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ATPL AGK > Electrics > Flashcards

Electrics Flashcards

1
Q

What is conventional flow

A

Electrons flow positive to negative

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2
Q

What is a coulomb

A

Quantity of electrons

6.25 x10^18 electrons

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3
Q

What is a ampere

A

Unit of current is the rate as which electrons flow within the conductor

Coulombs / second

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4
Q

What is 1 ampere

A

1 coulomb passing a point in a conductor in one second

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5
Q

How is a ammeter connected in a circuit

A

Series

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6
Q

What is EMF

A

Electromotive force (potential difference)

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7
Q

What is 1 volt

A

Magnitude of emf that causes 1 coulomb to move from one place to another

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8
Q

How is a volt meter connected in a circuit

A

In parallel

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9
Q

What is 1 ohm

A

The amount of resistance that will allow one ampere of current to flow in a circuit to which one volt of EMF has been applied

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10
Q

What is specific resistance

A

Resistance of a cube of material at 0°c

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11
Q

What happens to resistance with temperature increase

A

Resistance increases = positive temperature coefficient (PTC)

In a few materials that resists decreases = negative temperature coefficient

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12
Q

What is the unit of conductance

A

Siemen

1 siemen is a ohm^-1

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13
Q

What factors determine resistance

A

Specific resistance (p)
Length (l)
Cross sectional area (A)

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14
Q

What happens to resistance with increase in length

A

Resistance up

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15
Q

What happens to resistance with increase in cross sectional area

A

Resistance decreases

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16
Q

What is ohms law

A

1 volt causes a current of 1 ampere with a resistor of 1 ohm

V=ir

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17
Q

What is Kirchhoff’s first law

A

Sum of currents entering a junction must equal the sum of currents leaving a junction

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18
Q

What is Kirchhoff’s voltage law

A

In any closed circuit

The cum of voltage drop equals the supply voltage

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19
Q

What is power

A

Rate at which work is done (watts)

