IE 222 Flashcards
why is resistance inserted into a cct
-reduce current
-produce voltdrop
2 main types of resistors used in electronic ccts
- carbon composition
- wire wound
desribe carbon composition resistrors
-finley divided carbon powdered with insulating material to get the right resistance
-enclosed in a plastic case for insulation and mechanical strength
what are axis leads on carbon resistors
-metal caps on the ends of the resistors used for soldering to a cct
carbon resistors are avalible in resistance values of _______ to __________ohms
0.1 to 20 megaohms
value and tolerance of resistors are found from what
colour coded bands on the resistor
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
current
The power rating is a physical property depending on what 2 things
-resistor construction
-physical size
carbon resistors are used in low power applications and are avalible in what sizes
- 1/8W
-1/4W
-1/2W
-1W
2W
the bigger the wattage of a resistor the ____________- the physical size
bigger
how to find power (w) when tou know the current and resistance
I squared R
How to find the current in a resistor when you know the power and the resistance
P divided by R square rooted
What is the construction of wire wound resistors
-resistance wire wrapped around an insulating core
What insulating materials are commonly used in wire wound resistors
-procelin
-cement
-bakelite
-plain pressed paper
the wire is bare in a wire wound resistor but usually the entired unit is ___________ in an insulator
encased
In a wire wound resistor the length of the wire used and its specific resistance determine the ____________ of the unit
resistance
where to find the resistance value, tolerance and power rating on a wire wound resistor
-stamped on the case of wire wound resistors
The tolerance of most wire wound resistors is ________
+- 5%
wire wound precision resistors have a tolerance of _________. And where are they used
+-1%
-used where accurate stable resistance values are required such as meter shunts and multipliers
________________ resistors are avalible in power ratings from 1 watt to 2 watts
carbon composition
Resistors are used in 3 different applications:
- heat
2.cause voltage drop
3.limit current
A heating resistor creates _____ when a voltage is applied to it
heat
Where are heating resistors used
-appliance heating elements
-filiaments
-incadescent lamps
-electric heating.
usef to warm up a certain part of the cct
Heating resistors are usually __________
wire wound
Heating resistors are rated in ___________ and ___________
watts
volts
A resistor places in ________- with other cct components would have a volt drop theorfore reducing the voltage to the rest of the cct
Series
Current limiting resistors are placed in _________ with and ahead of other cct compenents in electrical ccts
series
The _________ in the cct even with all other components short circuted, is limited by the resistance of the current limiting resistor
maximum current
the colour code of a resistor is a system to indicate the _____________
resisitance value of fixed resistors
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
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%
Variable resistors can be __________ or _______ type and are called __________.
-wire wound\
-carbom
-controls
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
wire wound controls are avalible in __ ohm to _________ohms
1 ohm to 100K ohms
A rheostat is a variable resistance connected in ___________ with the load to vary the current
series
A moving-coil meter movement responds to _____________
current
A moving coil meter movement is used for measuring ___________ by the addition of a high resistance in series with the movement
voltage
A movings-coil meter movement will have full scale deflection current ratings of _______ to _________
50 micro amps to 250 microamps
A moving coil meter has ________ internal resistance
low
Voltage range can be___________a lot by adding a series resistor (multiplier resistor) to the meter cct.
increased
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
What is the value of Rmeter?
-internal resistance of the wire of the moving coil
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
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
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
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
The current for full-scale deflection for a typical moving coil meter movement is:
50 to 250 micro amps
To convert a moving-coil meter movement to a voltmeter a _____ resistance is connected in ______ with the coil
- high
-series
The resistor used in series with the moving coil in a voltmeter is called a ?
multiplier or series resitor
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
For internal resistance as the voltage range of a voltmeter is increased, the internal resistance of the instrument must be ________
increased
Formula for finding internal resistance of a volt meter?
Rint= full scale deflection voltage x ohms-per-volt
What are the 2 voltmeter ccts that are in common use
-individual multiplier
-series multiplier
Do sensitivity ratings change?
no they stay the same
Formula to find the sensitivity rating?
