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ATPL > AGK - Electricity > Flashcards

AGK - Electricity Flashcards

(95 cards)

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1
Q

What is current?

A

Charge over time

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2
Q

How do electric field lines flow?

A

Out from positive

In toward negative

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3
Q

What is coulomb’s law?

A

The strength of the electric force/field can be increased by

increasing the amount of charge
decreasing the distance between charges

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4
Q

What is Kirchoff’s 1st law?

A

Total current flowing into a point must be the current flowing out of that point.

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5
Q

What is Kirchoff’s 2nd law?

A

The sum of the voltage drops of a circuit must equal the emf.

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6
Q

Which factors affect resistance?

A

Length - Proportional
Cross-sectional area - Inversely proportional
Material
Temperature - Proportional

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7
Q

Resistors in series?

A

Add resistances together

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8
Q

Resistors in paralell?

A

1/Rt = 1/R1 + 1/R2 + 1/R3 …

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9
Q

What is a pole?

A

The connector

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10
Q

What is throw?

A

Moving from 1 position to another

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11
Q

Another name for push switches?

A

Light switches because they have lights in indicating condition.

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12
Q

What is momentary and alternative action on a switch?

A

Momentary - only while holding

Alternate - Toggle

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13
Q

What does a thermo switch do?

A

Make or break circuit when it reaches certain temps

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14
Q

What is a unipole system?

A

Old aircraft using ground as airframe.

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15
Q

What is a dipole system?

A

Composite aircraft have a return wire to ground.

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16
Q

What is a non-trip free circuit breaker?

A

Old type of breaker where the button can be pushed in again to complete the circuit even if the fault still exists.

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17
Q

What is a trip free circuit breaker?

A

Trip free circuit breaker prevents current from returning if the button is held in and the fault is still present through the use of secondary contacts.

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18
Q

What are thermal circuit breakers used for?

A

Protected circuits in event of prolonged over current.

Through use of two bitmetallic strips with two different coefficients of expansions

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19
Q

What is a magnetic circuit breaker and what is it used for?

A

A magnetic circuit breaker uses current instead of heat to generate a magnetic field to pull the breaker at a very specific point.

They are used in sensitive circuits where there is no delay and strict current limits.

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20
Q

How many spare fuses must an aircraft carry?

A

10% of number of fuses which use that specific rating
3 of each specific rating of fuse

The higher of these 2 values.

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21
Q

What are current limiters? (4 facts)

A

Allow short term overloads
High current fuses
Cannot be changed in flight
Normally found in series with busbars

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22
Q

How is static electricity generated?

A

Rubbing and friction exchanging electrons

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23
Q

What is a static discharge wick?

A

Static electricity likes sharp discharge points, a wick is a sharp discharge point which can be used to dissipate static electricity back into the atmosphere from the airframe.

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24
Q

Where do we find out how many static discharge wicks we can lose?

A

The Minimum equipment list (MEL)

