(C1) Thermal Physics in Domestic and Industrial Applications Flashcards
1
Q
What are prefixes?
A
- Tera
- Giga
- Mega
- kilo
- centi
- milli
- micro
- nano
- pico
2
Q
Prefix Sizes
A
- Tera (x10¹²)
- Giga (x10⁹)
- Mega (x10⁶)
- kilo (x10³)
- centi (x10⁻²)
- milli (x10⁻³)
- micro (x10⁻⁶)
- nano (x10⁻⁹)
- pico (x10⁻¹²)
3
Q
What is the law of the conservation of energy?
A
Energy cannot be created or destroyed but can only change form
4
Q
What are the eight energy stores?
A
- Magnetic
- Thermal
- Chemical
- Kinetic
- Electrostatic
- Elastic Potential (EPE)
- Gravitational Potential (GPE)
- Nuclear
5
Q
What is EPE?
A
Elastic Potential Energy
6
Q
What is GPE?
A
Gravitational Potential Energy
7
Q
What is kinetic energy?
A
energy due to an object moving
8
Q
What is gravitational potential energy?
A
energy due to the position of an object in a gravitational field
9
Q
What is the equation for gravitational potential energy?
A
GPE = mass x gravitational field x height
10
Q
What is Earth’s gravitational field strength?
A
9.81
11
Q
What is thermal energy?
A
energy due to due to the temperature of an object
12
Q
What is elastic potential energy?
A
Energy due to energy stored when objects are stretched or compressed
13
Q
What is chemical energy
A
energy that is released by a chemical reactions (fuel and food)
14
Q
What is nuclear energy?
A
Energy caused by nuclear reactions (radioactivity, fission and fusion)
15
Q
What is electrostatic energy?
A
Energy from electric charges attracting or repelling
16
Q
What is magnetic energy?
A
energy from magnets attracting or repelling
17
Q
Ways of Transferring Energy
A
- Mechanically
- Electrically
- By Heating
- By Radiation
18
Q
What is the (Mechanically) way of transferring energy?
A
When a force moves through a distance
19
Q
What is the (Electrically) way of transferring energy?
A
When a charge moves through a potential difference
20
Q
What is the (By Heating) way of transferring energy?
A
Due to temperature difference
21
Q
What is the (By Radiation) way of transferring energy?
A
Due to light, sound, microwaves, etc …
22
Q
What is work done on a system?
A
Energy is added to the system, the work is negative
23
Q
What is work done by the system?
A
Energy is leaves the system, the work is positive
24
Q
What is work done (W) and what is it measured in?
A
When energy is transferred to move an object, measured in joules (J)
25
What is the equation of work done?
W = F × Δs
26
What is the F in the work done equation and what is it measured in?
Force, measured in Newtons (N)
27
What does the Δ in equations mean?
Δ means the change in something
28
What is the s in the work done equation and what is it measured in?
The distance the force has moved, measured in metres (m)
29
Equation for work done on or by a gas
W = p × ΔV
30
What is the symbol p and what is it measured in?
Pressure which is measured in pascals (Pa)
31
What happens when the temperature of a gas increases at a constant pressure?
The volume increases and work is done by the gas (negative)
32
What happens when the temperature of a gas decreases at a constant pressure?
The volume decreases and work is on the gas (positive)
33
How many kelvins is 0°C?
273K
34
What is power (P)?
The rate of doing work, so how fast energy is transferred
35
Equation of power
power = work done / time
36
What is power measured in?
Watts (W)
37
What is watt equivalent to?
One watt is equivalent to one joule per second
38
What is the symbol for time and what is it measured in?
t, measured in seconds (s)
39
What is 1 kWh in Joules?
3,600,000 J
40
How many units in 1 kWh?
One unit
41
What is efficiency?
The ratio of the useful energy output of a system to the total input energy
42
Equation for efficiency?
Efficiency = useful power output / total power output
43
What is heat transfer?
When objects touch, heat energy will be transferred from one to the other
44
What is thermal equilibrium?
When touching objects have the same temperature
45
What happens when two touching objects are in thermal equilibrium?
There will be no net transfer of heat energy between them
46
What thermal capacity and what is it measured in?
The energy required to raise the temperature of a substance by 1°C, measured in J K⁻¹
47
Equation for thermal capacity
thermal capacity = Q / ΔT
48
What is the Q in the thermal capacity and specific heat capacity equation?