One volt causes one ampere to flow one watt is consumed

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20
Q

What is the equations of power

A

P=VI

P=I^2xR

P= V^2/R

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21
Q

What is the principle of a Wheatstone bridge

A

If all resistors are the same = potential difference is 0

If the variable resistor heats up = there is a potential difference

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22
Q

What is a single pole / uni pole / earth return system

A

Uses aircraft skin / surface as conductor / wiring

Reduces resistance

Reduces weight by almost half

If bad weight due to loose screws = possible faults

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23
Q

What is a dipole / two wire system

A

Everything connected with wires

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24
Q

What is a short circuit in a single pole earth return system

A

Live conductor touches metal airframe

Very low resistance = very high current

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25
What is a short circuit in a dipole system
It both conductors tough each other
26
What is a open circuit
If conductor breaks / disconnected
27
How are fuses rated
In respect to their current Fit a fuse slightly above current P=IV
28
How many fuses need to be carried on board a flight
At least 10% the fuses of each eating or 3 of each rating whatever is greater
29
What is a current limiter
Just before buss bar to trip for very high voltages
30
What is a non trip free push pull circuit breaker
Pops out if circuit too high Heats a thermal element = pops breaker = stops current flow You could hold in breaker to keep current flow
31
What is a trip free circuit breaker
Pops if current too High Heats a thermal element Secondary contact stops you holding in breaker
32
What is the disadvantages of standard thermal circuit breakers
Heating takes time = can have short periods of overload
33
What is the principle of a magnetic circuit breaker
Current through wire = magnetic field Excessive current = bigger magnetic field = pulls breaker magnetically Provides instantaneous protection for components that are too sensitive to tolerate prolonged overload
34
What is the disadvantages of all circuit breakers
Can be worn over time = trip too easily
35
How many times should a circuit breaker be reset
Once
36
Can a circuit breaker be used as a switch
No Only as part of abnormal situations (emergency drill procedure)
37
What is a rocker switch
Like a standard light switch
38
What is a push switch
Push to switch on, push to switch off Nah have illuminated message on switch
39
What is a inductive proximity switch
When 2 magnets close to each other No physical moving parts
40
What is a rotary switch
Can be progressive or selector of different functions
41
What is a toggle switch
May have 2/3 positions Positive action = pull out switch to move Guarded switch = slip a hard before switch = for one off operations
42
What is static electricity
2 surfaces have contact with one surface having a lower resistance = excess positive charges on one material Can be caused by: Friction on skin / propellers Lightening Electrical circuits / equipment
43
What are bonding strips
Ensure a uniform electrical potential across the airframe Reduces static interference
44
What is cable screening
Helps reduce / prevent external interference
45
What are static discharge wicks for
Discharge any static electricity that builds up in airframe during flight
46
What is a battery
A chemical reduction / oxidation reaction occurs at 2 electrodes which are separate by a conductive electrolyte Reduction reaction at cathode Oxidation reaction at anode Electrons re enter battery at cathode
47
What is a primary cell
Non rechargeable Mainly emergency lighting Carbon zinc cells
48
Secondary cell
Rechargeable Main batteries in aircraft Lead acid / nickel cadmium Lead acid battery uses sulphuric acid
49
When a single lead battery is used what is its specific gravity and voltage
Fully charged: Voltage 1.27v Specific gravity 1.27 Fully discharged: Voltage 1.8v Specific gravity 1.1
50
What is the terminal and nominal voltage of a batter with 6 cells at 2.2 volts
Terminal voltage 13.2v Nominal voltage 12v Lead acid battery output voltage drops steadily
51
What type of battery is a alkaline battery
Uses potassium hydroxide Ni-CAD
52
What is the volt and specific gravity of a alkaline cell
Required 10 cells for a 12 volt battery 1 cell = 1.3 volts fully charged Fully discharged 1.1volts Specific gravity remains constant
53
In a alkaline battery what is the terminal and nominal voltage
Terminal voltage with 10 cells = 13volts | Nominal = 12volts
54
What is the voltage trend for a discharging ni-cad battery
Voltage remains consistent for longer time period
55
Lithium - ion battery
No memory effect | Slow loss of charge when not in use
56
What is a non spill vent
Blocks battery vent at any attitude other then level to stop spill of hydrogen Hydrogen normally vented to atmosphere
57
How to deal with acid spillage
Neutralise with bicarbonate of soda
58
How to deal with alkaline battery spillage
Neutralise with boric acid
59
What is a sealed battery
Used in some small aircraft Does not emit corrosive gasses during charging Will not spill it tipped Needs special charger
