1
Q
Define heat?
A
Transfer of energy due to a difference in temperature
2
Q
Define temperature?
A
Measure of hotness or coldness of an object
3
Q
Define thermal energy?
A
Amount of total energy an object contains due to the kinetic motion of its particles
4
Q
Four different temperature scales?
A
- Celcius - Most commonly used scale
- Kelvin - Scientific measurements
- Fahrenheit - Commonly used in the USA
- Rankine - Mechanical engineering
5
Q
Define absolute zero?
A
- Theoretical lowest possible temperature that can be achieved
- The point at which all atomic motion is assumed to stop and kinetic energy is zero
6
Q
Temperature scale commonly used for mechanical engineering?
A
Rankine
7
Q
Temperature scale commonly used for scientific measurements?
A
Kelvin
8
Q
How does a liquid thermometer work?
A
- A the temperature rises, the liquid heats up and expands through thermal expansion - thus rising in the tube and indicating the temperature
- Temperature is read upwards
9
Q
How does a gas thermometer work?
A
- When heated, the air expands and pushes the water down the glass tube
- When cooled, the air contracts and the water rises
- Temperature is read downwards
10
Q
Define thermocouple? How does it work?
A
2 pieces of dissimilar metal wires form a circuit where the 2 junctions are hot and cold (when one is heated, the other is kept at room temp), this creates an electromotive force and the current begins to flow
11
Q
How does a resistive thermometer work?
A
- Costant current is pushed through resister
- Resister placed in area that you want to measure the temperature
- As temp increases, the resistance also increases slowing the current down
- The difference in current is used to calculate temperature
12
Q
Define heat transfer via convection?
A
- Process of heat movement that happens inside a fluid, as the fluid heats, it expands and becomes less dense - this creates buoyancy
- Displaced air / fluid - The cooler air / fluid at the top is forced to the bottom to create circulation
13
Q
Define heat transfer via radiation?
A
- Does not require a medium to travel
- Transfers heat via electromagnetic radiation and travels through the vacuum of space
- Transfers in waves at the speed of light
14
Q
Define heat transfer via conduction?
A
- Must be touching to have heat transfer
- Vibration of hot particles are transmitted via contact to the colder particles, making them all vibrate quicker
15
Q
Can heat generated by conduction and convention travel through a vacuum?
A
No
16
Q
If the kinetic energy between 2 substances is shared, what will happen to the temperature of the substances?
A
Thermal equilibrium will be achieved
17
Q
First law of thermodynamics?
A
The increase in the energy of a thermodynamic system is equal to the amount of heat added to the system, minus the work done by the system on the surroundings
18
Q
Equation for the first law of thermodynamics?
A
Change in internal energy = heat added to the system - work done by the system
19
Q
Second law of thermodynamics?
A
- When energy is transferred from one form to another, entropy increases and energy decreases
- No process is 100% effective
20
Q
Define entropy?
A
The measure of disorder in a system - randomness
21
Q
Equation for work done by expanding gases?
A
W = f x s
Work done = force x displacement
22
Q
Example of work done by expanding gasses in aerodynamics?
A
Gas turbine engine
23
Q
How is specific heat of a gas at a constant pressure different to specific heat of a gas at constant volume?
A
Constant volume: all heat energy is used to raise the energy of the gas and its
temperature
Constant pressure: All heat energy causes the gas to expand (to do work), not all of the heat energy is being used to raise the temperature
24
Q
Term given to the simplified version for gas behaviour?
A
Ideal gas laws
25
What is an Isothermal process?
Explain the proportionality equation?
Another name for this process?
Iso - Constant
Thermo - Temperature
Define Boyle's law
- Maintaining / locking the temperature
- When the volume remains the same, but space changes, the pressure changes
Volume increase = pressure decrease
Volume decrease = pressure increase
26
Isobaric process?
Explain the proportionality equation?
Another name for the process?
Charles' law -
Locking pressure (directly proportional)
REMEMBER: King Charles singing under pressure
Volume increase = temperature increases
Volume decrease = temperature decreases
27
Explain an isochoric process?