What is it measured in?
(heat energy )
The amount of heat added or removed from the system, measured in joules
49
What is specific heat capacity (c) ?
The energy required to raise the temperature of 1kg of a substance by 1°C
50
Equation for specific heat capacity
Q=m x c x ΔT
51
What is specific latent heat (L) and what is it measured in?
The amount of heat added or removed to change a substance from one state to another
It is measured in J kg⁻¹
52
Equation for specific latent heat
Q = m x L
53
What is the specific latent heat of vaporisation of water?
How much energy is needed?
The energy need to change water to a vapour
2,260,000 J kg⁻¹
54
What is the latent heat of condensation?
When a vapor changes to a liquid
55
What is the specific latent heat of fusion of water?
When energy is removed and water turns into ice
336,000 J kg⁻¹
56
What is an ideal gas?
A gas that obeys the ideal gas law and its assumptions
57
Ideal gas assumptions
* Particles are in continuous random motion
* The volume of particles is very small compared to the volume of the gas
* Particles are a long way from each other and only interact when they collide
* Collisions are elastic (No kinetic energy is lost during collisions)
58
What is Brownian motion?
When fluids are made of particles which hit into things randomly
59
Equation for ideal gas
pV = NkT
60
What is N in the ideal gas equation?
The number of molecules in the gas
61
What is the k in the ideal gas equation?
Boltzmann constant, 1.38 × 10−⁻²³ J K⁻¹
62
What is the first law of thermodynamics?
heat energy supplied to a system either increases the temperature, changes the physical state or enables the system to do work
63
Equation of the first law of thermodynamics
Q = ΔU + W
64
What is the ΔU in the first law of thermodynamics equation?
The increase in internal energy
65
What happens if the work is done on the system for the first law of thermodynamics?
The first law of thermodynamics equation will become
Q = ΔU − W which will have a negative value
66
What does iso mean?
Fixed
67
What is isothermal?
Fixed temperature
68
What is isobaric?
Fixed pressure
69
What is isovolumetric /isochoric?
Fixed volume
70
When does a isothermal change occur?
When temperature is constant, ΔU = 0
71
What happens to the first law of thermodynamics during an isothermal change?
The first law of thermodynamics equation becomes Q = W
72
During a isothermal change if the gas expands what happens?
Work is done and heat must be supplied
73
During a isothermal change if the gas contracts what happens?
Heat is produced and must be allowed to leave the gas
74
What does gas need to be isothermally changed?
* It is in a good conducting, thin-walled container
* Temperature is constant
* The change occurs very slowly
75
What is a adiabatic change for ideal gas?
When no heat enter or leaves the gas, Q = 0
76
What happens to the first law of thermodynamics during an adiabatic change?
The first law of thermodynamics equation becomes ΔU = -W
77
During a adiabatic change if the gas expands what happens?
Work is done and the temperature of the gas falls
78
During a adiabatic change if the gas compressed what happens?
Work is done and the temperature of the gas rises
79
Is true adiabatic expansion possible?
No
80
What is a reversible adiabatic process called?
Isentropic
81
What happens in an engine?
1. A piston moves up in a cylinder to compress gas.
2. A spark heats the gas.
3. The heat causes the gas to expand, moving the piston down.
82
What is the second law of thermodynamics?
The transfer or conversion of heat energy is irreversible
83
Equations for the efficiency of a heat engine
1. efficiency = (Q₁ - Q₂) / Q₁
2. efficiency = W / Q₁
3. efficiency = 1 - (Q₂ / Q₁)
all of these are equal to each other, 1=2=3
84
What Q₁ in the heat engine equation?
Energy taken from a hot source
85
What Q₂ in the heat engine equation?
Energy given to a cold sink
86
Equations for the maximum theoretical efficiency of a heat engine
(Q₁ / Q₂) = (T₁ - T₂)
87
What T₁ in the maximum theoretical heat engine equation?
Temperature of the source, in kelvin
88
What T₂ in the maximum theoretical heat engine equation?
Temperature of the sink, in kelvin
89
What is coefficient of performance (COP)?
A ratio of the heat supplied to the high temperature reservoir to work done
90
COP equation
COP = T high / (T high - T low)
