M3 Flashcards
What does a generator do ?
Separates charges
What is the valence shell
The outer most shell
When an body is in nature what state is it in ?
Natural
What can change the state of an atom
Friction
What do neutrons do ?
Ensure the positively charged protons do not repeal away from negative elections
What is the charge of a electron
-0.1602x10^-18
What is the charge of a proton
0.1602x10^18
What are electrons
A negatively charged partial thats is travelling on various shells
They have an attraction to the charged protons , so do not repeal
What makes up the mass number
Protons and neutrons
What is an ion
A positivity or negativity charged atom
When is an atom neutral
When protons = neutrons
What is a charged atom said to be
Ionised
What is a molecule
2 or more atoms joined together , no electrical charge
What charge does a cation have
Positive
What charge does a anion have
Negative
How are ionic compounds formed
When a cation and an anion are attracted to each other
What are molecules held together by
Covalent bonds
What are ionic bonds held together by
Ionic bonds
What are intermatic bonds held together by
Metallic
What are complex covalent bonds held together by
Coordinate covalent bonds , a mixture of covalent bonds
What is a conductor
Has less than 4 elections in its outer shell , easily losses elections , so can easily conduct
What is a matalic bond
When the atoms are closely packed and have a crystal lattice
What is a conductor
High density , allows the electrons to separate more freely within the atomic structure , high mobility of electrons
Semi-conductor
Has exactly 4 of its valence electrons , very chemically stable , examples silicon and germanium
What is an insulator
Has more than 4 of its valence electrons , tightly packed together, so less electricity can flow through ,
Mica porcelain
What is static electricity
Created be friction , contact , friction , induction
What does grounding an aircraft do
Reduces friction
What happens when a glass rod is rubbed with fur
Becomes negatively charged
What happens when a glass rod is rubbed with silk
Becomes positively charged
What are free electrons
Electrons in the outer shell that get transferred
What happens when an atom gives up electrons
Has a positive charge
What happens when an atom gains electrons
Becomes negative
What is induction
When somthing charged with out contact
What do 2 opposite charges do
Attract
What do 2 like charges do
Repale
What is a force field
Exists around every charged body , the lines of forces extend in all directions from the charged body and terminate where there is an opposite charge
What is Coulomb’s law
The size of the electrostatic force of attraction or repulsion between two point charges
Is directly proportional to the sum of the size of charges
And inversely proportional to the square of the distance between them
What is current
Movement of electrons
What is the equation for current density
J=I/A
Current / cross section area (mm^2)
What is current density
Current will get through the area in the same time regardless of the cross sectional area , the electrons will collide with each other more which will create more resistance and more waste product of heat
What is the maximum temperature of a cable
60 degrees
What is the ambient temperature
25 degrees
What is an electrolight
A conductive liquid
What is electrolysis
The decomposition of chemical compound by passing an electrical current through a liquid , must be an electrolight
What charge has the anode got
Positive
What charge does a cathode have
Negative
What is an inert gas
A gas that’s doesn’t react with any other substance
What are the examples of an inert has
Nitrogen argon and kxypron
How to find resistance in a series circuit
RT= R1 + R2
How do you find resistance in a parallel circuit
RT = 1/R1 + 1/R2
What dose am oscilloscope do
Provide a visualisation of rapidly varying processes in engineering
What is the difference between oscilloscopes and oscillograph
Oscillograph permanently recorded and the other isn’t
What is potential difference
The voltage between two different charged points
What dose a generator do
Draws electrons from the positive pole and transports them to the negative pole in a way where the potential difference is maintained
What are electric flux lines
The force field around a charged body takes the shortest path , from the positive side to the negative side , the density of the flux Lines represent the quality of the electrical extraction between both charges
The more flux lines the more field strength there is
The more flux lines the more stronger the attraction is
What is EMF
The electromotive force , is the field strength between two points , will not arise unless two fields act on one another
What is polarity
Is what makes A/c and d/c different
D/c didn’t change polarity
A/c dosent change polarity
What is voltage
The difference between electrical charges or potential
What happens to the electrical attraction and potential energy in the valence shell
The electrical attraction is weak
Potential energy is strong
Opposite to each other
What is the equation for ohms law
V=IxR
Direction of current flow in a circuit
Outer part - negative to positive
Inner part - positive to negative
What is conventional current flow
Positive to negative
What is electron flow
Negative to positive
What is resistance
The opposition to current flow
Measured in ohms
What dose resistance do
Applies a breaking force to the circuit slows down movement of current
What is the relationship between conductance and resistance
High resistance - low conductance
Low resistance - high conductance
Inversely proportionate
What is the equation for conductance
Conductance (G) = 1/R
Measured in Siemens (S)
What is the equation for charge
Charge = current x time
Q = I x T
Measured in coulumb (C)
What is the charge of an electron
1c = 6.24x10^18
What are examples of semi conductors
Silicon gallium
What is emf
Difference between two points of voltage charge
What is Induction
Charging somting while no touching it
When do semi conductors change there properties
With light voltage or heat
What is doping
The addition of international impurities into a semi conductor to alter its properties , to make it more elective
How dose a Filment bulb work ?
