
How to calculate the time constant in a capacitor
T= R x C
182
How many time constants does it take to fully discharge a capacitor
5 times
183
A _____________ frequency Ac, when rectified will provide A better DC than low frequency
high
184
What is it called If the output of A Rectifier is measured with an AC voltmeter the meter will still look at the amount of change and convert that to an AC value
ripple voltage
185
A low percent ripple value is much better than a ____________ percent ripple value
high
186
What is the percent ripple for a pure DC signal
0%
187
what does adding a choke do to the cct
choke adds more filtering and creates less filter
188
What is the max current that a 1k ohm, 1/4W resistor can safley carry?
250 micro amps
189
What effect does voltmeter loading have on a cct
The voltmeter decreases the voltage across the part of the cct it is connected to
190
What is created when pure semi conductor material is doped with trivalent dopant?
P-type material
191
What is created when pure semi conductor material is doped with prevalient dopant?
N-type material
192
What are the majority carriers in N type material
electrons
193
An ohm meter is used to test a diode. The ohmeter indicated the infinate resistance when the common (black) probe is connected to the cathode and the positive (red) probe is connected to the anode. What does this reading indicate?
-the diode has failed in an open state
194
True or false, Capacitors oppose a change in current
False. they oppose a change in voltage
195
A moderatly sized capacitor is connected in parallel to the output of a lightly loaded full wave rectifier. What effect will this have on the cct?
The DC voltage measured on the rectifier output will increase