= 1 divided by the full scale deflection current
What is voltmeter loading
-meter gives a lower indication of the voltage drop than actually existed before the meter was connected
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
How can considerable improvement in meter preformance can be achived
- vaccum-tube
-transirot amplifier in a multimeter type of instriment
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
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
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
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
on a osciliscope what values are on the X and Y axis
x- time
y-voltage (1v/division)
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
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
on a oscilisope, higher volts/division setting ____________ the height of a displayed wave
increases
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.
on a oscilicope what does adjusting the output level of the signal genrator do
-change the voltage applied to the scope
how to calculate rms voltage
0.707 x peak value or 0.707 x peak-peak voltage divided by 2
peak voltage is ____________- the peak to peak voltage
half
What does a scope-meter do
-combines the finctions of a voltmeter and osciliscope
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
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
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
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
will a shorter time base increase or decrease the width of each cycle displayed on the screen on a CRT oscilliscope
inctrases
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
______________ are the basic building materials from which all mater is constructed. what are some examples
elements
-gold,ion,carbon,hydrogen
How many valence electrons does each have:
a) conductor
B)insulator
c)semi-conductor
a) 1-3
b)5-8
c)4
The smallest partical an element can ve reduced to is an _________-
atom
an atom can be broken down into what
-electrons
-protons
-neutrons
Protons and neutrons make up the centre of the atom and its called the ________
neucleus
what is electrostatic force
negative attracted to positive and vise versa
What is coulombs law
-like charges repel and unlike charges attract
What effects atoms and upsets their balanced state
-heat
-light
-electrostatic field
-chemical and magnetic reactions
An atom that is no longer in its neutral state is called a _______
ion
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
An atom that gains one or more electrons is called a ________ ion because it has more ____________ than _________
negative
electrons
protons
Electrons oribit the neucleus at a _________ speed
high
The outer shell of an atom is called a __________
valence shell
The valence shell of an atom cant hold more then __________ electrons
8
A material that has one to three electrons in its valence shell is called a _______
conductor
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
the ____________ valence electrons the better a conductor
less
The _________– valence electrons the better the insulator
more
Semi conductors have a valence shell of _________ electrons
4
What are 2 pure semiconductor materials
1.silicon
2.germanium
Components that are made of semi-conductor materials are often referred to as ______________
-solid state components bc they are made up of solid materials.
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
Disadvantages of semi conductors
-highly susceptable to changes in temperature
-damaged if operated at high temps
-easily damaged if exceed power distrivution limits
Sharing electrons creates a ___________
bond
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
when electrons break away from a covalent bond it creates a ________
open space
What does doping do to electrons
the conductivity of these materials can be increased
The dopant atom used to form an N-type crystal is said to be _________, having _____ valence electrons
prevalient
5
In a N-type crystal the _______ are the majority and the ___________ are the minority
Electrons
holes
how is a P-type crystal is produced
-adding to the pure semiconductor a dopant material that has 3 valence electrons
In a P-type crystal the ________ are the majority carriers and the __________ are the minority carriers
holes
electrons
In a P-N junction both p-type and n-type crystals will conduct __________
electricity
A P-N junction acts like a __________
resistor abd will conduct current in both directions
When P type and N type crystals are placed together as a pair they form a ________
p-n junction
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
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
The barrier voltage depends on the extent of doping and is about ___________________v for silicon
0.6v
how do you overcome the depletion region
0.6V has to be applied to the diode
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
What happens if P-crystal and N-crystal are connected reversed biased
-causes a widening of the depletion area and no current will flow
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
The P type material of a junction has an excess of __________
holes
the majority carriers in P type material are ___________ and the minority carriers are _________________
holes
electrons
A forward biased diode has _________ resistance and a reversed biased diode has _____________ resistance
low
high
The forward break over voltage for a silicon PN junction is about ___________ volts
0.6
In reversed biased the junction tries to block _________ from flowing
current
What happens if you exceed peak inverse voltage
-avalange and diode is destroyed
In an “ideal” silicon diode what would happen when it is forward biased by 0.6V
go into immediate conduction
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
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
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
What happens if the PRV/PIV rating is exceeded and what is it called
-diode will breakdown
-damaging current will flow
-called avalanch current
What are the 2 terminals on a diode called
annode
Cathode
what is a rectifier or rectification
changes AC to DC
how are diodes used to steer current
only conduct when switches are in a certain position
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
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
the lower the ripple frequency % the ___________
better it is
For the % ripple always go by the __________ voltage
output
the average value for one half cycle of an AC sine wave is _____________
0.637 Emax
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
The peak instantaneous voltage in an ac voltage is ___________ times the RMS values. what is the equation
1.414
-PRV= 1.414 x Erms
IF the half wave cct supplies a capacitive load, the diode must have a PRV rating ___________ than ________ the peak line voltage
greater than twice
in a diode the average forward current rating must be ___________ the average current load
equal
Idc=I load
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
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
What does a full wave bi-phase rectifer use for diodes and the transformer?