The elections are realised touch the phrpspus coating and break into 2 , this creates exponential growth more electrons , so they begin to hit each other , hits and creates a uv light
Electricity due to light
N-type material negative
P-type material positive
Opposite charges attract They try to get to each layer Boundary layer stops one flow More atomic vibrations , more quicker they will move creates heat Creates light Creates a current flow
Electricity due to heat
In a metal the valence Electrons diffuse as mike charges to repel
A force is added heat with results in elections having more potential emergy and separate form the metallic bond , called emissions
Electricity from Friction
When an insulator is rubbed the electrical charges are separated and voltage is separated
Two bodies with a difference charge have a voltage and a electrical field around them
If the electrical field gets too strong , electrons more through the insulating air toward the positively charged body
The electrical field is concentrated at its edges , so sparking will occur , this is the reason for static discharge
What is a piezo crystal
A crystal that’s can be deformed from pressure and a voltage and be generated , called piezoelectric effect
Where is piezoelectric effect used
Record players Microphones Loudspeakers Lighters Pressure gauges Dynamometers
Voltage generation by electrochemical series
A voltage occurs between a metal and a electrolyte
The higher the distance between both substances of the galvanic cell in the series the higher the voltage between them in the electrolyte
Generation of electricity in magnetism and motion
If a coil enters the magnetic field of a magnet, an electrical voltage is generated in the coil during the movement
What is inductance
If a coil enters the magnetic field of a magnet, an electrical voltage is generated in the coil during the movement
What is a primary cell
Primary cells can immediately supple voltage without charging them before hand
The cannot be charged , so cannot be reused
Eg zinc-carbon-battery
What is capacity
The quality of electrical charge measured in Ah
What is a secondary cell
Can be recharged
Used in aircrafts and all devices
What is the voltage of a lead acid cell
2V
What is the finial discharge of a leaf acid cell
1.83 volts
What is the positive plate in a lead acid cell made of
Lead peroxide (bpO2)
What is a negative plate in a lead acid cell made of
Pure spongy lead
What is the liquid electrolyte made of in a lead acid cell
30% sulphuric acid
70% water
How do lead acid cells work
Doing discharge the slulphuric acid breaks up into the hydrogen ions with a positive charge , sulphate ions with a negative charge
Sulphate ions combine negative plate form lead sulphate
Create excess of electrons on negative plate
Hydrogen ions go positive plate combine oxygen form water
The positive plate has a deficiency of electrons
Negative plate has a excess
Plates are connected by conductor conventional current flows both plates coated in lead sulphate battery is discharged
The charging process of a lead acid cell
Current is passed through the storage Battery in the election flow direction
The sulphate ions are driven back into the soloution in the electrolyte where they combine with the hydrogen ions of water , thus forming sulphate acid
The plates return to there original composition lead peroxide and spongy lead and the battery is said to be charged
What is the voltage of a nickel cadmium cell
1.2V
What are the plates made of in a nickel cadmium cell
Positive plate - nickel oxyhydroxide
Negative plate - metallic cadmium
Discharging in nickel cadmium cell
Hydrogen ions from the electrolyte combine with the negative plates and the electrons are released to the plates cadmium is converted to cadmium hydroxide
Hydroxide ions from the positive nickel oxyhydroxide
Plate to electrolyte
So electrons are delivered to the negative plate from the postive plate
Advantage of nickel cadmium cell
Better power to weight ratio
Closed circuit voltage
Lower discharge
Disadvantage of nickel cadmium cell
More costly
Larger
What is a mercury oxide cell