Explain the proportionality equation?
Provide another name for this process?
Pressure law - also known as Gay-Lussac's Law (nothing to do with pressure)
Iso - Constant
Choric - Volume
- Locking volume
Temperature increase = pressure increase
Temperature decrease = pressure decrease
REMEMBER - Gays are loud
28
Define the general gas law?
Pressure x Volume = Temperature (at constant volume)
PV=T
29
Define adiabatic processes?
No heat enters or leaves the system
30
What happens to the temperature and pressure during adiabatic compression?
Increase in temperature and pressure
31
What happens to temperature and pressure during adiabatic expansion?
Temperature of the gas will decrease
32
Engine cycle - in correct order - for an internal combustion 4 stroke engine?
- Intake
- Compression
- Power
- Exhaust
33
Describe the engine cycle for an internal 4 stroke combustion engine?
Suck, squeeze, bang, blow
1) The piston is pulled down inside the cylinder by the momentum of the crankshaft. The inlet valve opens, sucking in a mixture of fuel and air into the cylinder
2) The inlet valve closes, the piston moves back up the cylinder and compresses the fuel-air mixture.
When the piston reaches the top of the cylinder, the spark plug fires
3) The spark ignites the fuel-air mixture causing a mini explosion. The fuel burns immediately, giving off hot gas that for an instant raises the pressure dramatically and keeps the volume is unchanged. The piston is then pushed down releasing the energy from the fuel powering the crankshaft.
4) The outlet valve opens. It forces the exhaust gases out through the exhaust outlet.
34
Example of an adiabatic process within the internal combustion 4 stroke engine cycle?
Power stroke - ignite and goes bang
35
Why is a 4 stroke piston engine process considered to be a constant volume engine?
- Constant volume is injected into the system
(Otto cycle)
36
Why is the Brayton cycle in a gas turbine engine considered to be a constant pressure cycle?
- Suck, squeeze, bang, blow but simultaneously
- Constantly under pressure
37
How does a refrigerator/heat pump work?
- Absorbs heat energy from inside and transfers it outside
38
Define each part of the refrigeration process?
1) The compressor motor forces a coolant gas at high pressure through the condenser
2) As the coolant flows through thin radiator pipes in the condenser on the back of the fridge, heat is given
out and it condenses back into a liquid
3) The liquid coolant undergoes a sudden drop in pressure that
makes it expand
4) The coolant absorbs and removes heat from the food inside
5) Warmed gas is then returned to the compressor and re-compressed as the cycle
continues
39
Difference between a heat pump and a refrigerator?
Vapour cycle is reversed
40
Why are both refrigerators and heat pumps considered isothermal processes?
Constant temperature is maintained in both systems
41
If you raise the temperature of an ideal gas inside a cylinder with a fixed piston, what will happen to the pressure of the gas inside the cylinder?
- Increase pressure
- Isochoric process
42
Define latent heat?
Amount of heat required to cause a change in heat
43
What does latent heat of fusion describe?
Heat needed to change a solid into a liquid
Note - Fusion for white choc fusion
44
What does latent heat of vaporisation describe?
Heat needed to change a liquid into a gas
Note - Vapour for gas
45
If an ideal gas has its temperature locked and the container holding it is compressed - what happens to the pressure of the gas?
- Based on Boyle's law the pressure will increase
- Isothermal process
46
Define combustion?
Heat combustion is the heat released during the reaction
47
What happens during the process of combustion?
Hydrocarbon reacting with oxygen resulting in heat, carbon dioxide and water
48
Why are heat combustion valves important when comparing fuels?
The greater the heat of combustion of a substance the greater the amount
of energy produced when the fuel is burned
49
Define heat capacity?
Amount of heat required by a substance to rise a certain amount
50
Formula for heat capacity?
Q=CAT
Energy = heat capacity x change in temperature
51
Define the characteristics of a substance with a low heat capacity?
- Requires little to no heat to rise to a certain amount
- Metals like copper
52
Give an example of a substance with high heat capacity?