60
What is a battery measured in
Ampere hours Depends on size and number of plates
61
How often if s battery checked
3 monthly intervals Min capacity = 80% of rated capacity
62
How does temperature affects capacity
-10°c may reduce capacity to only 10% of its rating Some aircraft have thermal blankets Some charge constantly to keep them warm
63
How are alkaline battery’s charged
High rate of charge at low voltage Once voltage is higher = pulse charge To stop thermal runaway
64
What is thermal runaway
I’m alkaline batteries resistance decreases with heating Temp increases Resistance decreases Current increases Temp increases etc Serious risk of fire
65
How long does a main battery need to last with total electrical failure
Must last at least 30 mins
66
How long must the emergency lighting batteries last in total electrical generating systems
Must last for at least 10 mins
67
How does a battery in series affect voltage and capacity
Increases voltage Capacity remains the same
68
How does batteries in parallel affect voltage and capacity
Increases capacity | Voltage remains the same
69
Practical application of electromagnetism
Can control but circuit with little switch =. Relay
70
What is a relay
Has a hinged arm and one set of contacts
71
What is a solenoid
Has moving core and two sets of contacts
72
What is a contractor
Mechanically latched solenoid
73
What is a dc generator (Dynamo)
Produces dc output
74
What is a dc alternator
Produces ac output which is then rectified to dc
75
What is faradays law
Amount of emf induced depends on: Strength of magnetic field Speed of conductor relative to field Angle at which conductor cuts the field Length of conductor in the field
76
What is a commutator
Turns ac into pulsed dc
77
Multi segment armature
More loops and more commutators = reduces pulse
78
What is a carbon pile voltage regulator
Has a carbon pile (variable resistor) in series with electromagnet Aim for output to be 112% of battery output to recharge battery
79
How does a carbon pile work
``` When crushed less resistance More current More magnetic field Higher voltage ``` This gets fed to another electromagnetic coil This is under the carbon pile to stretch it Increases resistance Less current Self regulates voltage
80
What is a differential cut out
Creates gap / illuminated red power failure warning lamp when generator voltage drops below battery voltage
81
What is a busbar
Basically extension lead
82
Which hand rule of Flemings does what
Motor = left Generator = right
83
What is back emf
When conductor of motor moves in a magnetic field a voltage is generated in the conductor Direction of this generated voltage always acts in opposition to the supply voltage
84
What is a series wound motor
High starting torque and are used on aircraft as starter motors and actuators
85
What is a shunt wound motor
Low starting torque used where a fairly constant speed is required Eg. Windscreen wipers, fuel pumps
86
What is a starter generator circuit
Once engines started = no need for started motor Then is used as a shunt wound generator
87
How to change direction of rotation of motor
Change direction of current Change polarity of magnetic field
88
What is a actuator
High speed reversible series wound motors who’s output is normally converted into driving torque via a step down gearbox
89
What is a rotary actuator
Rotary movement usually used for rotary valves in air conditioning Hydraulic, fuel systems
90
What is linear actuators
Driven directly from reduction gearbox via lead screw that extends / retracts a ram / plunger
91
What is a friction clutches
Incorporated in transmission systems to protect against mechanical over loading Usually single played / multi plate type depending on size of actuator
92
What is a electro magnetic brakes
Prevent over travel / creep when motor switched off Held on with a spring and help off when motor is operating by electromagnetic solenoid
93
What is a dc alternator
More efficient than generators Ac output needs to be rectified to produce dc
94
What is a half wave rectification
Turns ac into one half of a ac = dc
95
What is three phase ac generator
3 overlapping wave forms Rectified with diodes
96
What is a centre reading ammeter
Shows what batter is doing Ammeter between battery and busbar
97
What is loadmeter
Ammeter between alternator and busbar Only shows current / work done by alternator
98
Inductance
Property of a device or circuit which opposes a change in current flow 1 Henry = amount of inductance which will include and emf of 1 volt in a conductor when the current changes at a rate of 1 amp per second
99
What is a inductor
Oppose changes in current flow and therefor offer opposition to alternating current flow Inductance characteristics can be increases by; - increasing number of turns on the coil - inserting a piece of soft iron into the coil
100
What is capacitance
Property of an electrical component which is able to store energy in an electrostatic field Device which stores energy in this manner = capacitor (condenser) Unit of capacitance = Farad (F) One farad = amount of capacitance that will store a charge of one coulomb when an emf or one volt is applied
101
What is the formula for capacitance
C is proportional to KA/d Capacitance = c Area of plates = A Distance between played = d
102
Advantages of AC