Postive plate - mercury oxide Negative plate - zinc powder Electrolyte - lime potash Voltage rated - 1.35v Constant internal resistance during discharging Constant voltage during operation
Silver oxide coin cells
Contain silver oxide , line potash , and zinc
Have a high energy density
Low voltage depression
Rated voltage is 1.55V
Lithium coin cells
High rated voltage up to 3.5V
High energy density
High lifespan
Used for pacemakers , cameras
What is the current in a series circuit
The same at all points
What is the voltage in a series circuit
The total voltage of equal to the total voltage at all points in the circuit
What is the resistance in a series circuit
RT = R1 + R1 …
What is the resistance in a parallel circuit
Lower than the lowest individual resistance
The current in a parallel circuit
The total current is the sum of the individual currents
The voltage in a parallel circuit
The voltage remains Constant, the voltage across branches is constant
What is the Short circuit current limited by
Interval resistance
What is a shirt circuit limited by
Internal resistance
What is a battery’s interval resistance
Equal to the difference between the open circuit voltage and the closed circuit voltage divided by the applied load
What is a thermo couple
Two different metals are connected at one end by soldering
There junction is heated and a voltage is generated between the two free ends
Called thermoelectric voltage
What is the temperature range of a thermo couple
-200 to 2300
What happens when a photo cell is exposed to light
A voltage is generated
What dose a photo cell consist of
Matalic base plate with a good conductivity which is attached to a semi conductor layer
A thin translucent metal skin is vaporised onto this layer as a counter electrode
How dose a photo cell work
Exposure to light releases electrons from the semiconductor layer, which then flow to the metal skin. Thus, the base plate is positively charged and the metal skin negatively charged, hence a voltage is generated.
What factors effect photo cells
Light intensity
Kind of light
Depletion
What voltage do photo cells produce
0.6v
What is phase
The position of a point in time
What is the period
The time it takes to perform one cycle
What is frequency
The number of compete cycles , oscillations per second
What is the equation for frequency
Frequency (F) = 1/ cycle time (t)
Measured in hertz
What is the equation for power
P=IV
What is the peak value of a wave
The amplitude
Measured from zero
Unit either volt or amp
What is a mid ordinates of a wave
The equally divided portions
What is the average of a wave
Va = sum of all the mid-ordinates
Number of mid-ordinates
What is the rms
Root mean square
The value of a alternating current is the value which applies to the same resistance will produce the same power as an equivalent DC
How do you get from A/C to D/C
X by 0.707
How do you get from D/C to A/C
X 1.414
What angle is the displaced coils at in the 3 phase system
120
In phase what happens to the load
There are symmetrical and equally balanced
Why is a multi-phase used
It generates greater quantities of power than a single phase transmission systems
How is a multi phase system be constructed
Three coils are attached to a the Stator
Voltage is generated in each coil
A moving coil voltmeter is attached with zero point is in the middle of the scale
The three will point one left and once to the right during one revolution
When rotating an ac voltage is induced all
Voltages have the same magnitude
Form the phase winding of the generator, in each a voltage is generated
The coils supply 3 separate single phase ac circuits
What is the phase referenced to ground
115V
What is phase to phase in an aircraft
200V
What is a advantage of 3 phase
Two different voltages can be measured
When will nothing be flowing in a nutral line
If all three phases have the same loading and there is no phase shift in the circuit
When where there be current flowing in the neutral line
If there is a complete inblance in the three loads but they are real loads then a current will flow equal to the current in one phase
Why can’t you connect all three phase together
Will create a shirt circuit to the generator
What is the 3 things that effect inductance
The size of the coil
Relative movement
Strength