- Requires a lot of heat to rise a small amount
- Fibres like asbestos
53
Define heat specific?
- The amount of heat needed to rise the temperature of a substance
- Helps to determine if the substance is a conductor or insulator of heat
54
Formula for heat specific?
C = Q / m x AT
Specific heat = heat energy / mass x temperature change
OR
Q = MCAT
Heat energy = mass x specific heat x temperature change
55
Which temperature scales start at absolute zero?
- Kelvin
- Rankine
56
How do you convert degrees Celsius to Kelvin?
Kelvin = Celsius + 273
57
How do you convert from Kelvin to degrees Celsius?
Celsius = Kelvin - 273
58
How do you convert from Fahrenheit to degrees Rankine?
Rankine = Fahrenheit + 460
59
How do you convert from Rankine to Fahrenheit?
Fahrenheit = Rankine - 460
60
What is light?
All electromagnetic radiation
61
What is the speed of light in a vacuum?
3 x 10 to the power of 8 m s -1
62
What is a plane surface?
2D, perfectly flat surface that extends in all directions
63
What does 'normal' refer to when referring to a plane surface?
A line drawn perpendicular to the surface at the point of contact of the light ray
64
What is an incidental ray?
The incoming light ray moving towards the surface
65
What is a reflected ray?
The outgoing light ray reflected away from the surface
66
State the law of reflection?
The angle of incidence equals the angle of reflection
67
What is the main problem encountered when light reflects off a spherical reflector?
- Spherical aberration (results in poor focus of an image)
- Multiple focal points
68
How can we limit the effects of spherical aberration?
- Limiting the curvature
- Only using the central portion of the reflector
69
Main difference between spherical and parabolic mirrors?
- Spherical mirrors have uniform curvature and are part of a sphere
- Parabolic mirrors can be manufactured to give perfect focus
70
What is refraction?
Bending of light
71
What happens to light when it moves from a less dense medium to a more dense medium?
Slows down and bends towards the normal
72
What happens to light when it moves from a more dense medium to a less dense medium?
Bends away from the normal
73
What will light do when it passes through a convex lens?
Bend and converges together
74
What another term used to describe convex?
Converging lens
75
How are convex lenses used by aviation technicians?
Magnified glass used to make objects appear closer and clearer
76
What happens to light when it initially enters a fibre optic cable?
It is refracted
77
What is the importance of the acceptance angle in fibre optic operations?
Affects the propagation of the light rays once they enter the core
78
What is the importance of total internal reflection when dealing with fibre optic cables?
- Allows light / signal to be contained in the core
- Minimises loss of transmission signal
79
Name 3 applications for fibre optic cable in aircraft systems?
- Communication
- Automatic flight controls
- Navigation
80
Name 3 advantages for fibre optic cables in aircrafts?
- Light weight
- No electromagnetic interference
- Complete electrical isolation
81
Name 2 disadvantages for fibre optics in aircrafts?
- Radiation
- Glass cut offs
(Both above are safety concerns)
- Not as flexible
- Difficult to repair
82
Define the term wave?
Energy carriers, can move energy without moving the matter itself
83
Define the term damping?
Air resistance / friction
84
Define equilibrium position?
Natural resting position
85
Define periodic motion?
Motion that is regular and repetitive, such as a vibration
86
Define sinusoidal wave motion?
All naturally occurring periodic motion will produce a wave as the object oscillates around the equilibrium point.
87
How is the height of a waveform defined?
Measure from crest to crest
88
Define the term restoring force with reference to simple harmonic motion?
- Restoring force which always acts toward the equilibrium position, no matter where the object is
- If there were no restoring forces, damping would not occur and the vibration would continue on forever
89
The further an object moves from its equilibrium position, the less the restoring force becomes? True or false?
False - further the object is away from the equilibrium the greater the force becomes
90
Define resonance with reference to pendulums?
If the forces vibration is timed to match the natural
frequency, resonance will occur. This resonance will have the effect of increasing the amplitude of the vibration that occurs within the swinging pendulum.
91
Define fundamental frequency?
- Also known as first harmonic
- Natural frequency
92
Another name for fundamental frequency?