Can be efficiently changed from one voltage to another using a transformer Ac generators are lighter Efficiently changed into dc using rectifier
103
What is the root mean squares voltage (rms)
0.707 x peak ac voltage Has same heating effect as the same value of dc
104
What is periodic time
1/ frequency
105
Usual aircraft electrical frequency
400hz
106
What is capacitive reactance (Xc)
Capacitor constantly charging and discharging Because of time lag = voltage across capacitor is in constant opposition to supply voltage Inversely proportional to supply frequency
107
If a circuit is purely capacitive ac, what is the voltage / current lag
Voltage lags the current by 90°
108
What is inductive reactance (XL)
Counter end induced into an inductor by the varying current = opposes the supply voltage Proportional to the inductance of the inductor and frequency of the supply voltage
109
If a circuit is purely inductive ac, what is the voltage / current lag
Current lags the voltage by 90°
110
What is impedance (z)
Total opposition to current flow in a ac circuit Vector sum of inductive reactance, capacitive reactance, and resistance
111
What is the formula for impedance (z)
Z = *squareroot* (R^2 + (XL-Xc)^2)
112
If frequency increases what happens to Xc and XL
Xc decreases | XL increases
113
What is resonant frequency
When XL=Xc
114
What is the power rating of Ac generators
Kilovolt-amperes (KVA)
115
What is a apparent power
Real power + reactive power RMS voltage x RMS current
116
What is true power (effective / real power)
Power consumed by the resistive components in the circuit (watts) RMS voltage x RMS current x power factor
117
What is reactive power (watt less power)
Is that consumed by the reactive components Unit is volts - amperes reactive (VAR) Amount of power required to overcome reactance
118
What is apparent power
By multiplying voltage and current together Unit = volt ampere (VA)
119
What is power factor
Amount of power consumed in the ac circuit True power / apparent power If voltage and current are in phase then power factor = 100%
120
A transformer allows the passage of
Ac but blocked dc
121
As voltage increases through a transformer what happens to current
Decreases
122
A transformer rectifier unit
Ac to dc If little power demand will head up = requires cooling fan
123
Inverter does what
Converts dc to ac voltage
124
What are the 2 main parts of a 3 phase ac generator
Rotor which carries the electromagnetic field Stator which carries three pairs of phase windings
125
Advantages of 3 phase ac
Higher efficiency Fewer conductors required for distribution Three phase motors have better characteristics than single phase Same source can be used for single phase and three phase
126
What is phase voltage (Vp) in a star / y connector
Potential difference from each phase to a neutral point
127
What is line voltage (Vl) in a star / y connector
Potential difference across any two lines
128
What is the current for a star connector
Line current = phase current
129
If there is a oil leak in a constant speed drive unit (CSDU) what happens to pressure and temp
Oil pressure decreases | Oil temp increases
130
What is a generator control unit
Voltage regulation Frequency control Protection circuits Controls differential protection
131
What tolerance must the voltage be within for paralleling of ac generators
110-120v
132
What tolerance must the frequency be within for paralleling of ac generators
395-405hz
133
What must be in sync for the paralleling of ac generators
Voltage Frequency Phase frequency Phase displacement
134
What is a persistent fault
One that continues one BTB’s have been opened
135
What is real load to do with
To do with torque
136
What is real load sharing to do with
Achieved by a load sharing loop adjusting magnetic trim in mechanical governor of the CSDU’s simultaneously via load controllers within the GCU’s
137
What is reactive load factor
Achieved by a load sharing loop adjusting the excitation of the paralleled generator fields simultaneously via the voltage regulators within the GCU’s
138
What does a RAT do (ram air turbine)
Propeller drives hydraulic pump which in turn drives ac generator at a constant speed to deliver 115/200v 3 phase 400hz
139
What is a semi conductor
Resistive in natural state but can be doped Typical material is silicon / germanium
140
What is semiconductor doping
Adding materials with less or more electrons Adding materials with more = more electrons can flow
141
What is a forward bias semiconductor
N-type connected to negative terminal of a emf supply Electrons flow easily = current flow
142
What is a reverse bias semi conductor
Electrons pulled away from junction | = no current flow
143
What is a zener diode
Allows reverse current flow after a certain voltage has been achieved Used in voltage regulators as protection device for voltage sensitive equipment
144
What is a transistor
Sandwich of P and N type materials
145
What is a AND gate
All or nothing
146
What is a OR gate
Either supplies | Or both
147
What is a NOR gate
Anything from any signal switches it off
148
What is a NAND gate
Give a 1 output when the AND gate would not
149
What is a NOT gate
Any input = no result
150
What is a exclusive OR gate
Only works if either A or B not both

ATPL AGK (3 decks)

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