- the full wave bi-phase rectifier cct uses 2 diodes with a centre tapped transformer
What would happen if both diodes were connected in reverse
output polarity would be reversed
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
The average value of one half cycle of a AC wave form in a Bi phase is _______
0.637 Emax
Each diode conducts for only one half cycle and the average current through the diode will be __________ of the average load current
half
The bridge rectifier cct does not need a centre tapped transformer but does require _________ diodes
4
For a full wave bridge rectifier the output wave form occurs _______ for each input wave form
twice
For a full wave rectifier each diode must have a PRV rating ___________ than the peak of the AC supply voltage
equal or greater
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
the ripple frequency on a bridge rectifier will be ________ the AC line frequency
twice
Hz of the ripple= 2 x Hz ac
what are the 3 applications of capactitors
- charged capacitor as a power supply
- Resistor and capicitor together can be a timing cct
- Capacitors used as filters in rectified DC power supplies to smooth out the pulses of DC and get a higher quality DC supply
what is a capacitor
-charge storage device formed by seperating two conductive “plates” with a dielectric (insulating material)
In a capacitor current stops when the current has _____________
charged to the full supply voltage
A charging time of a capacitor can be reduced by what
-Adding resistance in series with the capacitor
A capacitor opposes changes in ______________
voltage
What happens when the supply voltage exceeds the capacitor voltage
-Capacitor draws a charging current
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
What happens in a capacitor when the supply voltage drops below the capacitor voltage
-capacitor discharges back into the cct
How are commercials capacitors classified
-according to the dielectric
-ex: mica,paper,ceramic, electrolytic
What precaution do you have to use with electrolytic capacitors
-careful with the polarity
What is mica
- a rock
-its a stable material
what happens when mica is used as the dielectric (insulator) in a capacitor
-stable
-reliable
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
advantages of polystyrene plastic film
-high insulation resistance
-low losses
-longer life
How are ceramic capacitors made
earth fired under extreme heat. Very high values
What capacitors provide the most capacitence in the smallest space with the smallest cost
electrolytic
why must electrolytic capacitors must be connected
-applied voltage maintains the positive electrode more positive than the negative terminal
What happens if an electrolytic capacitor is connected with the wrong polarity
-reversed electrolysis forms gas and the capacitor becomes hot and may explode
Ceramic disc capacitors usually have a tolerance of ______________
+- 20%
paper capacitors usually have a tolerance of________________
+-10%
Why is the AC voltage lower for a capacitor
-should be operated close to rated voltage to provide the rated capacitence
What does an RC cct have
resistor and capacitor in series
Why will an RC cct charge a capacitor quicker
lower resistance
Why wont electrons flow through a capacitor
dielectric prevents it
The charging rate (current) ________ as the capacitor voltages approaches the source voltage
decreases
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
How can you determine the charge that any capacitor will take to charge
Q= c x E
How to calculate the time constant in a capacitor
T= R x C
How many time constants does it take to fully discharge a capacitor
5 times
A _____________ frequency Ac, when rectified will provide A better DC than low frequency
high
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
A low percent ripple value is much better than a ____________ percent ripple value
high
What is the percent ripple for a pure DC signal
0%
what does adding a choke do to the cct
choke adds more filtering and creates less filter
What is the max current that a 1k ohm, 1/4W resistor can safley carry?
250 micro amps
What effect does voltmeter loading have on a cct
The voltmeter decreases the voltage across the part of the cct it is connected to
What is created when pure semi conductor material is doped with trivalent dopant?
P-type material
What is created when pure semi conductor material is doped with prevalient dopant?
N-type material
What are the majority carriers in N type material
electrons
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
True or false, Capacitors oppose a change in current
False. they oppose a change in voltage
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