First harmonic
93
Define harmonics?
Multiples of a fundamental frequency
94
If a fundamental frequency is determines to be 60HZ, what is the forth harmonic?
240HZ
95
What is a mechanical wave?
Waves in which matter vibrates and the energy is transferred through a medium
96
How are mechanical waves different to electromagnetic waves?
Mechanical waves - require a medium
Electromagnetic waves - do not require a medium
97
2 types of mechanical waves?
- Transverse waves
- Longitudinal waves
98
What is the difference between transverse and longitudinal waves?
Transverse waves:
- Travel with the shape of a sin / cosine wave
- Move perpendicular
- Measured peak to peak
- Also known as sinusoidal waves
Longitudinal waves:
- Parallel to proportion
- Particles isolate back and forth
- Also known as compressional waves
99
Components of a transverse wave?
- crest / trough
- wavelength
- amplitude
- Equilibrium position
100
Components of a longitudinal wave?
- Areas of compression
- Refraction
101
What type of wave is a sound wave?
Longitudinal mechanical waves
102
Define frequency in reference to wave motion?
Amount of cycles per second
103
How do you measure the wavelength?
Crest to crest or trough to trough
104
How are period and frequency related?
Period is inversely proportional to frequency and vice versa
105
2 factors that determine the speed of a wave?
- Wavelength
- Frequency
106
A wave has a frequency of 50HZ and a wavelength of 2.4m. How fast is it travelling?
120m s -1
107
Define phase shift?
How much one sine wave is shifted relative to another
108
What is wave interference?
When two (or more) waves are travelling in the same medium and they meet, the displacements are added
to produce a resultant waveform
109
What is constructive interference and how might it occur?
- Peaks line up
- Summing affect
- Resultant amplitude will be greater than a single wave on its own
110
What is destructive interference and how might it occur?
- Two waveforms occurs at a time out of phase
- Cancel each other out when added together (same amplitude)
111
What does a standing wave look like?
It appears to stand still
112
Example for how destructive interference is applied in aviation?
Noise cancelling headphones
113
What causes a standing wave?
- When waves are reflected off of a surface
- Same wave length etc but are now out of phase
- Appear to be standing still
114
What are 2 parts of standing waves?
- Node
- Antinode
115
How do the 2 parts of a standing wave differ from each other?
116
What is a sound wave?
- Sound is a property of vibrating objects
- Needs matter to operate
117
How does a sound wave travel when given off from an object like a tuning fork?
- Mechanical disturbance causing it to vibrate
118
What 3 factors affect the speed of sound?
- Elasticity
- Density
- Temperature.
119
What would an increased in density do to the speed of sound in the air?
Reduction in speed
120
What would an increase in temperature do to the speed of sound in air?
Increase in speed
121
Which characteristic has the greatest effect on the speed of sound?
Elasticity
122
In terms of sound waves, what does sound intensity relate to?
Measure of amount of energy that can be transferred
123
What is the SI unit for acoustic power?
Watts per meters squared
124
Define the loudness of sound?
- Measurement of the ear’s response to sound
125
What is the sound intensity level and how is it measured?
Logarithmic ratio
126
3 factors that determine sound quality?
- Harmonic content
- Attack and decay
- Vibrato.
127
What is harmonic content?
Contain a fundamental frequency, but also multiples of it
128
What is attack and decay?
Attack: determines how long a sound takes to reach its full amplitude
Decay: how long the sound
lasts
129
What is vibrato?
Periodic changes in the pitch of a tone
130
How does the doppler effect occur?
- Change in apparent frequency by an observer is known as the Doppler Effect
EXAMPLE -
Train coming towards you = compressing the air = higher pitch
Train passes and continues away from you = air particles are spread further apart = lower pitch
131
How are the pitch of sound and frequency related?
Preserve high frequency has high pitch etc
132
Would a higher or lower frequency be heard is a source of sound was moving towards the receiver?
Higher as it approaches
133
Will the doppler effect be heard if there is no relative movement between the source and receiver of sound?
No
AV Fundies
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