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25
What is bonding?
Bond each part of the airframe together to allow a low resistance path between all parts of the airframe and the static wicks. Allows a uniform potential across the airframe.
26
What is grounding?
Airframe can still have charge after landing. Ground to prevent arcing from fuel nozzle and prevent fire.
27
Why are cables covered in protection screening?
Wires carrying current have magnetic field. This can interfere with other circuits. Shield prevents this.
28
What is in a cell?
Anode (-) Cathode (+) Electrolyte separating them
29
How is a primary cell different to a secondary cell?
You can't recharge a primary cell
30
Why is a secondary cell different to a primary cell?
You can recharge it
31
What are the two types of secondary cell?
Lead Alkaline (NiCad) The ELECTROLYTE determines the type!
32
What is the electrolyte in a lead acid battery?
Dilute sulphuric acid
33
What is in a lead acid battery
Anode - Lead peroxide Cathode - Spongy lead Electrolyte - Dilute sulphuric acid
34
What is the terminal voltage of a lead acid cell?
2.2 V
35
What is the nominal voltage of a lead acid cell?
2 V
36
What is terminal voltage?
Voltage of battery/cell off load
37
What is nominal voltage?
Voltage of battery/cell on load
38
What is the terminal voltage of a lead acid battery?
13.2 V (off load)
39
What is the nominal voltage of a lead acid battery?
12 V (On load)
40
How many cells in a lead acid battery?
6 Cells (2.2 V Term, 2 V nom)
41
What does the voltage of a battery/cell depend on?
Material and not size
42
Characteristics of lead acid discharge?
Voltage drops off gradually with discharge Think of dimming torch
43
What is Sulphation?
Lead acid battery suffers from sulphites blocking pours in the cathode (spongy lead) preventing charging of the battery. Occurs when left discharged for a long period.
44
How do we prevent sulphation of lead acid batteries?
Store them fully charged
45
What is specific gravity?
Similar to density
46
What is the specific gravity of a charged lead acid battery?
1.27 SG
47
What is the specific gravity of a discharged lead acid battery?
1.17 SG
48
How many cells in NiCad battery?
10
49
NiCad terminal cell voltage?
1.3V
50
NiCad nomimal cell voltage?
1.2V
51
NiCad battery terminal voltage?
13V
52
NiCad battery nominal voltage?
12V
53
Discharge characteristics of NiCad?
Alkaline batteries - Bright torch Voltage drops slightly with charge, remains constant then drops off suddenly.
54
What happens to NiCad specific gravity with charge?
Doesn't change.
55
How is a battery connected with a generator to charge it?
In paralell.
56
Why does generator produce higher voltage then battery?
So when generator is running, forces current into the battery charging it.
57
What is a NiCad thermal runaway?
In NiCads resistance decreases with temperature Temp increases -> Resistance decreases -> Current increases -> Temp increases more
58
How do we stop NiCad thermal runaway?
Monitor the temperature of the battery and adjust current accordingly.
59
What do we clear up lead acid electrolyte spillage with?
Acid electrolyte | Alkaline - Bicarbonate of soda
60
What do we clear up NiCad spillages with?
Alkaline electrolyte | Acid - Boric Acid
61
What is the electrolyte in a NiCad?
Potassium hydroxide
62
What do we measure battery capacity in?
Amp-hours
63
How are battery capacities tested?
At 1 hour rate. I.e current discharging battery in an hour So 25 Ah battery would be 25 Amps for an hour.
64
How does battery capacity change in series?
It doesn't | Voltage changes but capacity same
65
How does battery capacity in paralell change?
Add together the capacities of the batteries
66
What happens to capacity of a battery in lower temperatures?
It goes down
67
What is the minimum capacity of a battery?
80%
68
How long must main batteries last (CS25)
30 Minutes
69
How long must emergency light batteries last? (CS 25)
10 Minutes
70
What demagnetises a permenant magnet (2 things)?
Heat | Vibration
71
How do we find field direction in a coil electromagnet?
Right hand rule Fingers are field direction Thumb is current direction
72
What 3 things strengthen electromagnets?
Current Number of coils Soft iron core
73
What is a relay?
Low voltage control circuit operates electromaget switch to high voltage operating circuit. Fixed core single contact EM switch allowing remote control of heavy loads
74
What is a solenoid?
Have a moving core with twin contacts | Heavy duty loads
75
Why is a relay different to a solenoid?
Relay light duty device Solenoid heavy duty device Relay has a fixed core
76
What is a contactor and how is it different to a solenoid?
The contactor latches on/off and stays in position unlike a solenoid. Will not move until powered up again
77
What is Lenz's law?
The current generated in a conductor produces it's own magnetic field which opposes the field creating the current.
78
When do we use the right hand rule (FBI)?
Generators
79
When do we use the left hand rule (FBI)?
Motors
80
How does a DC generator create DC from the AC output in the armature?
It uses a split ring commutator
81
What is an armature?
Where we induce an emf (drive current)
82
Why is it bad to rotate the armature?
The armature is where we generate electricity and to extract this we will need to use brushes with rings to extract it, high currents will pass through these brushes causing wear.
83
What is the difference between a DC generator and alternator?
The alternator has a rotating field and a fixed armature.
84
How do we convert AC in the armature to DC in a DC alternator?
Bridge rectifier
85
What happens to the series wound field in a DC generator?
As load and current increases, current increases and so does field
86
What happens to the shunt wound paralell coil in a DC generator with load?
Emf stays constant even with load | But output goes down with load as current varies
87
What is a compound wound field?
Use both effects of series and shunt coils to smooth out voltage and excitation field drops in DC generator.
88
What is the purpose of a voltage regulator on a DC generator?
We place it in series with the shunt coil, it is a variable resistor which senses the voltage of the output and controls current through the shunt coil/field.
89
What do you monitor on your DC electric system?
Monitor Voltage and Current
90
Two types of voltage regulator?
Carbon pile, vibrating contact
91
What does a current regulator in a DC generator do?
Opens contact to field coil to prevent overload
92
How does DC generator overvoltage work and why is it needeD?
Electromagnet sense overvoltage cutting contacts to field coil and disconnects the entire generator. Now just rotating armature. It is required because overvolting can cause electrical components on the aircraft to be damaged.
93
What is the reverse current cut out relay used for on a DC generator?
Protects you in the event the generator voltage drops lower than the battery, this stops the battery driving the generator.
94
In a system with 2 DC generators, what does the Differential cut out prevent?
If there is a larger than 2 voltage difference between the two generators, it removes one of them to prevent it doing all the work and going past it's rating.
95
In a system with 2 DC generators, what does the equalising circuit/load sharing circuit do?
It fine tunes generator voltage regulators to balance field coil and generator voltages to get the same voltage out of both generators.

ATPL (5 decks)

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